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Unsteady Radial Transport in a Transonic Compressor Stage FREE

[+] Author Affiliations
P. A. Kotidis, A. H. Epstein

Massachusetts Institute of Technology, Cambridge, MA

Paper No. 90-GT-133, pp. V001T01A040; 12 pages
doi:10.1115/90-GT-133
From:
  • ASME 1990 International Gas Turbine and Aeroengine Congress and Exposition
  • Volume 1: Turbomachinery
  • Brussels, Belgium, June 11–14, 1990
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7904-7
  • Copyright © 1990 by ASME

abstract

Time-resolved radial transport has been measured in a transonic compressor rotor by injecting a thin sheet of tracer gas upstream of the rotor and then surveying the tracer concentration at the rotor exit. The simultaneous, co-located, high frequency response measurements of local tracer gas concentration, total temperature, and total pressure made downstream of the rotor showed that most of the fluid transported radially appears in the blade wakes and that this fluid has considerably higher entropy than the circumferential mean. Both inward and outward fluid transport along the span was observed (3.5% of the total throughflow moved toward the tip while 1.6% moved toward the hub). Tracer concentration and fluid total temperature and pressure varied considerably from wake to wake, even on multiple samplings of the same blade. The time mean spreading rate inferred from these measurements is in general agreement with previously reported studies on multi-stage low speed compressors and is well predicted by the method of Gallimore and Cumpsty. It is suggested that a vortex street in the blade wakes could be responsible for both the observed radial transport and the large wake to wake variability. A quasi-three-dimensional model of a vortex street wake was developed and shown to be consistent with the data. The model predicts all of the inward transport but only 20% of the outward transport. It is hypothesized that outflow in separated regions on the blade suction surface is responsible for the remainder of the transport toward the rotor tip. Since the entropy, as well as the mass of the fluid transported radially, was measured, an estimate of the redistribution of loss in rotor due to radial fluid transport could be made. This showed that the effect of radial transport in this rotor was to move substantial loss from the rotor hub to tip, implying that a conventionally measured spanwise efficiency survey may not accurately represent the performance of individual blade sections.

Copyright © 1990 by ASME
Topics: Compressors
This article is only available in the PDF format.

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