The effect of inlet circumferential maldistribution on an axial compressor stage

Abstract

This report describes tests on a single compressor stage with circumferentially non-uniform inlet conditions. The stage was a model of the first stage of a typical modern aircraft-engine compressor, and the tests were planned as part of an investigation into the surge behaviour of compressors with inlet flow maldistribution. It was found that with a roughly rectangular inlet velocity distribution of amplitude ± 25 per cent of the mean value, the surge flow instead of showing an expected increase was almost unchanged, being in fact slightly reduced. The efficiency fell greatly, with an accompanying small drop in temperature-rise coefficient. The velocity profile was distorted and its amplitude greatly decreased at the outlet of the stage. These results are important in that they suggest that the surge of the first stage is not the primary factor in determining the surge of a multi-stage compressor. It would appear that the primary effect of maldistribution is to decrease the efficiency of the first stage or stages, and thus alter the stage matching at the surge flow, which is, however, mainly determined by the later stages. The maldistribution will probably have disappeared at these later stages, which will thus exhibit their normal characteristics. These conclusions are supported by analysis of multi-stage compressor performance and by theoretical considerations.