Annular Diffuser Performance for an Automotive Gas Turbine

Abstract

A series of experimental tests and computational analyses are reported for two automotive gas turbine diffusers. The diffusers include an interstage and an exhaust diffuser plus collector. The diffuser models were tested at Reynolds numbers and inlet blockage levels characteristic of the engine operating conditions. A rig test of the interstage diffuser is also reported. Inlet swirl and Mach number were systematically varied in the model tests. Good recovery was found for each diffuser at zero swirl. Recovery degraded at high swirl for the interstage diffuser. The exhaust diffuser with a double discharge collector showed little sensitivity to inlet swirl. Flow visualization indicates that the interstage diffuser was separated at modest swirl levels, at least in the model test. Pressure recovery in the rig (with upstream rotor and downstream stator) was found to be greater than in the model test (using “clean” inlet conditions). Comparisons between measured wall pressures and calculations provide further basic insights.