1. Experimental Investigation of Impeller-Diffuser Interaction Rita Patel, Eric Savory and Robert Martinuzzi

2. Outline Background Motivation Current Work –Design of experimental rig –CFD analysis Results and discussion Conclusions Future Work

3. Terminology Cumpsty (1978)

4. Types of Impellers and Diffusers Impellers Radially ending Backswept Pre-swirl Above w/splitter blades Diffusers Vaneless Vaned –Radial –Wedge Discrete-passage Pictures courtesy of Compressor Branch NASA Glenn Research Center

5. Radial Impeller Discharge Increasing BL on shroud-suction side due to curvature –Separation –Wake on shroud- suction side –Jet displaced to hub- pressure side Dean and Senoo (1960), Eckardt (1976) & Krain (1981) Jet Wake SS PS

6. Diffuser Inlet Large inlet distortions due to impeller wake –Angle and velocity fluctuations Distortions have least effect in passage diffusers than vaned, and most in vaneless Mixing-out of jet-wake stimulated by presence of vanes

7. Impeller-Diffuser Interaction Vanes –Stationary vanes produce unsteady pressure disturbances to rotating impeller, Gallus et al. (2003) –Velocity fluctuations of 17-20% in vaneless space, Krain (1981) –Cause of backflow to impeller, Cui (2003) –Decrease traveled distance of impeller discharge distortion, Ghiglione et al. (1998)

8. Impeller-Diffuser Interaction (cont’d) Radial Gap –Too small = increase backflow, Cumpsty and Inoue (1984) –Too large = less mixing-out of jet-wake Gallus et al. (2003)

9. Motivation –This project will lead into the study of a tandem-bladed impeller coupled with a fishtail diffuser –Study the magnitude and effect of pressure disturbances in vaneless space –Validate previously obtained CFD results Why study impeller-diffuser interaction when numerous studies have been done? All configurations are different Picture courtesy of Douglas Roberts (P&WC)

10. Current Work Design a test facility (SCR*) that simulates a typical radial impeller exit flow field in steady state through a non- rotating cascade configuration –5 stationary radial impeller blades –Diffuser with 5 flat plate splitters –Pipe to provide required inlet flow Obtain LDV data of flow field *Stationary Cascade Rig

11. Purpose of SCR Better understanding of how to apply LDV technique to a full-scale rig –Test use of very small optical access ports –Type of seeding for this specific flow CFD – Experimental validation of results obtained on SCR Seeding flow distribution, flow patterns, etc… Picture courtesy of Douglas Roberts (P&WC)

12. SCR

13. Impeller + Diffuser Close-up of impeller

14. Upstream Impeller BladesBlade passages ‘hub side’ Optical Access 10mm diameter 15mm diameter

15. Seeding Ports Six Ports

16. SCR Specifications Outlet Ma: 0.85 Total length: 2.0 [m] Total height: 1.4 [m] Similar physical dimensions of full- scale rig

17. CFD Analysis ICEM CFD 10.0 with CFX 10.0 Mesh: 1.1 million tetrahedral + 0.2 million prism element mesh Boundary Conditions: Inlet: P total = 172.4 [kPa] T total = 288.15 [K] Outlet: P static = 101.3 [kPa] SST k-ω model m expected = 0.245 kg/s m CFX = 0.242 kg/s

18. - Impeller-diffuser only - Region of high velocity in left most passage - Obtaining close to desired Ma of 0.85 at impeller exit Mach Number Contour Plot 50% blade height

19. Shock wave at trailing edge of each blade Passage width increasing, while height decreasing Greater shock wave in left passage as result of diffuser sidewall Flow Behaviour

21. Blade Passages Flow behaviour similar in passages up to outlet Migration of high velocity region to shroud suction- side and vice versa

22. Pressure side Suction side -impeller- diffuser only - Typical blade suction/pressure behaviour - Corresponding region of low pressure in left most passage Pressure Contour Plot

23. Conclusions From CFX results –Presence of separation in diffuser –No separation in impeller –Good flow pattern agreement between blade passages Close agreement between theoretically calculated and CFX values at boundaries SCR will provide a good understanding of how to apply LDV technique in a high-speed, highly- confined, compressible flow

24. Future Work Experimental –Measurements in SCRF –Compare with current CFD results Computational –Track seeding particles Apply LDV technique and CFD model on full- scale rig at P&WC

25. Acknowledgements Advanced Fluid Mechanics Research Group –http://www.eng.uwo.ca/research/afm/default.htm Kevin Barker and Doug Phillips –University Machine Shop Rofiqul Islam –University of Calgary Suresh Kacker, Douglas Roberts, Feng Shi and Peter Townsend –Pratt and Whitney Canada

26. Thank You Questions?