Development of a body force description for compressor stability assessment

Abstract

This thesis presents a methodology for a body force description of a compressor with particular application to compressor stability calculations. The methodology is based on extracting blade forces from an axisymmetric flow description and reinterpreting the blade force as a body force acting throughout the fluid. A "blade force average," which translates a three dimensional flow into the axisymmetric description used in this methodology, is described. The methodology is demonstrated using flow fields from three dimensional computational fluid dynamics (CFD) to form body force distributions over the range of flow coefficients in which converged solutions can be obtained and using two dimensional CFD to extend the description to lower flows. The connection between specific flow features and the body force is described for a sample compressor, along with the effect of using averages other than the body force average when reducing the three dimensional flow to an axisymmetric description. To assess the body force modeling procedure, flow fields produced by using the body force as input to a compressor flow computation are presented and compared to the flow fields originally used to produce the body forces. While not conclusive, the comparison provides a positive indication that the body force modeling can be useful as part of a stall prediction procedure.