Experimental evaluation of the high-to-low speed transformation process for a highly loaded core compressor stage

Abstract

A set of low speed blading has been designed lo represent an embedded stage from the DERA C147 high speed research compressor. The aim of the design was to undertake a careful high-to-low speed transformation of the geometry of a high speed stage and evaluate the transformation process through comparing detailed flow measurements taken in both the high and low speed environments. The high-to-low speed transformation process involves compromises due to both geometric and aerodynamic constraints. Geometric constraints include the parallel annulus of the low speed compressor and also its size and power which restrict the Reynolds number that can be achieved. Aerodynamically the high speed blades have to be subsonic and the effects of Mach number on loss buckets and boundary layer development limit the extent to which a full high-to-low speed match is possible. The low speed blading has been lested at Cranfield University's 4-stage research compressor facility. Detailed traverse measurements were taken at rotor and stator exit along with blade surface static pressure measurements and oil flow visualisation. These, along with previous traverse measurements from the C147 compressor, have been used to show that a good comparison of pressure, flow angle, and endwall loss distributions can be achieved despite the compromises inherent in the transformation process. However some interesting differences were apparent and these are discussed. In addition, 3D flow calculations have been performed on both the rotor and stator using measured inlet conditions. These predictions model the endwall comer flow well. However, further work is needed to obtain better modelling of the clearance flow of both blade rows.