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Measurements of the Effects of Periodic Inflow Unsteadiness on the Aerodynamics of a Fishtail Diffuser

[+] Author Affiliations
M. I. Yaras, P. Orsi

Carleton University, Ottawa, ON, Canada

Paper No. GT2002-30455, pp. 829-840; 12 pages
  • ASME Turbo Expo 2002: Power for Land, Sea, and Air
  • Volume 5: Turbo Expo 2002, Parts A and B
  • Amsterdam, The Netherlands, June 3–6, 2002
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 0-7918-3610-X | eISBN: 0-7918-3601-0
  • Copyright © 2002 by ASME


This study examines the effects of periodic inflow unsteadiness on the flow development through fishtail diffusers utilized on small gas-turbine engines. The periodic unsteadiness is due to the distortion of the flow in the peripheral direction at the exit of the centrifugal compressor impeller, caused by the jet-wake type of flow discharging from each passage of the impeller. The study consists of detailed measurements in a large-scale fishtail diffuser rig with a geometry that is typical of those used in small gas turbine engines. An unsteady-flow generator is used to approximate the type of diffuser-inflow conditions that exist at the exit of centrifugal compressor impellers. Detailed measurements of the transient velocity field have been performed at the inlet and at four cross-sectional planes throughout the diffuser using a miniature 4-wire probe. These measurements involve frequencies of inflow unsteadiness corresponding to design as well as off-design operating conditions. The measured velocity field is analyzed in a time-averaged sense and in the context of previously-performed steady-flow measurements. Results show significant effects of inflow unsteadiness at lower frequencies on the flow field in the diffuser, which translates into a substantial impact on the pressure recovery of the diffuser. In addition to providing insight into the physics of this flow, the experimental results presented here constitute a detailed and accurate data set that can be used to validate computational-fluid-dynamics codes for this application.

Copyright © 2002 by ASME



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