Experimental Investigation of Impeller-Diffuser Interaction

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)
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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

Jet
Wake
PS
SS
Dean and Senoo (1960), Eckardt (1976) Krain
(1981)
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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

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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)

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Impeller-Diffuser Interaction (contd)

• Radial Gap
• Too small increase backflow, Cumpsty and Inoue
  (1984)
• Too large less mixing-out of jet-wake Gallus et
  al. (2003)

9
Motivation

• Why study impeller-diffuser interaction when
  numerous studies have been done?
• All configurations are different

• 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

Picture courtesy of Douglas Roberts (PWC)
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
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Purpose of SCR

• CFD
• Experimental validation of results obtained on
  SCR
• Seeding flow distribution, flow patterns, etc

• 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

Picture courtesy of Douglas Roberts (PWC)
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SCR
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Impeller Diffuser
Close-up of impeller
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Optical Access
10mm diameter
15mm diameter
Upstream Impeller Blades
Blade passages hub side
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Seeding Ports
Six Ports
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SCR Specifications

• Outlet Ma 0.85
• Total length 2.0 m
• Total height 1.4 m
• Similar physical dimensions of full-scale rig

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CFD Analysis

• ICEM CFD 10.0 with CFX 10.0

Mesh 1.1 million tetrahedral 0.2 million prism
element mesh

• SST k-? model

Boundary Conditions Inlet Ptotal 172.4
kPa Ttotal 288.15 K Outlet
Pstatic 101.3 kPa
mexpected 0.245 kg/s mCFX 0.242 kg/s
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Mach Number Contour Plot

• Impeller-diffuser only
• Region of high velocity in left most passage
• Obtaining close to desired Ma of 0.85 at
  impeller exit

50 blade height
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Flow Behaviour

• 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

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Flow Behaviour
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Blade Passages
Migration of high velocity region to shroud
suction-side and vice versa
Flow behaviour similar in passages up to outlet
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Pressure Contour Plot

• impeller-diffuser only
• Typical blade suction/pressure behaviour
• Corresponding region of low pressure in left
  most passage

Suction side
Pressure side
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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 PWC

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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

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Thank You

• Questions?