| 1. |
- Baagherzadeh Hushmandi, Narmin, et al.
(author)
-
Numerical investigation of partial admission phenomena at midspan of an axial steam turbine
- 2007
-
In: Proceedings of the 7th European Conference on Turbomachinery: Fluid Dynamics and Thermodynamics, ETC 2007. - : European Conference on Turbomachinery (ETC).
-
Conference paper (peer-reviewed)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.
|
|
| 2. |
|
|
| 3. |
- Baagherzadeh Hushmandi, Narmin, et al.
(author)
-
Numerical Study of Unsteady Flow Phenomena in a Partial Admission Axial Steam Turbine
- 2008
-
In: Proceedings of ASME Turbo EXPO 2008. - New York : AMER SOC MECHANICAL ENGINEERS. - 9780791843154 ; , s. 713-722
-
Conference paper (peer-reviewed)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.
|
|
| 4. |
- Baagherzadeh Hushmandi, Narmin, et al.
(author)
-
Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines
- 2011
-
In: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 133:4, s. 041017-1-041017-12
-
Journal article (peer-reviewed)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.
|
|
| 5. |
- Dahlqvist, Johan, 1987-, et al.
(author)
-
TEST TURBINE INSTRUMENTATION FOR CAVITY PURGE INVESTIGATIONS
- 2014
-
In: The XXII Symposium on Measuring Techniques in Turbomachinery, Lyon, 4-5 September 2014.
-
Conference paper (other academic/artistic)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
|
|
| 6. |
- El-Gabry, Lamyaa, et al.
(author)
-
Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade
- 2015
-
In: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 137:8
-
Journal article (peer-reviewed)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.
|
|
| 7. |
- El-Gabry, Lamyaa, et al.
(author)
-
Measurements of Hub Flow Interaction on Film Cooled Nozzle Guide Vane in Transonic Annular Cascade
- 2012
-
In: Proceedings of the ASME Turbo Expo. - : ASME Press. - 9780791844748
-
Conference paper (peer-reviewed)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.
|
|
| 8. |
- Fridh, Jens, et al.
(author)
-
An experimental study on partial admission in a two-stage axial air test turbine with numerical comparisons
- 2004
-
In: Proceedings of the ASME Turbo Expo 2004. - Vienna : ASMEDC. ; , s. 1285-1297
-
Conference paper (peer-reviewed)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.
|
|
| 9. |
- Fridh, Jens, et al.
(author)
-
DYNAMIC FEATURES OF PARTIAL ADMISSION : OUTCOMES FROM ROTATING MEASUREMENTS
- 2007
-
In: Euroturbo 7. - Athens : Local Conference Organising Committee. ; , s. 451-462
-
Conference paper (peer-reviewed)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.
|
|
| 10. |
- Fridh, Jens
(author)
-
Experimental Investigation of Performance, Flow Interactions and Rotor Forcing in Axial Partial Admission Turbines
- 2012
-
Doctoral thesis (other academic/artistic)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.
|
|
