In turbocharger applications, bleed air near the impeller exit is often used for secondary flow systems to seal bearing compartments and to balance the thrust load on the bearings. There is experimental evidence that the performance and operability of highly-loaded centrifugal compressor designs can be sensitive to the amount of bleed air. To investigate the underlying mechanisms and to assess the impact of bleed air on the compressor dynamic behavior, a research program was carried out on a preproduction, 5.0 pressure ratio, high-speed centrifugal compressor stage of advanced design. The investigations showed that bleed air can significantly reduce the stable flow range. Compressor rig experiments, using an array of unsteady pressure sensors and a bleed valve to simulate a typical turbocharger environment, suggest that the path into compression system instability is altered by the bleed flow. Without the bleed flow, the prestall behavior is dominated by short-wavelength disturbances, or so called “spikes,” in the vaneless space between the impeller and the vaned diffuser. Introducing bleed flow at the impeller exit reduces endwall blockage in the vaneless space and destabilizes the highly-loaded vaned diffuser. The impact is a 50% reduction in stable operating range. The altered diffuser characteristic reduces the compression system damping responsible for long-wavelength modal prestall behavior. A four-lobed backward traveling rotating stall wave is experimentally measured in agreement with calculations obtained from a previously developed dynamic compressor model. In addition, a self-contained endwall blockage control strategy was employed, successfully recovering 75% of the loss in surge-margin due to the bleed flow and yielding a one point increase in adiabatic compressor efficiency.
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July 2009
Research Papers
Spike and Modal Stall Inception in an Advanced Turbocharger Centrifugal Compressor
Z. S. Spakovszky,
Z. S. Spakovszky
Gas Turbine Laboratory,
Massachusetts Institute of Technology
, Cambridge, MA 02139
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C. H. Roduner
C. H. Roduner
ABB Turbo Systems Ltd.
, Baden 5400, Switzerland
Search for other works by this author on:
Z. S. Spakovszky
Gas Turbine Laboratory,
Massachusetts Institute of Technology
, Cambridge, MA 02139
C. H. Roduner
ABB Turbo Systems Ltd.
, Baden 5400, SwitzerlandJ. Turbomach. Jul 2009, 131(3): 031012 (9 pages)
Published Online: April 10, 2009
Article history
Received:
December 21, 2007
Revised:
March 22, 2008
Published:
April 10, 2009
Citation
Spakovszky, Z. S., and Roduner, C. H. (April 10, 2009). "Spike and Modal Stall Inception in an Advanced Turbocharger Centrifugal Compressor." ASME. J. Turbomach. July 2009; 131(3): 031012. https://doi.org/10.1115/1.2988166
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