| 1. |
- Allégret-Bourdon, Davy, et al.
(författare)
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Study of shock movement and unsteady pressure on 2D generic model
- 2006
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Ingår i: Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines. - Dordrecht : Kluwer Academic Publishers. - 1402042671 ; , s. 409-421
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Konferensbidrag (refereegranskat)abstract
- A flexible generic model has been developed at the Chair of Heat and Power Technology in order to perform fatter experiments in a more fundamental fashion. It is made of engineered flexible material and oscillate in a controlled way at non-uniform amplitude and variable frequencies. Time-resolved measurements of the unsteady surface pressures, the instantaneous model geometry as well as unsteady Schlieren visualizations are performed in order to study the shock wave motion and the aerodynamic load acting over this flexible generic bump. The model oscillates at reduced frequencies from 0.015 to 0.294 at transonic flow condition. The mode shapes of such a flexible bump strongly depends on the excitation frequency of the generic model. Schlieren pictures are obtained for an operating point characterized by an inlet Mach number of 0.63. Moreover, the presented results demonstrate that the phase of shock wave movement towards bump local motion shows a decreasing trend for the third bending mode shapes at reduced frequency higher than k=0.074. At the pressure taps located after the shock wave formation, the phase of pressure fluctuations towards bump local motion presents the same decreasing trend.
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| 2. |
- Chernysheva, Olga V., et al.
(författare)
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Influence of a vibration amplitude distribution on the aerodynamic stability of a low-pressure turbine sectored vane
- 2006
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Ingår i: Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines. - Dordrecht : Kluwer Academic Publishers. - 1402042671 ; , s. 17-29
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Konferensbidrag (refereegranskat)abstract
- A parametrical analysis summarizing the effect of the reduced frequency and sector mode shape is carried out for a low-pressure sectored vane cascade for different vibration amplitude distributions between the airfoils in sector as well as the numbers of the airfoils in sector. Critical reduced frequency maps are provided for torsion- and bending-dominated sector mode shapes. Despite the different absolute values of the average aerodynamic work between four-, five- and six-airfoil sectors a high risk for instability still exists in the neighborhood of realistic reduced frequencies of modern low-pressure turbine. Based on the cases studied it is observed that a sectored vane mode shape with the edge airfoils in the sector dominant provides the most unstable critical reduced frequency map.
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| 3. |
- Erlich, Catharina, et al.
(författare)
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Pyrolysis and gasification of pellets from sugar cane bagasse and wood
- 2006
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 85:10-11, s. 1535-1540
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Tidskriftsartikel (refereegranskat)abstract
- Wood pellets have become a popular form of biomass for power generation and residential heating due to easier handling both for transportation and for feeders in the treatment units, improved conversion and storage possibilities. The research on wood pellets as fuel has also been intensified during the past decade. However, other biomass sorts in pellet form, such as sugar cane bagasse, have not yet been extensively studied, especially not physical effects on the pellets during thermal treatment. Bagasse and wood pellets of different origin and sizes, shredded bagasse and wood chips have been studied in a thermogravimetric equipment to compare the effects of sort, origin, size and form of biomass during slow pyrolysis and steam gasification. Physical parameters such as decrease of volume and mass during treatment, as well as pyrolysis and gasification rates are of primary interest in the study. An important observation from the study is that for pellets the char density decreased during pyrolysis to a minimum around 450 degrees C, but thereafter increased with continued heating. The wood chips behaved differently with a continuous char density decrease during pyrolysis. Another conclusion from the work is that the size of the pellet has larger impact on the shrinkage behaviour throughout the conversion than the raw material, which the pellet is made of.
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| 4. |
- Fridh, Jens, et al.
(författare)
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REDUNDANT ROTATING MEASUREMENTS IN AN AXIAL COLD FLOW TEST TURBINE : Development and Procedure
- 2006
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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.
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| 5. |
- Green, Jeff
(författare)
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Controlling Forced Response of a High Pressure Turbine Blade
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vibration induced High Cycle Fatigue (HCF) is a major consideration in designing gas turbines. Indeed, the Gas Turbine manufacturer must demonstrate that the vibration level of the turbomachinery blading is acceptably low, usually by using an engine strain gauge test. If the test shows unacceptable vibration levels then a redesign is required which adds cost and time to the engine development programme. It is highly desirable, therefore to develop a capability which can predict the vibration level of the blade to ensure that it will be robust. The High-Pressure Turbine is of particular interest because of the harshness of the environment in which it operates (high mechanical speed and high air temperatures and pressures) so friction dampers are routinely introduced to control the vibration level. The friction dampers can introduce a degree of non-linearity into the structure which affects not only the vibration amplitude, but also the resonant frequency. The resonant frequency, amplitude, damper behaviour and aerodynamic forcing are all inter-related such that they must be considered as a single system. This thesis describes the development of two new approaches to predict the vibration behaviour of a High-Pressure Turbine blade including the effect of friction dampers. The first utilises existing prediction tools for modelling of the fluid, the structure and the friction behaviour, but uses a novel method for coupling the various aspects together. This approach is based on modelling an ‘engine acceleration’ across a wide speed range and prescribing the variation of all the relevant parameters with shaft speed. For example, both the excitation force on the blade and the centrifugal load of the damper vary strongly with rotor speed so these effects must be included in the analysis. The second approach extends the first approach by using a new iterative ‘resonance tracking’ methodology in which the aerodynamic boundary conditions are adjusted based on the shaft speed at resonance until convergence is reached. Both methodologies calculate the resonant frequency, amplitude and operating condition of each mode of interest as an output of the analysis. The engine acceleration methodology has been investigated in detail and has been validated against several High-Pressure Turbine cases. It has been found to be reliable: the amplitude predictions were in broad agreement with the available engine strain gauge results and the frequency shift introduced by the damper was in very good agreement. The methodology captures some important features of the physical system such as (a) the amplitude dependence of the damper, (b) the sudden drop in frequency when approaching the second flap resonance because the damper starts to slide, and (c) the effect of the damper on the ratio between stress and tip displacement. One rather surprising result was that in certain cases, where the forcing level was low, the damper increased the blade response because it moved the resonance to a higher shaft speed where the forcing level was larger. The main advantage of the method is its speed, which allows optimisation of key parameters within design timescales. The resonance tracking methodology has been compared directly with the engine acceleration approach on one of the test cases and it produced very similar results. Convergence was achieved quickly, in two or three iterations for the chosen test case, mainly because the blade surface pressure distribution was consistent across a broad speed range. The method showed that the first torsion resonance was more sensitive to aerodynamic conditions than the second flap mode, and may offer an explanation for the scatter seen in engine test results. The approach offers the advantage that it is more generally applicable, because it can deal with cases where the pressure distribution is sensitive to shaft speed, but it can only converge to a single mode and requires significantly more computational effort. The methodologies have been used to explore vibration reduction strategies such as wake shaping, damper optimisation and defining acceptance limits for the orientation of the single crystal material used in turbine manufacture. Overall these provided almost an order of magnitude reduction in blade response.
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| 6. |
- Green, Jeff, et al.
(författare)
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Scaling of Turbine Blade Unsteady Pressures for Rapid Forced Response Assessmen
- 2006
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Ingår i: Proceedings of the ASME Turbo Expo 2006, Vol 5, Pts A and B. ; , s. 1081-1089
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Konferensbidrag (refereegranskat)abstract
- High Cycle Fatigue caused by high vibration levels continues to be a major concern in gas turbine design. The use of Computational Fluid Dynamics methods is becoming more commonplace for calculating the vibration amplitude of turbomachinery blades during the design process. A typical calculation approach would be to calculate the unsteady aerodynamic loads at the resonance condition for each vibration mode of interest. In this paper it is proposed that, for a choked high pressure (HP) turbine, an unsteady flow prediction can be scaled across a wide engine operating range using a few simple parameters.There is a fixed relationship between the turbine inlet pressure and the HP shaft speed (when expressed nondimensionally) which can be used to scale the flow conditions. The effects of altitude, variation in the ratio of shaft speeds, compressor bleed flows and schedule of the variable vanes are secondary, having only a small influence on the behaviour.This paper demonstrates that the steady flow distribution around both stator and rotor is virtually constant across the speed range of the engine and the rotor unsteady surface pressure distribution shows only small differences. Further, the parameter which is of prime interest for vibration assessment, the modal force, can be scaled very well using turbine inlet pressure. For modes of vibration with high amplitudes the errors introduced by scaling are of the order of 6% which is considered acceptable for design predictions.
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| 7. |
- Jayasuriya, Jeevan, et al.
(författare)
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Experimental investigations of catalytic combustion for high-pressure gas turbine applications
- 2006
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Ingår i: Proceedings of the ASME Turbo Expo 2006, Vol 1. - 0791842363 ; , s. 763-771
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Konferensbidrag (refereegranskat)abstract
- Catalytic combustion has proven to be a suitable alternative to conventional flame combustion in gas turbines for achieving Ultra-Low Emission levels (ULE). In the process of catalytic combustion, it is possible to achieve a stable combustion of lean fuel/air mixtures which results in reduced combustion temperature in the combustor. The ultimate result is that almost no thermal-NOx is formed and the emissions of carbon monoxide and hydrocarbon emissions are reduced to single-digit limits. Successful development of catalytic combustion technology would lead to reducing pollutant emissions in gas turbines to ultra-low levels at lower operating costs. Since the catalytic combustion prevents the pollutant formations in the combustion there is no need for costly emission cleaning systems.
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| 8. |
- Jayasuriya, Jeevan, et al.
(författare)
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Gasified biomass fuelled gas turbine : Combustion stability and selective catalytic oxidation of fuel-bound nitrogen
- 2006
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Ingår i: Proceedings of the ASME Turbo Expo 2006, Vol 1. - 0791842363 ; , s. 773-780
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Konferensbidrag (refereegranskat)abstract
- Low heating value of gasified biomass and its fuel bound nitrogen containing compounds challenge the efforts on utilizing gasified biomass on gas turbine combustor. Low heating value of the gas brings along combustion stability issues and pollutant emission concerns. The fuel bound nitrogen present in gasified biomass could completely be converted to NOx during the combustion process. Catalytic combustion technology, showing promising developments on ultra low emission gas turbine combustion of natural gas could also be the key to successful utilization of biomass in gas turbine combustor. Catalysts could stabilize the combustion process of low heating value gas while the proper design of the catalytic configuration could selectively convert the fuel bound nitrogen into molecular nitrogen. This paper presents preliminary results of the experimental investigations on combustion stability and nitrogen selectivity in selective catalytic oxidation of ammonia in catalytic combustion followed by a brief description of the design of catalytic combustion test facility. The fuel-NOx reduction strategy considered in this study was to preprocess fuel in the catalytic system to remove fuel bound nitrogen before real combustion reactions occurs. The catalytic combustion system studied here contained two stage reactor in one unit containing fuel preprocessor (SCO catalyst) and combustion catalysts. Experiments were performed under lean combustion conditions (lambda value from 6 up to 22) using a simulated mixture of gasified biomass. The Selective Catalytic Oxidation approach was considered to reduce the conversion of NH3 into N-2. Results showed very good combustion stability, higher combustion efficiency and good ignition performances under the experimental conditions. However, the selective oxidation of fuel bound nitrogen into N-2 was only in the range of 20% to 30% under the above conditions.
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| 9. |
- Jöcker, Markus, et al.
(författare)
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Comparison of models to predict low engine order excitation in a high pressure turbine stage
- 2006
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Ingår i: Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines. - Dordrecht : Kluwer Academic Publishers. - 1402042671 ; , s. 145-159
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Konferensbidrag (refereegranskat)abstract
- The paper compares three numerical strategies to predict the aerodynamic rotor excitation sources of "Low Engine Order" (LEO) in a high-pressure turbine stage. Main focus is laid on methods to compute the stator exit flow. The aim is to evaluate computationally cheap approaches to avoid modeling the whole circumference of the stator. A single passage viscous strategy, a single passage inviscid linear blade movement strategy, and a viscous multi-passage sector strategy are compared and evaluated. The assessment of the prediction quality is made by comparison of the computed stator exit flow to experimental data. The main result is that only the global behavior of the stator exit flow is estimated right, both the level and amplitude of Mach number and pressure are computed with poor agreement to experiments. Future evaluations of the resulting rotor excitation pressure are needed to estimate the level of necessary agreement to give acceptable predictions of the low engine order forced response.
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| 10. |
- Martin, Andrew, et al.
(författare)
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SUSPOWER and ENGAS : Two major European research infrastructures in the gas turbine and energy conversion fields
- 2006
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Ingår i: Proceedings of the ASME Turbo Expo 2006, Vol 1. - 0791842363 ; , s. 1015-1022
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Konferensbidrag (refereegranskat)abstract
- Since the mid-1990's the European Commission (EC) has provided funding for transnational access schemes that open up existing major research facilities to outside users. In the current 6th Framework Program, two out of 14 funded projects - SUSPOWER and ENGAS - are of prime interest to the gas turbine community. SUSPOWER (KTH, Stockhom, Sweden) encompasses unique large-scale experimental facilities within the area of sustainable thermal power generation. Topics of key interest include high-temperature air combustion, catalytic combustion, gasification, aeroelasticity of turbine/compressor blades, film cooling aerodynamics, and stator/rotor interactions. ENGAS (NTNU, Trondheim, Norway) includes a complex array of specialized laboratories in the topic of environmental gas management. Relevant research topics include combustion of hydrogen and hythane, biomass gasification, CO2 absorption and sequestration, membranes for hydrogen and CO2 separation, gas storage in rock caverns, and hydrogen production and storage. This paper presents information on these projects along with a brief overview of previous EC transnational access activities as related to gas turbine research and development.
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