Department of Engineering - Annual Report 1997/98

Turbomachinery

References

Turbomachinery

The Whittle lab continues to work at the forefront of turbomachinery aerodynamics and in close collaboration with industry. The laboratory has excellent experimental and computational facilities and most research projects use a combination of these to solve the problems encountered. This close integration of experiment and computation is felt to be especially valuable for the training of research students. The laboratory works extremely closely with industry, especially with Rolls Royce plc, and the results of the research are often applied to real machines in a remarkably short timescale.

The model steam turbine is being used to examine the implications of unsteady flow in multistage turbines under the joint sponsorship of Siemens and EPSRC. A set of new low reaction blading has been designed and is currently being manufactured. This will be compared with the high-load 50% reaction design previously tested and with a future design intended to exploit the effects of unsteady flow(C23). The model intermediate pressure turbine has been used to examine the effects of the inlet flow on turbine performance. It has been found that a high total pressure near the casing significantly improves turbine efficiency whilst a low total pressure causes a dramatic reduction. A new set of stator blades is being designed for this turbine.

The new algorithm developed last year has been incorporated into several CFD codes. The algorithm is ideal for unsteady calculations giving about 40% increase in speed coupled with improved accuracy. However, for steady calculations the algorithm sometimes gives problems with the boundary conditions and these are proving very difficult to overcome. A new `dual time stepping' approach to unsteady calculations is being developed and shows promise of greatly reduced computer times for fine-grid calculations.

CFD codes have been extensively used for the design of industrial turbines and compressors. An extensive investigation of the design of transonic fans for large civil aero engines has led to a new design which shows promise of significant improvements in performance. A study of the implications of aerodynamic design on the noise produced by such fans is in progress as part of a European collaborative programme (RESOUND). A new design with significantly lower tip speed has been produced and will be tested by Rolls Royce as part of this programme. A second new low-noise design is in progress and this will also be tested.

Research aimed at improving the understanding of the flow through the radial turbines of turbochargers continues. Detailed experimental and computational examinations have been made of the tip clearance flows as well as studies of the effects of changing tip geometry on the overall performance. The results have been used to explain the existing industrial correlations and to make suggestions regarding future designs(C2,C3).

The combined theoretical-experimental study of the aerodynamic penalties of film cooling continues. Much of the recent work has been aimed at using computational methods to aid the design process. This work builds directly on the results obtained using experimental techniques that were developed for the determination of film-cooling effectiveness. A part of this work is concerned with the effects of cooling the hub and casing(C11). An investigation of the effect of cooling geometry in industrial gas turbines is also underway.

Research is being conducted into the effects of incident wakes on the transition to turbulent flow of laminar boundary layers and separation bubbles. This is important in the Low-Pressure turbines of aircraft engines. The work involves using linear cascades that are fitted with a moving bar system that simulates the presence of the upstream blade row(C20). Complementary work is now being conducted in the transonic cascade facility. Recent work in full-scale turbines at BMW Rolls-Royce has led to a 20 percent reduction in the number of airfoils in the Low Pressure Turbine of the BR715 engine for the Boeing 717(C12). Current work is aimed at more radical changes. While much of this work has been experimental, CFD is being used to aid the interpretation of the results. Design tools are also under development. More fundamental research is being carried out in conjunction with the University of Oxford(C25,C26) with the aim of providing improved models of the transition process.

The transonic probe calibration facility continues to be used for the investigation and calibration of miniature probes that are often used in high-speed research rigs. Developments in probe miniaturisation and response have been evaluated in conjunction with several sponsors. A novel data reduction algorithm has recently been developed which will allow further miniaturisation as well as reductions in run-time cost of experiments(C2).

Methods for simulating the performance of turbomachinery bladerows operating in circumferentially non-uniform flows have been successfully developed. These methods greatly ease the problems of ensuring aerodynamic compatibility between gas turbines and their installations(C16,C17,C22).

Two quite different aspects of two-phase flows in turbomachinery have provided recent research interest. In wet-steam turbines, the difficult problem of interpreting pitot probe pressure measurements when the flow contains vast numbers of submicron water droplets has been addressed via a theoretical study. This has resulted in the development of a simple practical method of correcting the raw experimental data. Calculations show that it is essential to apply these corrections if accurate loss estimates are to be obtained from experimental measurements in steam turbines(C24).

The use of "dirty" fuels in gas turbines causes serious problems of deposition and erosion. A project, supported by PowerGen, has been investigating the processes by which small particles (such as coal ash) are transported through turbulent boundary layers to solid surfaces. This has resulted in a new theory of particle deposition from turbulent flows. The theory has now been incorporated into a numerical calculation scheme for predicting particle transport and deposition in two-dimensional cascade flows using an Eulerian (rather than the more usual Lagrangian) formulation. The scheme is stable for a very wide range of Stokes numbers and is effective in capturing concentration discontinuities at the edge of particle-free `shadow zones'(C21). Cooperation with the Gas Turbine Laboratory at Massachusetts Institute of Technology led to three papers, two on centrifugal compressors(C6,C9), and one on tip clearance flow in axial compressors(C18).

The focus in turbomachinery CFD is now firmly on unsteady flow, design optimisation and turbulence/transition modelling. The interest in unsteady flow is in understanding the flow physics associated with blade row interactions and also attempting to predict the blade row acoustics (transonic fan noise is being studied under the RESOUND programme). The emphasis on unsteady flow is causing renewed interest in algorithm developments to force the very biggest problems onto current computer resources. Two VKI lectures were delivered in this area(C4,C5).

Design optimisation research attempts to automate the "traditional" uses of CFD in design(C7) and to explore more systematically blade row parameterisations. A PhD has just started, funded by Rolls-Royce plc, looking at the optimisation of an axial compressor stage.

Dr I.J. Day has been awarded the 1997 ASME International Gas Turbine Award for his paper `A Study of Spike and Modal Stall Phenomena in a Low-Speed Axial Compressor'(C1). Professor J.D. Denton was awarded the International Gas Turbine Institute's "Aircraft Engine Technology Award" for 1998. Dr H.P. Hodson was awarded the ASME Melville Medal for 1998 for the best paper in Mechanical Engineering. (Halstead, D.E., Wisler, D.C., Okiishi, T.H., Walker, G.J., Hodson, H.P., Shin, H-W. Boundary layer development in axial compressors and turbines. Parts 1 to 4. Transactions of the ASME Journal of Turbomachinery, 119, 114-127, 128-139, 225237, 426-444 (1997). Annual Report 1996/97 B10-B13. )

C1. Camp, T.R., Day, I.J. A study of spike and modal stall phenomena in a low-speed axial compressor. Transactions of the ASME, Journal of Turbomachinery, 120, (3), 393-401 (July 1998).

C2. Dambach, R., Hodson, H.P. Single-sensor fast response pressure probes - the "least-squares" method of data reduction. 14th Symposium on Measuring Techniques in Transonic and Supersonic Flow in Cascades and Turbomachines, Limerick, Ireland (September 1998).

C3. Dambach, R., Hodson, H.P., Huntsman, I. An experimental study of tip clearance flow in a radial inflow turbine. Proceedings, ASME International Gas Turbine and Aeroengine Congress and Exposition, Stockholm, Sweden, ASME Paper 98-GT-467 (June 1998).

C4. Dawes, W.N. Simulation of unsteady blade row interaction with CFD: applications. In: Blade Row Interference Effects in Axial Turbomachinery Stages. VKI Lecture Series 1998-02 (Von Karman Institute for Fluid Mechanics, 1998).

C5. Dawes, W.N. Simulation of unsteady blade row interaction with CFD: background. In: Blade Row Interference Effects in Axial Turbomachinery Stages. VKI Lecture Series 1998-02 (Von Karman Institute for Fluid Mechanics, 1998).

C6. Deniz, S., Greitzer, E.M., Cumpsty, N.A. Effects of inlet flow field conditions of the performance of centrifugal compressor diffusers Part 2: Straight channel diffusers. Proceedings, ASME International Gas Turbine and Aeroengine Congress and Exhibition, Stockholm, Sweden, ASME Paper 98-GT-474 (June 1998).

C7. Denton, J.D., Dawes, W.N. CFD for turbomachinery design. Proceedings, Institution of Mechanical Engineers Conference on the Successful Exploitation of CFD in Turbomachinery Design, London (December 1997).

C8. Denton, J.D., Xu, L. Understanding three-dimensional flows in turbomachinery. Computational Fluid Dynamics '98: Proceedings, European Community on Computational Methods in Applied Sciences (ECCOMAS) Conference, Athens, Greece (September 1998), 2, 57-70 (Wiley, 1998).

C9. Fillipenco, V.G., Greitzer, E.M., Deniz, S., Johnston, M., Cumpsty, N.A. Effects of inlet flow field conditions of the performance of centrifugal compressor diffusers Part 1: Discrete-passage diffusers. Proceedings, ASME International Gas Turbine and Aeroengine Congress and Exhibition, Stockholm, Sweden, ASME Paper 98GT-473 (June 1998).

C10. FRIEDRICHS, S., HODSON, H.P., DAWES, W.N. Aerodynamic aspects of endwall film-cooling. Transactions of the ASME, Journal of Turbomachinery, 119, (4), 786-793 (1997).

C11. Friedrichs, S., Hodson, H.P., Dawes, W.N. The design of an improved endwall film-cooling configuration. Proceedings, ASME International Gas Turbine and Aeroengine Congress and Exhibition, Stockholm, Sweden, ASME Paper 98-GT-483 (June 1998).

C12. Hodson, H.P. Bladerow interactions in low pressure turbines. In: Blade Row Interference Effects Axial Turbomachinery Stages. VKI Lecture Series 1998-02 (Von Karman Institute for Fluid Dynamics, 1998).

C13. Hodson, H.P., Dawes, W.N. On the interpretation of measured profile losses in unsteady wake-turbine blade interaction studies. Transactions of the ASME, Journal of Turbomachinery, 120, (2), 276-284 (April 1998).

C14. Horlock, J.H. The effect of heat exchanger effectiveness and exergy loss in the estimation of cycle efficiency. Proceedings, ASME International Gas Turbine and Aeroengine Congress and Exhibition, Stockholm, Sweden, ASME Paper 98-GT-352 (June 1998).

C15. Horlock, J.H. The evaporative gas turbine (EGT) cycle. Transactions of the ASME, Journal of Engineering for Gas Turbines and Power, 120, (2), 336-343 (April 1998).

C16. Joo, W.G., Hynes, T.P. The application of actuator disks to calculations of the flow in turbofan installations. Transactions of the ASME, Journal of Turbomachinery, 119, (4), 733-741 (1997).

C17. Joo, W.G., Hynes, T.P. The simulation of turbomachinery blade rows in asymmetric flow using actuator disks. Transactions of the ASME, Journal of Turbomachinery, 119, (4), 723-732 (1997).

C18. Khalid, S.A., Khalsa, A.S., Waitz, I.A., Tan, C.S., Greitzer, E.M., Cumpsty, N.A., Adamczyk, J.A., Marble, F.E. Endwall blockage in axial compressors. Proceedings, ASME International Gas Turbine and Aeroengine Congress and Exhibition, Stockholm, Sweden, ASME Paper 98-GT-188 (June 1998).

C19. KONRAD, W., BREHM, N., KAMEIER, F., FREEMAN, C., DAY, I.J. Combustion instability investigations on the BR710 jet engine. Transactions of the ASME, Journal of Engineering for Gas Turbines and Power, 120, (1), 34-40 (1998).

C20. Schulte, V.S., Hodson, H.P. Unsteady wake-induced boundary layer transition in high lift LP turbines. Transactions of the ASME, Journal of Turbomachinery, 120, (1), 28-35 (January 1998).

C21. Slater, S.A., Young, J.B. The calculation of inertial particle transport using an Eulerian formulation. Proceedings, ASME Fluids Engineering Division Summer Meeting, Washington, DC, USA, Paper FEDSM98-5007 (June1998).

C22. Taylor, J., Hynes, T.P., Hercock, R.G. The development and application of methods for predicting lift fan installed performance. Proceedings, Royal Aeronautical Society International Powered Lift Conference, London, 12.1-12.11 (September 1998).

C23. Wallis, A.M., Denton, J.D. Comparison of design intent and experiemental measurements in a low aspect ratio axial flow turbine with three-dimensional blading. Proceedings, ASME International Gas Turbine and Aeroengine Congress and Exhibition, Stockholm, Sweden, ASME Paper 98-GT-516 (June 1998).

C24. White, A.J., Young, J.B. Loss measurements and interpretation of Pitot pressures in two-phase vapour-droplet flow. Experimental Thermal and Fluid Science, 15, (3), 279-287 (1997).

C25. Zhong, S., Kittichaikarn, C., Hodson, H.P., Ireland., P.T., A study of unsteady wake-induced boundary-layer transition with thermochromic liquid crystals. Proceedings, 4th Institution of Mechanical Engineers International Conference on Optical and Data Processing in Heat and Fluid Flows, London, Paper C541/012/98 (April 1998).

C26. Zhong, S., Kittichaikarn, C., Hodson, H.P., Ireland, P.T. Visualisation of turbulent spots under the influence of adverse pressure gradients. Proceedings, 8th International Symposium on Flow Visualisation, Italy (September 1998).

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Last modified: October 1999