The Prediction of Steady, Circumferential Pressure and Temperature Distortions in Multistage Axial Flow Compressors

A small perturbation theory is presented for the prediction of the decay of steady circumferential pressure, temperature and velocity distortions in multistage axial flow compressors. The mathematical model which is employed replaces the blade rows of the compressor by actuator discs. A closed solution for the linearized equations describing the two-dimensional, inviscid and compressible flow between the discs is derived and appropriate matching conditions at the discs (assuming a quasi-steady blade response) are determined. An efficient calculation procedure is presented which allows the rapid computation of the distortion development through any compressor configuration, i.e., through any combination of rotors, stators, and axial clearances including the core engine compression system. The theory can be applied to the mean section of the compressor or separately from stream surface to stream surface. Due to the assumption of a two-dimensional flow, however, it is restricted to purely circumferential distortions in compressors with sufficiently high hub-to-tip ratios where radial flow redistributions can be expected to be small. The validity of the small perturbation theory is demonstrated by comparing the theoretical results with experimental data. In addition, the theory is used to study the effect of Mach-number and flow rate on the decay of the distortions through two compressor configurations. Suggestions are made on how to utilize the theory for the design of distortion-tolerant compressors.