Unsteady Flow Phenomena in Discrete Passage Diffusers for Centrifugal Compressors
Final rept. 8 Jul 1990-8 Jan 1994
MASSACHUSETTS INST OF TECH CAMBRIDGE GAS TURBINE LAB
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Research is described on the fluid dynamic behavior of high performance diffusers for centrifugal compressors, with particular application to small gas turbine engine applications. Using a unique swirl generator, experiments have been carried out to define the performance and stall onset behavior of a modern discrete passage diffuser as a function of inlet conditions. Two diffusers were examined, one with 30 passages and one with 38 passages. Inlet blockage and axial asymmetry were varied over Mach numbers up to unity and over a range of inlet swirl angles. Diffuser pressure recovery and operating range were calculated using traverse measurements made upstream of the diffuser. It was found that the performance of the diffuser under different inlet conditions could be expressed to a high degree of accuracy as a single curve of non-dimensional static pressure recovery coefficient, based on availability averaged inlet stagnation pressure, and momentum-averaged inlet flow angle. Unsteady pressure measurements showed that the diffuser entered rotating stall at reduced flow rates. No long wavelength stall precursor was determined from the measurements.
- Jet and Gas Turbine Engines