A DUAL FLOW HIGH MACH NUMBER CENTRIFUGAL COMPRESSOR FOR A SMALL GAS TURBINE APU

摘要

Small gas turbine auxiliary power units (APU's) of conventional load compressor type wherein the gas generator or core module directly drives a separate centrifugal load compressor are installed in aircraft and helicopters to supply both compressor air for main engine starting and air conditioning combined with shaft power to drive an electric generator. This paper describes the test development of a dual flow centrifugal compressor (DFC) where the impeller flow was split into two streams, the inner (hub) stream supplying compressed air to the gas generator core module, and the outer (DFB) bleed stream delivering a compressed air to the aircraft pneumatic power system. DFC development rig testing revealed that the hub or core stream satisfied compressor design requirements but that the DFB stream flowpath demonstrated unstable characteristics with decreasing efficiency as test speeds were increased. At the time of the development program in the early 1990's convergence difficulties were encountered with CFD attempts to corroborate the test results, and thus pinpoint plausible explanations, as a consequence a renewed upgraded 2010 CFD analysis of the dual flow compressor is presented herein confirming the test performance characteristics of both flow streams and the fundamental reason for poor DFB performance as excessive diffusion at high relative Mach numbers.