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1.	Alameldin, A., et al. (författare) CFD analysis of suction and pressure side film cooling influence on vane aero performance in a transonic annular cascade 2014 Ingår i: Proceedings of the ASME Turbo Expo. - 9780791845622 Konferensbidrag (refereegranskat)abstract Operating at temperatures well above their melting point, gas turbines' components are subject to terribly high thermal stresses. In order to keep them intact and performing, different cooling techniques are implemented. One of these methods is film cooling. Film cooling implementation in vane cascades has a potential loss expense. Proper assessment of its impact on the vane performance has to be conducted. The CFD approach of modeling each hole and cooling tube autonomously is very computationally expensive. In the current work an assessment of a new, more computationally efficient CFD approach for modelling film cooling was conducted on a vane cascade operating in the transonic regime (M =0.89). The film cooling holes were represented by orifice boundary condition at the vane surface, omitting the need to model internal coolant plenum and cooling tubes mesh, resulting in 180% reduction in grid size and attributed computational cost interpreted in 300% saving in computation time. Uncooled, and film cooled with different configurations and at different blowing ratios (BR) simulations were performed and compared to experimental measurements. A good agreement was obtained for the exit flow angles, vorticity and aerodynamic loss for all the cases (uncooled and cooled). Pitch-averaged exit flow angle outside endwalls regions remains unchanged for all cooling configurations and blowing ratios. The aerodynamic loss was found to be more sensitive to increasing the blowing ratio on the suction side than on the pressure side. The proposed approach of coolant injection modeling is shown to yield reliable results, within the uncertainty of the measurements in most cases. Along with lower computational cost compared to conventional film cooling modeling approach, the new approach is recommended for further analysis for aero and thermal vane cascade flows.
2.	Baagherzadeh Hushmandi, Narmin, et al. (författare) Numerical investigation of partial admission phenomena at midspan of an axial steam turbine 2007 Ingår i: Proceedings of the 7th European Conference on Turbomachinery: Fluid Dynamics and Thermodynamics, ETC 2007. - : European Conference on Turbomachinery (ETC). Konferensbidrag (refereegranskat)abstract This paper presents unsteady Navier-Stokes analysis to investigate partial admission phenomena in an axial two-stage steam turbine. The computations are performed in two-dimensional flow conditions at the midspan of the turbine with CFD software Fluent. Unlike some previous numerical work published in open literature, the partial admission in the present study is introduced into the model by blocking only one segmental arc (85.7°) of the guide vanes at the first stage. It is therefore necessary to model the whole annulus of the turbine in the numerical simulations. Results of the analysis show that the peak static pressure drop occurs downstream of the blockage at the entrance to the blocked region where emptying of the rotor channel occurs. The first stage rotor blades experience large static pressure changes on their surfaces and large tangential and axial forces. The magnitude of the tangential and axial forces is twice as large at the entrance to the cavity behind the blockage than at the exit of the blocked region. Entropy concentration downstream of the blockage is considerably high due to the nonuniformities in the flow field. The present results show good agreement between experiments and computations, in tendency of the circumferential static pressure at different axial cross sections. The difference between the numerical and experimental absolute values of the circumferential static pressure drop in the blocked region indicates that the three-dimensional effects are very important to the flow field behind the blockage.
3.	Baagherzadeh Hushmandi, Narmin, et al. (författare) Numerical Investigation of Partial Admission Phenomena at Midspan of an Axial SteamTurbine 2007 Ingår i: Proceedings of 7th European Conference on Turbomachinery,Fluid Dynamics and Thermodynamics. Konferensbidrag (refereegranskat)
4.	Baagherzadeh Hushmandi, Narmin, et al. (författare) Numerical Study of Unsteady Flow Phenomena in a Partial Admission Axial Steam Turbine 2008 Ingår i: Proceedings of ASME Turbo EXPO 2008. - New York : AMER SOC MECHANICAL ENGINEERS. - 9780791843154 ; , s. 713-722 Konferensbidrag (refereegranskat)abstract This paper presents a numerical investigation of unsteady flow phenomena in a two-stage partial admission axial steam turbine. Results from unsteady three-dimensional computations are analyzed and compared with the available experimental data. Partial admission in the present study is introduced into the model by blocking only one segmental arc of the inlet guide vanes. Blocking only one segment (which corresponds to the experimental setup) makes the model unsymmetrical; therefore it is necessary to model the whole annulus of the turbine. The first stage rotor blades experience large static pressure change on their surface while passing the blocked channel. The effect of blockage on the rotor blades' surface pressure can be seen few passages around the blocked channel. Strong changes of the blades' surface pressure impose large unsteady forces on the blades of first stage rotor row.The circumferential static pressure plots at different cross sections along the domain indicate how the non-uniformity propagates in the domain. A peak pressure drop is seen at the cross section downstream of the first stage stator row. At further downstream cross sections, the static pressure becomes more evenly distributed. Entropy generation is higher behind the blockage due to the strong mixing and other loss mechanisms involved with partial admission. Analysis of the entropy plots at different cross sections indicates that the peak entropy moves in a tangential direction while traveling to the downstream stages. Comparisons of the unsteady three-dimensional numerical results and the experimental measurement data show good agreement in tendency. However some differences are seen in the absolute values especially behind the blockage.
5.	Baagherzadeh Hushmandi, Narmin, et al. (författare) Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines 2011 Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 133:4, s. 041017-1-041017-12 Tidskriftsartikel (refereegranskat)abstract A numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Due to the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disk cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in the frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore, knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital to the design process of partial admission turbine blades. The pressure plots showed that the nonuniformity in the static pressure field decreases considerably downstream of the second stage's stator row, while the nonuniformity in the dynamic pressure field is still large. The numerical results between the first stage's stator and rotor rows showed that the leakage flow leaves the blade path down into the disk cavity in the admitted sector and re-enters downstream of the blocked channel. This process compensates for the sudden pressure drop downstream of the blockage but reduces the momentum of the main flow.
6.	Billson, Mattias, et al. (författare) Acoustic Cavity Resonances Driven by Shear Layer Instability 2024 Ingår i: 30th AIAA/CEAS Aeroacoustics Conference, 4 June - 7 June 2024, Rome, Italy. - : American Institute of Aeronautics and Astronautics (AIAA). Konferensbidrag (refereegranskat)abstract Flow over open cavities can give rise to resonances where the acoustic response in the cavity couples with the shear layer oscillations. In turbomachinery, there are several cavities in which such resonance may occur, for example the bleed cavities in the intercompressor duct. This work is a study of flow induced cavity resonance in a rectangular Helmholtz type cavity with variable depth and at a range of Mach numbers. The phenomenon is studied by means of experimental test data, computational fluid dynamics and analytical models. It is identified that the cavity during resonance can respond with both plane modes as well as higher order antisymmetric modes in the cavity. It is shown that the shear layer locks in to the cavity response with integer periods when the cavity responds with antisymmetric modes and half-integer periods when the cavity responds with symmetric modes. It is also observed that there are specific ranges in cavity resonance frequencies which strongly interact with the shear layer instability and that the resonance may switch between different resonance modes even at steady flow condition.
7.	Chandramouli, Sathyanarayanan, et al. (författare) Numerical characterization of entropy noise with a density based solver 2017 Ingår i: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017. - : European Turbomachinery Society. Konferensbidrag (refereegranskat)abstract In this work, dbnsTurbFoam, a new coupled density based solver, written in the framework of FOAM-EXTEND, is considered. The solver is first assessed on two canonical compressible flow scenarios, namely the Sod's shock tube and the ONERA S8 transonic channel. Results are compared with analytical formulations and experiments, respectively. 2-D Unsteady Reynolds Averaged Navier-Stokes simulations and 3-D Large Eddy Simulations of the flow within the passages of a geometrically simplified High Pressure Turbine Nozzle Guide Vane are then performed. Results are compared against experimental data in order to justify the geometrical simplifications made. Finally, the case of a sinusoidal temperature forcing at the inlet is considered in order to study the phenomenon of indirect combustion noise. Notably, the impact of the forcing on the vortex shedding dynamics and on the losses is discussed.
8.	Dahlqvist, Johan, et al. (författare) A Hands-On Student Lab for the Relation Between Unsteady Aerodynamics and Structural Dynamics 2016 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract A small plate is excited with sound from a portable speaker. Strain gauges and a fast data acquisition unit are used to measure the variations in surface strain on the plate. This is the setup of a new student laboratory to combine theory and practice within unsteady aerodynamics and structural dynamics.To clearly visualize and offer important hands-on lessons for graduate students in a master’s program in aeromechanics, a lab facility has been put together for the participants to study the interaction between unsteady aerodynamics and structural dynamics.The facility was run the first time with students during spring this year, with successful results both in terms of measurements and learning outcomes.
9.	Dahlqvist, Johan (författare) Cavity Purge Flows in High Pressure Turbines 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Turbomachinery forms the principal prime mover in the energy and aviation industries. Due to its size, improvements to this fleet of machines have the potential of significant impact on global emissions. Due to high gas temperatures in stationary gas turbines and jet engines, areas of flow mixing and cooling are identified to benefit from continued research. Here, sensitive areas are cooled through cold air injection, but with the cost of power to compress the coolant to appropriate pressure. Further, the injection itself reduces output due to mixing losses.A turbine testing facility is center to the study, allowing measurement of cooling impact on a rotating low degree of reaction high pressure axial turbine. General performance, flow details, and cooling performance is quantified by output torque, pneumatic probes, and gas concentration measurement respectively. The methodology of simultaneously investigating the beneficial cooling and the detrimental mixing is aimed at the cavity purge flow, used to purge the wheelspace upstream of the rotor from hot main flow gas.Results show the tradeoff between turbine efficiency and cooling performance, with an efficiency penalty of 1.2 %-points for each percentage point of massflow ratio of purge. The simultaneous cooling effectiveness increase is about 40 %-points, and local impact on flow parameters downstream of the rotor is of the order of 2° altered turning and a Mach number delta of 0.01. It has also been showed that flow bypassing the rotor blading may be beneficial for cooling downstream.The results may be used to design turbines with less cooling. Detrimental effects of the remaining cooling may be minimized with the flow field knowledge. Stage performance is then optimized aerodynamically, mixing losses are reduced, and the cycle output is maximized due to the reduced compression work. The combination may be used to provide a significant benefit to the turbomachinery industry and reduced associated emissions.
10.	Dahlqvist, Johan, et al. (författare) Experimental flow and performance investigations of cavity purge flows in a high pressure turbine stage 2015 Ingår i: 11th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2015. - : European Conference on Turbomachinery (ETC). Konferensbidrag (refereegranskat)abstract A high pressure turbine stage has been investigated from the aspect of flow and performance impact associated with cavity purge. Performance is referred to as the operating parameters of the turbine, mainly based on the continuous output torque monitoring. The flow parameters were studied through measurements featuring temperature and pressure throughout the flow path, as well as in the cavity. Purge and main flow velocities were quantified in the vane exit section, and degree of sealing based on purge-amount correlations and pressure readings. Results were related to turbine efficiency based on a simple correlation, and also entropy generation. Change of operating point was found to have a significant effect on degree of sealing, while the change of efficiency was found to be linear with respect to relative purge rate and independent of operating point.
11.	Dahlqvist, Johan, et al. (författare) Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds 2018 Ingår i: Journal of turbomachinery. - : ASME Press. - 0889-504X .- 1528-8900. ; 140:3 Tidskriftsartikel (refereegranskat)abstract The aspect of hub cavity purge has been investigated in a high-pressure axial lowreaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the cavities below the hub level from the hot main annulus flow. A fullscale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely, a high loading design case, and two high-speed points encompassing the peak efficiency. At each of these operating speeds, the amount of purge flow was varied from 0% to 2%. Observing the effect of the purge rate on measurement plane averaged parameters, a minor flow angle decrease and Mach number increase is seen for the low speed case, while maintaining near constant values for the higher operating speeds. The prominent effect due to purge is seen in the efficiency, showing a linear sensitivity to purge of 1.3%-points for every 1% of added purge flow for the investigated speeds. While spatial average values of flow angle and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible at higher span, with associated decreased turning. A radial efficiency distribution is utilized, showing negative impact through span heights from 15% to 70%. Pitchwise variation of investigated flow parameters is significantly influenced by purge flow, making this a parameter to include for instance when evaluating benefits of stator clocking positions.
12.	Dahlqvist, Johan, et al. (författare) EXPERIMENTAL INVESTIGATION OF TURBINE STAGE FLOW FIELD AND PERFORMANCE AT VARYING CAVITY PURGE RATES AND OPERATING SPEEDS 2016 Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO. - : AMER SOC MECHANICAL ENGINEERS. Konferensbidrag (refereegranskat)abstract The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the hot main annulus flow from cavities below the hub level. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely a high loading case, the peak efficiency, and a high speed case. At each of these operating speeds, the amount of purge flow was varied across a very wide range of ejection rates. Observing the effect of the purge rate on measurement plane averaged parameters, a minor outlet swirl decrease is seen with increasing purge flow for each of the operating speeds while the Mach number is constant. The prominent effect due to purge is seen in the efficiency, showing a similar linear sensitivity to purge for the investigated speeds. An attempt is made to predict the efficiency loss with control volume analysis and entropy production. While spatial average values of swirl and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible in the tip region, and an associated decreased turning. A radial efficiency distribution is utilized, showing increased impact with increasing rotor speed.
13.	Dahlqvist, Johan, et al. (författare) Purge Flow Impact on Turbine Stage and Seal Performance at Varying Cavity Purge Rates and Operating Speed Ingår i: International Journal of Turbomachinery, Propulsion and Power. - 2504-186X. Tidskriftsartikel (refereegranskat)abstract The impact of the wheelspace cavity purge flow on a high-pressure axial low-reaction turbine stage is investigated. Both the flow's sealing ability and the performance impact associated with its injection are studied. Two operating speeds are tested, namely a high loading case and the peak efficiency, with purge flow rates covering a wide range. As the purge flow is injected upstream of the rotor, the sealing effectiveness is quantified both radially and tangentially close to the rim seal, where the tangential variation is used to identify the seal mixing region. Having passed the rotor blading, the purge flow distribution in the main annulus is quantified, showing an influence of operating speed. The purge flow core is localized to the trace of the vane wake, however somewhat migrated while passing through the blading. The combination of measurements shows that the impact on flow parameters cannot be used to determine the spanwise transport of the purge flow; hence two techniques are necessary to both judge the spanwise transport and impact on flow. With known sealing effectiveness, industry correlations may be adapted to make use of the variation of necessary purge rate to obtain a certain degree of effectiveness at a given operating point, and thereby optimize the efficiency. Also the distribution of the coolant in the main flow path may be used to optimize film cooling in that area.
14.	Dahlqvist, Johan, et al. (författare) SEEDGAS INVESTIGATION OF TURBINE STAGE AND SEAL PERFORMANCE AT VARYING CAVITY PURGE RATES AND OPERATING SPEEDS 2017 Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO. - : AMER SOC MECHANICAL ENGINEERS. Konferensbidrag (refereegranskat)abstract The topic of hub cavity purge is investigated in a high-pressure axial low-reaction turbine stage. Both the sealing ability of the purge flow and the performance impact associated with its injection into the main flow are studied. Three operating speeds are investigated, namely a high loading case, the peak efficiency, and a high speed case, and purge flow rates across a wide range. The operating points coincide with investigations previously reported, where the flow field and stage efficiency was quantified using pneumatic probes. Comparative measurements are also performed, varying a leakage flow through the rotor below the hub platform. The purge flow is now seeded with CO2 in order to measure its distribution throughout the stage, as it is injected into the wheelspace upstream of the rotor, allowing for quantification of the sealing effectiveness. This is done at a number of defined locations along the stator-side wall in the wheel space, resolving the radial variation through the cavity. Important radial variations of effectiveness are observed, confirming that the flow is in the regime of merged boundary layers, due to the narrow cavity, as compared to typical gas turbine operation with separated. boundary layers. The trends are found to be related to operating speed and platform leakage. With known sealing effectiveness, industry correlations may be adapted to make use of the variation of necessary purge rate to obtain a certain degree of sealing at a given operating point, and thereby optimize the efficiency. In addition to quantification of potential hot-gas ingestion, the paper initiates an investigation of the transport of the purge flow in the main annulus, through sampling on the hub, as well as area traverse downstream of the rotor. The amount of sealing gas leads to opportunity to quantify the cooling performance of the purge flow in the main annulus. Both the cooling performance in the main annulus and cavity are shown to be significantly influenced by the rotor leakage, while its effect on efficiency is minor.
15.	Dahlqvist, Johan, 1987-, et al. (författare) TEST TURBINE INSTRUMENTATION FOR CAVITY PURGE INVESTIGATIONS 2014 Ingår i: The XXII Symposium on Measuring Techniques in Turbomachinery, Lyon, 4-5 September 2014. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract The upstream wheelspace of the KTH Test Turbine has been instrumented with the aim of investigating cavity flow phenomena, as well as cavity-main annulus interaction. Measurements include static pressure, unsteady pressure and temperature.The stage used is of high pressure steam turbine design. The trials include investigating the design point and also a high pressure, high speed operating point, assimilating gas turbine operation. At each point, varying amounts of purge flow are superposed and the influences on the measurements studied.Initial results show considerable dependence of both operating
16.	El-Gabry, Lamyaa, et al. (författare) Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade 2015 Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 137:8 Tidskriftsartikel (refereegranskat)abstract An experimental study has been performed in a transonic annular sector cascade of nozzle guide vanes (NGVs) to investigate the aerodynamic performance and the interaction between hub film cooling and mainstream flow. The focus of the study is on the endwalls, specifically the interaction between the hub film cooling and the mainstream. Carbon dioxide (CO2) has been supplied to the coolant holes to serve as tracer gas. Measurements of CO2 concentration downstream of the vane trailing edge (TE) can be used to visualize the mixing of the coolant flow with the mainstream. Flow field measurements are performed in the downstream plane with a five-hole probe to characterize the aerodynamics in the vane. Results are presented for the fully cooled and partially cooled vane (only hub cooling) configurations. Data presented at the downstream plane include concentration contour, axial vorticity, velocity vectors, and yaw and pitch angles. From these investigations, secondary flow structures such as the horseshoe vortex, passage vortex, can be identified and show the cooling flow significantly impacts the secondary flow and downstream flow field. The results suggest that there is a region on the pressure side (PS) of the vane TE where the coolant concentrations are very low suggesting that the cooling air introduced at the platform upstream of the leading edge (LE) does not reach the PS endwall, potentially creating a local hotspot.
17.	El-Gabry, Lamyaa, et al. (författare) Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade 2012 Ingår i: Proceedings of the ASME Turbo Expo. - : ASME Press. - 9780791844748 Konferensbidrag (refereegranskat)abstract An experimental study has been performed in a transonic annular sector cascade of nozzle guide vanes to investigate the aerodynamic performance and the interaction between hub film cooling and mainstream flow. The focus of the study is on the endwalls, specifically the interaction between the hub film cooling and the mainstream. Carbon dioxide (CO2) has been supplied to the coolant holes to serve as tracer gas. Measurements of CO2 concentration downstream of the vane trailing edge can be used to visualize the mixing of the coolant flow with the mainstream.Flow field measurements are performed in the downstream plane with a 5-hole probe to characterize the aerodynamics in the vane. Results are presented for the fully cooled and partially cooled vane (only hub cooling) configurations. Data presented at the downstream plane include concentration contour, axial vorticity, velocity vectors, and yaw and pitch angles. From these investigations, secondary flow structures such as the horseshoe vortex, passage vortex, can be identified and show the cooling flow significantly impacts the secondary flow and downstream flow field. The results suggest that there is a region on the pressure side of the vane trailing edge where the coolant concentrations are very low suggesting that the cooling air introduced at the platform upstream of the leading edge does not reach the pressure side endwall, potentially creating a local hotspot.
18.	Fridh, Jens, et al. (författare) An experimental study on partial admission in a two-stage axial air test turbine with numerical comparisons 2004 Ingår i: Proceedings of the ASME Turbo Expo 2004. - Vienna : ASMEDC. ; , s. 1285-1297 Konferensbidrag (refereegranskat)abstract This paper presents ongoing experimental aerodynamic and efficiency measurements on a cold flow two-stage axial air test turbine with low reaction steam turbine blades at different degrees of partial admission. The overall objectives of the work are to experimentally investigate and quantify the steady and unsteady aerodynamic losses induced by partial admission. The first results show that both the total-to-static turbine efficiency drops and that the efficiency peak appears at lower isentropic velocity ratios with lower degrees of admission. Detailed steady traverse measurements of the static wall pressures downstream of sector-ends show strong local variations. The pressure wake from the partial admission blockage moves almost axially through the turbine while the temperature wake is located in a tangential position that represents the position of a particle trace based on velocity triangles, in the direction of the rotor rotation. Comparisons with 2D compressible flow computations around the circumference demonstrate the importance of the radial flow component in these experiments.
19.	Fridh, Jens, et al. (författare) DYNAMIC FEATURES OF PARTIAL ADMISSION : OUTCOMES FROM ROTATING MEASUREMENTS 2007 Ingår i: Euroturbo 7. - Athens : Local Conference Organising Committee. ; , s. 451-462 Konferensbidrag (refereegranskat)abstract A system for rotating measurements has been designed and commissioned for a two-stage axial turbine of impulse design. Relative total pressure and strain gauge measurements in the rotating frame of reference have been performed during partial admission tests in this turbine. The overall project objectives are to determine unsteady aerodynamic losses related to admission sector-ends and rotor forcing functions. Some outcomes are presented and discussed herein. The unsteadiness in the measured relative total pressure is observed to be largest downstream of the suction side of the partial admission blockage where the high momentum fluid vividly interacts with the rotor. Strain gauge results show a high strain peak downstream of the suction side of the blockage. When reducing the shaft speed at constant pressure ratio, the dip in relative total pressure and the peak in tensile strain, that occur when a blade enters the blocked region, are shifted in the counter rotational direction. This is believed to reflect earlier emptying of the rotor blade channel. Furthermore, an increase of the flow capacity coefficient with a decrease of admission degree has been observed.
20.	Fridh, Jens (författare) Experimental Investigation of Performance, Flow Interactions and Rotor Forcing in Axial Partial Admission Turbines 2012 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The thesis comprises a collection of four papers with preceding summary and supplementary appendices. The core investigation solely is of experimental nature although reference and comparisons with numerical models will be addressed. The first admission stage in an industrial steam turbine is referred to as the control stage if partial admission is applied. In order to achieve high part load efficiency and a high control stage output it is routinely applied in industrial steam turbines used in combined heat and power plants which frequently operate at part load. The inlet flow is individually throttled into separate annular arcs leading to the first stator row. Furthermore, partial admission is sometimes used in small-scale turbine stages to avoid short vanes/blades in order to reduce the impact from the tip leakage and endwall losses. There are three main aspects regarding partial admission turbines that need to be addressed. Firstly, there are specific aerodynamic losses: pumping-, emptying- and filling losses attributed to the partial admission stage. Secondly, if it is a multistage turbine, the downstream stages experience non-periodic flow around the periphery and circumferential pressure gradients and flow angle variations that produce additional mixing losses. Thirdly, the aeromechanical condition is different compared to full admission turbines and the forcing on downstream components is also circumferentially non-periodic with transient load changes. Although general explanations for partial admission losses exist in open literature, details and loss mechanisms have not been addressed in the same extent as for other sources of losses in full admission turbines. Generally applicable loss correlations are still lacking. High cycle fatigue due to unforeseen excitation frequencies or due to under estimated force magnitudes, or a combination of both causes control stage breakdowns. The main objectives of this thesis are to experimentally explore and determine performance and losses for a wide range of partial admission configurations. And, to perform a forced response analysis from experimental data for the axial test turbine presented herein in order to establish the forced response environment and identify particularities important for the design of control stages. Performance measurements concerning the efficiency trends and principal circumferential and axial pressure distortions demonstrate the applicability of the partial admission setup employed in the test turbine. Findings reveal that the reaction degree around the circumference varies considerably and large flow angle deviations downstream of the first rotor are present, not only in conjunction to the sector ends but stretching far into the admission sector. Furthermore, it is found that the flow capacity coefficient increases with reduced admission degree and the filling process locally generates large rotor incidence variation associated with high loss. Moreover, the off design conditions and efficiency deficit of downstream stages are evaluated and shown to be important when considering the overall turbine efficiency. By going from one to two arcs at 52.4% admission nearly a 10% reduction in the second stage partial admission loss, at design operating point was deduced from measurements. Ensemble averaged results from rotating unsteady pressure measurements indicate roughly a doubling of the normalized relative dynamic pressure at rotor emptying compared to an undisturbed part of the admission jet for 76.2% admission. Forced response analysis reveals that a large number of low engine order force impulses are added or highly amplified due to partial admission because of the blockage, pumping, loading and unloading processes. For the test turbine investigated herein it is entirely a combination of number of rotor blades and low engine order excitations that cause forced response vibrations. One possible design approach in order to change the force spectrum is to alter the relationship between admitted and non-admitted arc lengths.
21.	Fridh, Jens, et al. (författare) Forced Response in axial turbines under the influence of partial admission 2012 Ingår i: ASME Turbo Expo 2012 - Turbine Technical Conference and Exposition, Copenhagen, June 11-15, 2012. - : ASME Press. - 9780791844731 ; , s. 1419-1429 Konferensbidrag (refereegranskat)abstract High cycle fatigue (HCF) due to unforeseen excitation frequencies or due to under predicted force magnitudes, or a combination of both causes control stage failures for steam turbine stakeholders. The objectives of this paper is to provide an extended design criteria toolbox and validation data for control stage design based on experimental data, with the aim to decrease HCF incidents for partial admission turbines. The upstream rotor in a two stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees stretching from 28.6% to 100% as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of first stator vanes by aerodynamically shaped filling blocks. Sweeps across a speed range from 50 to 105% of design speed are performed at constant turbine pressure ratio during simultaneous high speed acquisition. A forced response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low engine order forced responses because of the blockage, pumping, loading and unloading processes. Combinations of the number of rotor blades and low engine order excitations are the principal sources of forced response vibrations for the turbine studied herein. Altering the stator and/or rotor pitches will change the excitation pattern. A relation between the circumferential lengths of the admitted and non-admitted arcs that dictates the excitation forces is observed that may serve as a design parameter.
22.	Fridh, Jens, et al. (författare) Forced Response in Axial Turbines Under the Influence of Partial Admission 2013 Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 135:4, s. 041014- Tidskriftsartikel (refereegranskat)abstract High cycle fatigue (HCF) due to unforeseen excitation frequencies, underestimated force magnitudes, or a combination of both causes control-stage failures for steam turbine stakeholders. This paper provides an extended design criteria toolbox, as well as validation data, for control-stage design based on experimental data to reduce HCF incidents in partial-admission turbines. The upstream rotor in a two-stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees extend from 28.6% to 100%, as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of the first stator vanes with aerodynamically shaped filling blocks. Sweeps across a speed range of 50%-105% of design speed are performed at a constant turbine pressure ratio during simultaneous high-speed acquisition. A forced-response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low-engine-order forced responses because of the blockage, pumping, loading, and unloading processes. Combinations of the number of rotor blades and low-engine-order excitations are the principal sources of forced-response vibrations for the turbine studied here. Altering the stator and/or rotor pitches changes the excitation pattern. We observed that a relationship between the circumferential lengths of the admitted and nonadmitted arcs dictates the excitation forces and may serve as a design parameter.
23.	Fridh, Jens, et al. (författare) On the use of methane in rocket nozzle cooling channels : Bench scale trials 2018 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract A combination of conjugate heat transfer calculations and experiments in a dedicated test rig at Royal Institute of Technology (KTH), Sweden are performed in order to characterize methane’s impact on the nozzle cooling channels in terms of heat transfer, coking and pressure loss. The design procedure includes development of a numerical conjugate heat transfer model as well as inert trials, not only in order to validate model but more importantly to gain experience in order to reduce uncertainties in the final design. In the final design, the methane can be pre-heated to 655 K at pressure levels between 10 to 160 bars and enters the final heater that simulates the heat load from the flame-side with electric cartridges heating a well-insulated copper block. The heat flux is between 1 to 7 MW/m2 for cooling channel flows representative to a full-scale nozzle of an upper stage engine.
24.	Fridh, Jens, et al. (författare) REDUNDANT ROTATING MEASUREMENTS IN AN AXIAL COLD FLOW TEST TURBINE : Development and Procedure 2006 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract A rotating measurement system has been designed and commissioned for a cold flow test turbine and tested under the influence of partial admission. A shrouded turbine rotor of impulse design is equipped with miniature pressure transducers and strain gauges. This paper discusses the selected experimental design and procedure. Overall, the first test runs went well and necessary data were collected and could be evaluated accordingly. Encountered specific measurement technique problems are addressed where the importance of high redundancy is stressed. Results demonstrate one effect that imbedded sensor technology may encounter as regards of dynamic measurements and calibrations.
25.	Fridh, Jens, et al. (författare) Småskalig kraftvärme i framtiden 2002 Ingår i: Svenska Mekanisters Riksförening 2002:2, sid 14-17. Tidskriftsartikel (refereegranskat)
26.	Gao, Yang, 1988- (författare) Aerodynamic Design and Aeromechanical Analysis of Mixed and Radial Flow Turbines : A study on meanline method, stator tilting endwall design and forced response analysis 2021 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract In this energy transition era, turbocharging is still an important technology for the automotive industry to reduce fuel consumption and lower emissions in its vehicles. This importance can be seen from both conventional fossil-fuel powertrains, and emerging applications, such as increased utilization of biofuels along with hydrogen fuel cells. For automotive turbochargers, the turbine has mainly two alternative types, i.e., mixed flow turbines (MFTs) and radial flow turbines (RFTs). These devices are mature and commercially available yet still have significant potential for improvement towards ensuring higher performance, more robust operation, and lower cost. With this in mind the overall aim of this study is to improve the aerodynamic design and the aeromechanical analysis methods for MFTs and RFTs. Specifically, the investigation covers three research topics: meanline method, stator tilting endwall design, and forced response analysis. A meanline method tool is newly developed to predict the performance curves. For RFTs, the results present a generally good agreement between the predicted performance and experimental data. However, for MFTs, two limitations of loss models used in the meanline method have been identified: spanwise variation of incidence at the rotor inlet is neglected; and performance variations at different speeds cannot be captured by the investigated passage loss models. To overcome the first limitation, a multi-section incidence loss model is proposed. For the second limitation, more research work is suggested to investigate the effect of mixed-flow features at the MFT rotor inlet. As a contribution to investigate the mixed-flow feature at the MFT rotor inlet, different stator tilting endwall designs are numerically evaluated with computational fluid dynamics (CFD) tools. An MFT with well-documented experimental data is selected as the baseline and used to validate the CFD method. Performance improvement has been seen from those designs with a sharp turning on the shroud-side endwall just before the rotor leading edge. The optimal design in this study has a -45° tilting angle of the shroud-side stator endwall. It achieves approximate 1%-point higher efficiency than the baseline design over the 100% and 50% speed lines. Detailed aerodynamic analyses of the internal flow field contribute to the understanding of the performance change. After the aerodynamic design, aeromechanical analyses are necessary steps to achieve the mechanical robustness. In this part of the study the accuracy and the computational cost of different CFD methods are compared in the forced response analysis of an open-geometry RFT using three CFD methods – full annular, phase-lag, and non-linear harmonic (NLH)– for forcing predictions paired with time-domain and harmonic balance (HB) methods for the aero-damping predictions. It is found that for the stator-induced forcing, all three CFD methods predict the same pattern of forcing distribution. Taking the full annular method as the reference, the maximum blade displacement predicted by the other two methods has less than 15% deviation. However, for the volute-induced forcing, the NLH method is excluded due to increased computational cost. The phase-lag method predicts a distinct forcing distribution to the reference full annular method, leading to approximate 50% difference of the maximum blade displacement. When predicting the aero-damping, the reference time-domain and the HB methods predict similar log decrement values with less than 4.6% deviation. In terms of computational effort, the harmonic methods, namely NLH and HB, reduce the effort by a factor of 42 and 6 respectively for the forcing and aero-damping predictions compared with the reference method.
27.	Gao, Yang, 1988-, et al. (författare) Effect of Stator Tilting Endwall Designs onthe Performance of a Mixed Flow Turbineat Design and Off-design Operating Speeds Ingår i: Journal of engineering for gas turbines and power. - 0742-4795 .- 1528-8919. Tidskriftsartikel (refereegranskat)abstract A previous numerical study presented that the performance of a mixed flow turbine can be improved byimplementing stator endwall designs with a negative tilting angle on the shroud side. However, theprevious study was limited to the performance at the design speed and only a limited design matrix wasinvestigated due to the meshing strategy. The aim of this paper is to numerically evaluate the stator tiltingendwall designs at both the design and the off-design speeds and to exploit the design by extending theprevious design matrix. In this study, the stator endwall tilting angle on the shroud side varied between -35° and -65°. These tilted stator designs formed a sharp turning (‘kink’) on the shroud endwall at theupstream of the rotor leading edge. The performances of these designs were numerically investigated andwere compared with an experimentally validated baseline. The steady-state numerical results showed thatthe stator with a -45° shroud-endwall tilting angle was the optimal design to the investigated mixed flowturbine. Compared with the baseline, the stage efficiency of the tilted stator design increased within therange of 0.75%~1.5% points for 100% speed and 0.45%~0.9% for 50% speed. Meanwhile, no distinctefficiency change was seen at 75% speed. Unsteady simulations confirmed the efficiency improvement atthe 100% and 50% speeds. To explain the change of efficiency, the flow field was examined at fouroperating points. It was found the ‘kink’ structure induced a local flow separation which affected internalflow field of the rotor and thus reduced the entropy generation in the exhaust diffuser.
28.	Gao, Yang, et al. (författare) Numerical Investigation of the Performance Impact of Stator Tilting Endwall Designs on a Mixed Flow Turbine 2021 Ingår i: INTERNATIONAL JOURNAL OF TURBOMACHINERY PROPULSION AND POWER. - : MDPI AG. - 2504-186X. ; 6:2, s. 14- Tidskriftsartikel (refereegranskat)abstract This paper numerically investigates stator endwall designs for a mixed flow turbine. One key design parameter studied is the tilting angle of the stator endwall. By examining stator designs with different tilting angles, the aim of this paper is to improve the efficiency of the studied mixed flow turbine at low velocity ratio working conditions. The performance curve at the design speed was chosen for the comparison between the baseline design and the tilted endwall designs. First, the numerical predictions for the baseline design were validated with experimental data. Then, to understand the mechanism of the performance variation between the different designs, the internal flow field was analyzed in detail. It was found that the tilting stator endwall could form a geometric "kink" in the endwall profiles. On the shroud side, certain designs with such kink caused local flow separations upstream the rotor leading edge. This separation could have the effect of reducing the intensity of the tip leakage vortex and the exit kinetic energy losses at the rotor outlet and may also improve the performance of the exhaust diffuser. As a result, the peak of the efficiency curve shifted toward lower velocity ratio. If the turbine stage incorporated a downstream exhaust diffuser, the optimal design in this study showed a shift of the velocity ratio of the peak efficiency point from 0.62 to 0.60 compared with the baseline. The maximum efficiency improvement was 1.3% points, which occurred at low velocity ratio. Meanwhile, the peak efficiency was 0.2% points higher than the baseline. If the exhaust diffuser was removed, a similar shift of the efficiency curve was observed but less efficiency gain was achieved at the low velocity ratio condition. A preliminary unsteady simulation was also conducted for the optimal design in this study.
29.	Hammer, Steffen, et al. (författare) Experimental Investigation of Rossiter Modes for an Open Box Cavity With Adjustable Depth 2021 Ingår i: Proceedings of the ASME Turbo Expo. - : American Society of Mechanical Engineers (ASME). Konferensbidrag (refereegranskat)abstract Resonance in aerospace is a phenomenon that engineers have been trying to predict and avoid for a long time. Acoustic resonance is only a part in this field. When it was previously studied, it was mostly in connection with long slender gaps at the fuselage of aircrafts. Lately it has become a focus in the development of highly efficient aero engines. Bleed systems in the compressor part of engines are needed but not easy to place aerodynamically. Additionally, these bleed systems have complex geometries. These geometries coupled with the operational range of modern aircraft from low to high subsonic Mach numbers can create unwanted acoustic resonances.This paper is part of project study of these resonances. Here the bleed geometry is simplified to an open box cavity that is studied experimentally in order to measure its acoustic behavior in low to high subsonic flow. The experimental data is compared to theoretical prediction models to create a baseline for future studies. The results show a good agreement between Rossiter prediction and experiments for a shallow cavity of L/D=4. Deeper cavities with a length to depth ratio of one and 0.5 represent more organ pipe resonance phenomena. This is especially governed by the geometry of the cavity itself and the height of the test section. All cavities experience a shift in modes depending on the operating point. This mode shift pattern is similar for deeper cavities. However, the operating range can be divided into four sections in which a mode shift occurs for all cavities.
30.	Hammer, Steffen, et al. (författare) IDENTIFICATION OF CRITICAL ACOUSTIC MODES FOR AN OPEN BOX CAVITY WITH ADJUSTABLE DEPTH 2022 Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. - : International Council of the Aeronautical Sciences. ; , s. 2910-2922 Konferensbidrag (refereegranskat)abstract Aerospace engineers are facing increased challenges in designing the next generation of aero engines. Engines need to be lighter, compact, more powerful and consume less fuel. On the other hand the designs are supposed to be more reliable than before. Modern compressors in those engines are playing a big role in fulfilling parts of these requirements by increased aerodynamic efficiency. Additionally, increasing requirements on compactness forcing new designs that may alter the acoustic resonance picture significantly. All these design adjustments face additional risks of component damage or fatigue. Air bleed systems are necessary parts in the compressor section of an aero engine to allow a wider operational range. However, these bleed systems can additionally introduce acoustic resonance due to the nature of air flow over an opening. The bleed design needs to be adapted to avoid this kind of resonance as much as possible. This paper is a continuation of an experimental investigation of cavity resonance for an open box cavity. The operating range covers the typical flow speeds in aero engine low pressure compressors. The geometry of a compressor bleed system is simplified to allow the use of theoretical prediction models. The previous results of detected acoustic resonances are screened for critical modes in terms of amplitude. This screening identified vulnerable operating points at higher Mach numbers in the range of 0.65 to 0.8 for all cavity length to depth ratios between 4 and 0.5. The test data show that an interaction of Rossiter modes with other feedback mechanisms can significantly amplify the acoustic resonance.
31.	Heldens, Jules C., et al. (författare) On the characterization of methane in rocket nozzle cooling channels 2021 Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765 .- 1879-2030. ; 186, s. 337-346 Tidskriftsartikel (refereegranskat)abstract In recent years there has been a growing interest in methane as an alternative rocket fuel due to its favourable specific gravity, storage temperature and thermal stability, in addition to its ability to support In-Situ Resource Utilization. Due to these properties methane supports the ongoing design trend of strategic reduction in system complexity and increase of reusability. The current work presents a first step in addressing the lack of information in open literature on the characteristics of methane under conditions found in rocket nozzle cooling channels, i.e. elevated inflow temperature and a high single sided heat load. A new experimental facility has been established at KTH Royal Institute of Technology in cooperation with GKN Aerospace, and as part of ESA's Future Launcher Preparatory Programme. This facility is shown to enable direct measurement of the Heat Transfer Coefficient (HTC) of methane under a range of conditions, with a limited uncertainty and good repeatability. For inflow temperatures of around 400 K, mass flows up to 15 g/s and pressures up to 3 MPa, it has been observed that the effect of single sided heating results in a significant development of the flow field, which influences the heat transfer in second half of the test section. This development results in an increase of the HTC towards the end of the cooling channel. No significant effect of the pressure on the HTC has been observed under the current experimental conditions.
32.	Heldens, Jules C., et al. (författare) On the characterization of methane in rocket nozzle cooling channels 2020 Ingår i: Proceedings of the International Astronautical Congress, IAC. - : International Astronautical Federation, IAF. Konferensbidrag (refereegranskat)abstract In recent years there has been a growing interest in methane as an alternative rocket fuel due to its favourable specific gravity, storage temperature and thermal stability in addition to its ability to support In-Situ Resource Utilization. Due to these properties methane supports the ongoing design trend of strategic reduction in system complexity and increase of reusability. The current work presents a first step in addressing the lack of information in open literature on the characteristics of methane under conditions found in rocket nozzle cooling channels i.e. elevated inflow temperature and a high single sided heat load. A new experimental facility has been established at KTH - Royal Institute of Technology in cooperation with GKN Aerospace, and as part of ESA's Future Launcher Preparatory Programme. This facility is shown to enable direct measurement of the Heat Transfer Coefficient (HTC) of methane under a range of conditions, with a limited uncertainty and good repeatability. For inflow temperatures of around 400 K, mass flows up to 15 g/s and pressures up to 30 bar, it has been observed that the effect of single sided heating results in a significant development of the flow field, which influences the heat transfer in second half of the test section. This development results in an increase of the HTC towards the end of the cooling channel. No significant effect of the pressure on the HTC has been observed under the current experimental conditions.
33.	Horwood, Joshua T. M., et al. (författare) Flow Instabilities in Gas Turbine Chute Seals 2020 Ingår i: Journal of engineering for gas turbines and power. - : ASME. - 0742-4795 .- 1528-8919. ; 142:2 Tidskriftsartikel (refereegranskat)abstract The ingress of hot annulus gas into stator-rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurized purge required to protect highly stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations-which include a 360 deg domain-were undertaken using dlr trace's time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment. Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations. A comparison of computational domains ranging from 30 deg to 360 deg indicates that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60 deg sector and suggest that modeling an even number of blades in small sector simulations should be avoided.
34.	Horwood, Joshua T. M., et al. (författare) FLOW INSTABILITIES IN GAS TURBINE CHUTE SEALS 2019 Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO. - : ASME Press. Konferensbidrag (refereegranskat)abstract The ingress of hot annulus gas into stator-rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurised purge required to protect highly-stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations which include a 360 degrees domain - were undertaken using DLR TRACE's time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment. Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations. A comparison of computational domains ranging from 30 degrees to 360 degrees indicate that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60 degrees sector and suggest that modelling an even number of blades in small sector simulations should be avoided.
35.	Mamaev, Boris, et al. (författare) Aerodynamic investigation of turbine cooled vane block 2015 Ingår i: Thermal Engineering. - 0040-6015. ; 62:2, s. 97-102 Tidskriftsartikel (refereegranskat)abstract The vane block (VB) has been investigated and it gives several important results related to test methods and calculation procedures. The vane block is characterized by a developed film and convective cooling system. Blowing tests demonstrate that there is a weak correlation between cooling type and energy loss. Superposition of these effects is true for the central part over VB height without secondary flows. Coolant discharge increases profile loss and it rises if coolant flow rate is increased. Discharge onto profile convex side through the trailing edge slot influences the most considerably. The discharge through perforation decreases the vane flow capacity and insufficiently influences onto the flow outlet angle, but the trailing edge discharge increases this angle according to loss and mixture flow rate growth. The secondary flows reduce the effect of coolant discharge, which insufficiently changes losses distribution at turbine blades tips and even decreases the secondary losses. The flow outlet angle rises significantly and we are able to calculate it only if we correct the ordinary flow model. In the area of secondary flows, the outlet angle varies insufficiently under any type of cooling. This area should be investigated additionally.
36.	Mamaev, Boris, et al. (författare) The influence of a special fillet between the endwall and airfoil at the leading edge on the performance of the turbine nozzle diaphragm 2013 Ingår i: Thermal Engineering. - : Maik Nauka/Interperiodica. - 0040-6015 .- 1555-6301. ; 60:3, s. 217-222 Tidskriftsartikel (refereegranskat)abstract It is shown from the results of experimental investigations carried out on a nozzle diaphragm’s sector that an enlarged fillet at the vane leading edge does not have an essential effect on the flow and energy losses in the nozzle diaphragm
37.	Mironovs, A., et al. (författare) MODELING OF VARIABLE AERODYNAMIC FORCES IN TURBINE BASED ON EXPERIMENTAL DATA 2009 Ingår i: Proceedings of the 12th International Symposium on Unsteady Aerodynamics, Aeroacoustics & Aeroelasticity of Turbomachines ISUAAAT12 1-4 September 2009, Imperial College London, UK. - : Imperial College Press. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Effective methods of vibration diagnostics of a turbomachine’s flow duct are necessary for efficient condition based maintenance. Modern equipments provide extended opportunities for vibration measurements. However, there are few adequate models of high frequency vibration. A majority of the existing diagnostic techniques are limited within the low frequency range. This paper suggests the variable forces model intended for high frequency vibration diagnostics. For modeling of variable forces acting on the vane the test series are performed using a two-stage air test turbine. High frequency signals of total pressure and casing vibration are measured in order to investigate the airflow and vibration structure generated by the blades. Parameters of the blade wake are investigated and the wake’s dual nature is determined. Harmonic and random components of blade wakes are related to specific blade aerodynamic features as well as upstream airflow characteristics. Air duct failures are simulated with upstream static and rotating disturbances. The model of flow velocity oscillation, which acconts for both harmonic and random features of blade wakes is presented. Dynamic forces acting on a single vane are also modeled based on the model of blade wakes.
38.	Noor, Hina, et al. (författare) INVESTIGATION OF ONE-DIMENSIONAL TURBINE DESIGN PARAMETERS WITH RELATION TO COOLING PARAMETERS FOR A HIGH PRESSURE INDUSTRIAL GAS TURBINE STAGE 2011 Ingår i: 9TH EUROPEAN CONFERENCE ON TURBOMACHINERY. - : EUROPEAN TURBOMACHINERY SOC-EUROTURBO. ; , s. 557-568 Konferensbidrag (refereegranskat)abstract This parametric study describes the effects of design parameters on coolant consumption and performance loss of the first stage of a high pressure industrial gas turbine. The Lund University Axial Turbine (LUAX-T) tool is employed to develop a better coupling between design parameters, cooling air and aerodynamic losses. From the performed design study; a lower stage reaction degree decreases the rotor coolant requirement, mainly due to a resulting decrease in rotor inlet temperature. However, a low reaction degree increases the cooling losses for the vane, which is because of a direct proportion between the mixing losses and the local Mach number. Based on the performed calculations and loss predictions, a range of design parameters is recommended for first stage of a gas turbine, while considering the influence of this choice on the next stage. The loss calculated for the stator blade has been calibrated against existing experimental data.
39.	Noor, Hina, et al. (författare) Investigation of one-dimensional turbine design parameters with relation to cooling parameters for high pressure industrial gas turbine stage 2011 Ingår i: The 9th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics. Konferensbidrag (refereegranskat)
40.	Norton, S., et al. (författare) Modelling of turbine blade vibrations via computational intelligence methods 2017 Ingår i: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017. - : European Turbomachinery Society. Konferensbidrag (refereegranskat)abstract A method for modelling turbomachine blade vibration events is proposed, based on computational intelligence algorithms. The method utilises steady thermodynamic data and blade tip-timing data to identify high amplitude vibration events and to draw underlying relationships between steady-thermodynamic input channels and resultant blade motion characteristics. Several computational studies probe specific process aspects in order to improve model prediction accuracy and several methods of data-feature reduction are established to further enhance vibration predictions. Overall, the study shows promise of what prediction capabilities can be achieved with seemingly limited instrumentation. Drawbacks in matters of tip-timing interpretation, quality/quantity of data and process limitations are discussed. Consequential future objectives are outlined to envisage onward predictive accuracy.
41.	Petrov, Miroslav, 1971-, et al. (författare) High-Speed Steam Turbine Systems For Small-Scale Power Generation Applications 2012 Ingår i: Proceedings of the 20th International Conference on Nuclear Engineering collocated with the ASME 2012 Power Conference. - : ASME Press. - 9780791844960 ; , s. 651-657 Konferensbidrag (refereegranskat)abstract Energy utilization from low-grade fuels of either fossil or renewable origin, or from medium-temperature heat sources such as solar, industrial waste heat, or small nuclear reactors, for small-scale power generation via steam cycles, can be reasonably enhanced by a simple technology shift. This study evaluates the technical feasibility of a compact power generation package comprising a steam turbine directly coupled to a high-speed alternator delivering around 8 - 12 MW of electrical power. Commercial or research-phase high-speed electrical generators at MW-scale are reviewed, and a basic thermodynamic design and flow-path analysis of a steam turbine able to drive such a generator is attempted. High-speed direct drives are winning new grounds due to their abilities to be speed-controlled and to avoid the gearbox otherwise typical for small system drivetrains. These two features may offer a reasonable advantage to conventional drives in terms of higher reliability and better economy. High-speed alternators with related power electronics are nowadays becoming increasingly available for the MW-size market. A generic 8 to 12 MW synchronous alternator running respectively at 15,000 to 10,000 rpm, have been used as a reference for evaluating the fundamental design of a directly coupled steam turbine prime mover. The moderate steam parameter concept suits well for converting mid-temperature thermal energy into electrical power with the help of low-tech steam cycles, allowing for distributed electricity production at reasonable costs and efficiency. Steam superheat temperatures below 350 degrees C (660 degrees F) at pressures of maximum 20 bar would keep the steam volumetric flow sufficiently high in order to restrain the turbine losses typical for small-scale turbines, while helping also with simpler certification and safety procedures and using primarily established technology and standard components. The proposed steam turbines designs and their characteristics thereof have been evaluated by computer simulations using the in-house code ProSteam and its sub-procedures AXIAL and VaxCalc, by courtesy of Siemens Industrial Turbomachinery and its steam turbine division located in Finspong, Sweden. The first results from this study show that high-speed steam turbines of the proposed size and type are possible to design and manufacture based on conventional components, and can be expected to deliver a very satisfactory performance at variable power output.
42.	Petrov, Miroslav, 1971-, et al. (författare) High-speed Steam Turbine Systems for Distributed Generation Applications 2012 Ingår i: Proceedings of the ASME 2012 Power Conference. Power 2012. - : ASME Press. ; , s. 7- Konferensbidrag (refereegranskat)abstract The efficiency of utilization of low-grade solid fuels of either renewable or fossil origin such as biomass, municipal or agricultural wastes, peat, lignite, etc. for distributed generation applications and combined heat and power (CHP) production at small scales can be improved by a simple technology shift. This study evaluates the technical feasibility of a compact power generation package comprising a small steam turbine directly coupled to a high-speed alternator delivering around 2 MW of electricity. Existing high-speed electrical generators at MW-scale are presented and reviewed, and a basic thermodynamic design and flow-path analysis of a steam turbine able to drive such a generator is attempted. Most importantly, the speed-controlled turbogenerator arrangement promises improved electrical efficiency especially at part-load (in off-design mode), compared to the typically low off-design performance of small-scale steam cycles using state-of-art fixed speed turbines. High-speed alternators with related power electronics are nowadays becoming increasingly available for the MW-size market. One such product – a commercial 2 MW permanent-magnet alternator running at 22,500 rpm – has been used as a reference for evaluating the behavior of a speed-controlled steam turbine as a prime mover. The specific turbine losses due to its comparatively small size remain serious. However, a low steam parameter approach suits well for converting, for example, heat-only boilers into CHP units, adding value by local electricity production at affordable costs. Steam superheat temperatures of around or less than 350 C (660 F) would keep the steam volumetric flow sufficiently high in order to restrain the turbine losses and allow for a cost-effective electricity production for enhanced utilization of locally-available solid fuels via steam cycles. Such a steam turbine is possible to manufacture and would deliver a promising performance despite its small size. The possibility for the turbine to be speed-controlled and its characteristics thereof have been evaluated by computer simulations using the in-house code AXIAL by courtesy of the Swedish branch of Siemens Industrial Turbomachinery, steam turbine division. Simulation results show that a reasonable improvement in part-load performance can be achieved for the high-rpm turbine-generator drivetrain: up to 30% better in the load spectrum down to 50% of nominal output, if compared with a fixed-speed arrangement of similar size and parameters.
43.	Rijpkema, Jelmer Johannes, 1982, et al. (författare) Experimental investigation and modeling of a reciprocating piston expander for waste heat recovery from a truck engine 2021 Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 186 Tidskriftsartikel (refereegranskat)abstract Waste heat recovery using an (organic) Rankine cycle has the capacity to significantly increase the efficiency of heavy-duty engines and thereby reduce fuel consumption and CO2 emissions. This paper evaluates a reciprocating piston expander used in a Rankine cycle for truck waste heat recovery by quantifying its performance on the basis of experimental results and simulations. The experimental results were obtained using a setup consisting of a 12.8 L heavy-duty Diesel engine connected to a Rankine cycle with water and are used to calibrate a semi-empirical expander model. At an engine power between 75 and 151 kW, this system recovered between 0.1 and 3 kW, resulting in an expander filling factor between 0.5 and 2.5, and a shaft isentropic effectiveness between 0.05 and 0.5. The calibrated model indicated that the heat loss (16%), mechanical loss (6–25%), pressure drop (13–42%), and leakage (25–75%) all contributed significantly to the expander performance loss. A simulation study with acetone, cyclopentane, ethanol, methanol, and R1233zd(E), showed that a change of working fluid significantly impacts the expander performance, with the filling factor varying between 0.5 and 2.2 and the effectiveness between 0.01 and 0.5, depending on the working fluid, expander speed, and pressure ratio. The results of the optimization of the built-in volume ratio and inlet valve timing during a typical long haul driving cycle showed that acetone and R1233zd(E) provided the highest available power around 3 kW absolute, or 2.2% relative to the engine. The main contributions of this paper are the presentation of experimental results of an engine coupled to a Rankine cycle, and the quantification of performance losses and the effect of working fluid variation using an adapted semi-empirical expander model, which allows for a selection of the working fluid and geometrical modifications giving optimal performance during a long haul driving cycle.
44.	Roy, Arijit Sinha, et al. (författare) Flow instability effects related to purge through a gas turbine chute seal 2021 Ingår i: Journal of the Global Power and Propulsion Society. - : Global Power and Propulsion Society. - 2515-3080. ; 5, s. 111-125 Tidskriftsartikel (refereegranskat)abstract This paper investigates flow instabilities inside the cavity formed between the stator and rotor disks of a high-speed turbine rig. The cavity rim seal is of chute seal design. The influence of flow coefficient on the sealing effectiveness at constant purge flow rate through the wheel-space is determined. The effectiveness at different radial positions over a range of purge flow conditions and flow coefficients is also studied. Unsteady pressure measurements have identified the frequency of instabilities that form within the rim seal, phenomena which have been observed in other studies. Frequencies of these disturbances, and their correlation in the circumferential direction have determined the strength and speed of rotation of the instabilities within the cavity. Large scale unsteady rotational structures have been identified, which show similarity to previous studies. These disturbances have been found to be weakly dependent on the purge flow and flow coefficients, although an increased purge reduced both the intensity and speed of rotation of the instabilities. Additionally, certain uncorrelated disturbances have been found to be inconsistent (discontinuous) with pitchwise variation.
45.	Saha, Ranjan, 1984-, et al. (författare) Aerodynamic Implication of Endwall and Profile Film Cooling in a Transonic Annular Cascade 2013 Ingår i: 21st ISABE Conference. - Busan, Korea. Konferensbidrag (refereegranskat)abstract An experimental study is performed to observe the aerodynamic implications of endwall and profile film cooling on flow structures and aerodynamic losses. The investigated vane is a geometrically similar transonic nozzle guide vane with engine-representative cooling geometry. Furthermore, a new formulation of the cooling aerodynamic loss equation is presented and compared with the conventional methods. Results from a 5-hole pneumatic probe show that the film coolant significantly alters the secondary flow structure. The effect of different assumptions for the loss calculation is shown to significantly change the measured loss.
46.	Saha, Ranjan, et al. (författare) Aerodynamic implications of reduced vane count 2015 Ingår i: Proceedings of the ASME Turbo Expo. - : ASME Press. - 9780791856635 Konferensbidrag (refereegranskat)abstract Given the shortage of fossil fuels and the growing greenhouse effect, one strive in modern gas turbines is to make maximum usage of the burnt fuel. By reducing the number of vanes or blades and thereby increasing the loading per vane (or blade) it is possible to spend less cooling air, which will have a positive impact on the combined cycle efficiency. It also reduces the number of components and usage of metal and thereby also the cost of the engine. These savings should be achieved without any efficiency deficit in aerodynamic efficiency. Based on the fact, aerodynamic investigations were performed to see the aerodynamic implications of reduced vane number in a transonic annular sector cascade. The number of new nozzle guide vane was reduced with 24% compared to a previous design with higher vane count. The investigated vanes were two typical high pressure gas turbine vanes. Results regarding the loading indicated an expected increase with the reduced vane case. The minimum static pressure at the suction side is lower and at an earlier location for the reduced vane case and therefore, an extension of the trailing edge deceleration zone is observed for the reduced vane case. Results regarding losses indicate that even though the losses produced per vane significantly increases for the reduced vane case, a comparison of mass averaged losses between the reduced vane case and previous vane case show similar spanwise loss distributions. Assessing results leads to a conclusion that the reduction of the number of vanes in the first stage seems to be a useful method to save cooling flow as well as material costs without any significant deficit in overall efficiency.
47.	Saha, Ranjan, 1984-, et al. (författare) Aerodynamic Investigation of External Cooling and Applicability of Superposition 2015 Ingår i: 11th EUROPEAN CONFERENCE ON TURBOMACHINERY FLUID DYNAMICS AND THERMODYNAMICS. - : EUROPEAN TURBOMACHINERY SOC-EUROTURBO. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract An experimental investigation of the overall external cooling on a cooled nozzle guide vanehas been conducted in a transonic annular sector cascade. The investigated vane is a typicaltransonic high pressure gas turbine vane, geometrically similar to a real engine component.The investigations are performed for various coolant-to-mainstream mass-flux ratios. Resultsindicate that the aerodynamic loss is influenced substantially with the change of the coolingflow. Area-averaged exit flow angles in midspan region are unaffected at moderate filmcoolant flows, for all cooling configurations except for trailing edge cooling. The trailing edgecooling decreases the turning in all investigated cases. Results lead to a conclusion that bothtrailing edge and suction side cooling have significant influence on the aerodynamic losswhereas the shower head cooling is less sensitive to the loss. Investigations with individualcooling features essentially lead to the applicability of the superposition technique regardingthe aerodynamic loss for film cooled vanes, which is this paper’s contribution to the researchfield. Results show that the superposition technique can be used for the profile loss but not forthe secondary loss.
48.	Saha, Ranjan, 1984- (författare) Aerodynamic Investigation of Leading Edge Contouring and External Cooling on a Transonic Turbine Vane 2014 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Efficiency improvement in turbomachines is an important aspect in reducing the use of fossil-based fuel and thereby reducing carbon dioxide emissions in order to achieve a sustainable future. Gas turbines are mainly fossil-based turbomachines powering aviation and land-based power plants. In line with the present situation and the vision for the future, gas turbine engines will retain their central importance in coming decades. Though the world has made significant advancements in gas turbine technology development over past few decades, there are yet many design features remaining unexplored or worth further improvement. These features might have a great potential to increase efficiency. The high pressure turbine (HPT) stage is one of the most important elements of the engine where the increased efficiency has a significant influence on the overall efficiency as downstream losses are substantially affected by the prehistory. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage. Hence, this study has been incorporated into a research project that investigates leading edge contouring near endwall by fillet and external cooling on a nozzle guide vane with a common goal to contribute to the development of the HPT stage. In the search for HPT stage efficiency gains, leading edge contouring near the endwall is one of the methods found in the published literature that showed a potential to increase the efficiency by decreasing the amount of secondary losses. However, more attention is necessary regarding the realistic use of the leading edge fillet. On the other hand, external cooling has a significant influence on the HPT stage efficiency and more attention is needed regarding the aerodynamic implication of the external cooling. Therefore, the aerodynamic influence of a leading edge fillet and external cooling, here film cooling at profile and endwall as well as TE cooling, on losses and flow field have been investigated in the present work. The keystone of this research project has been an experimental investigation of a modern nozzle guide vane using a transonic annular sector cascade. Detailed investigations of the annular sector cascade have been presented using a geometric replica of a three dimensional gas turbine nozzle guide vane. Results from this investigation have led to a number of new important findings and also confirmed some conclusions established in previous investigations to enhance the understanding of complex turbine flows and associated losses. The experimental investigations of the leading edge contouring by fillet indicate a unique outcome which is that the leading edge fillet has no significant effect on the flow and secondary losses of the investigated nozzle guide vane. The reason why the leading edge fillet does not affect the losses is due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. The investigation of the external cooling indicates that a coolant discharge leads to an increase of profile losses compared to the uncooled case. Discharges on the profile suction side and through the trailing edge slot are most prone to the increase in profile losses. Results also reveal that individual film cooling rows have a weak mutual effect. A superposition principle of these influences is followed in the midspan region. An important finding is that the discharge through the trailing edge leads to an increase in the exit flow angle in line with an increase of losses and a mixture mass flow. Results also indicate that secondary losses can be reduced by the influence of the coolant discharge. In general, the exit flow angle increases considerably in the secondary flow zone compared to the midspan zone in all cases. Regarding the cooling influence, the distinct change in exit flow angle in the area of secondary flows is not noticeable at any cooling configuration compared to the uncooled case. This interesting zone requires an additional, accurate study. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the suction surfaces and does not reach the pressure side of the hub surface, leaving it less protected from the hot gas. This indicates a strong interaction of the secondary flow and cooling showing that the influence of the secondary flow cannot be easily influenced. The overall outcome enhances the understanding of complex turbine flows, loss behaviour of cooled blade, secondary flow and interaction of cooling and secondary flow and provides recommendations to the turbine designers regarding the leading edge contouring and external cooling. Additionally, this study has provided to a number of new significant results and a vast amount of data, especially on profile and secondary losses and exit flow angles, which are believed to be helpful for the gas turbine community and for the validation of analytical and numerical calculations.
49.	Saha, Ranjan, 1984-, et al. (författare) Experimental studies of leading edge contouring influence on secondary losses in transonic turbines 2012 Ingår i: ASME Turbo Expo 2012. - : ASME Press. - 9780791844748 ; , s. 1109-1119 Konferensbidrag (refereegranskat)abstract An experimental study of the hub leading edge contouring using fillets is performed in an annular sector cascade to observe the influence of secondary flows and aerodynamic losses. The investigated vane is a three dimensional gas turbine guide vane (geometrically similar) with a mid-span aspect ratio of 0.46. The measurements are carried out on the leading edge fillet and baseline cases using pneumatic probes. Significant precautions have been taken to increase the accuracy of the measurements. The investigations are performed for a wide range of operating exit Mach numbers from 0.5 to 0.9 at a design inlet flow angle of 90°. Data presented include the loading, fields of total pressures, exit flow angles, radial flow angles, as well as profile and secondary losses. The vane has a small profile loss of approximately 2.5 % and secondary loss of about 1.1%. Contour plots of vorticity distributions and velocity vectors indicate there is a small influence of the vortex-structure in endwall regions when the leading edge fillet is used. Compared to the baseline case the loss for the filleted case is lower up to 13 % of span and higher from 13% to 20 % of the span for a reference condition with Mach no. of 0.9. For the filleted case, there is a small increase of turning up to 15 % of the span and then a small decrease up to 35 % of the span. Hence, there are no significant influences on the losses and turning for the filleted case. Results lead to the conclusion that one cannot expect a noticeable effect of leading edge contouring on the aerodynamic efficiency for the investigated 1st stage vane of a modern gas turbine.
50.	Saha, Ranjan, et al. (författare) Influence of pre-history and leading edge contouring on aero-performance of a 3D nozzle guide vane 2013 Ingår i: Proceedings of the ASME Gas Turbine India Conference -2013- ; presented at ASME 2013 Gas Turbine India Conference, December 5-6, 2013, Bangalore, India. - : ASME Press. Konferensbidrag (refereegranskat)abstract Experiments are conducted to investigate the effect of the pre-history in the aerodynamic performance of a threedimensional nozzle guide vane with a hub leading edge contouring. The performance is determined with two pneumatic probes (5 hole and 3 hole) concentrating mainly on the endwall. The investigated vane is a geometrically similar gas turbine vane for the first stage with a reference exit Mach number of 0.9. Results are compared for the baseline and filleted cases for a wide range of operating exit Mach numbers from 0.5 to 0.9. The presented data includes loading distributions, loss distributions, fields of exit flow angles, velocity vector and vorticity contour, as well as, mass-averaged loss coefficients. The results show an insignificant influence of the leading edge fillet on the performance of the vane. However, the pre-history (inlet condition) affects significantly in the secondary loss. Additionally, an oil visualization technique yields information about the streamlines on the solid vane surface which allows identifying the locations of secondary flow vortices, stagnation line and saddle point.

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