A Rational Basis for Circumferential Distortion Index Formulation.

NASA has recently published data on the effects of temperature and pressure distortion on the stability of axial-flow compressors. Theoretical predictions of compressor instability based on vorticity do not explain the observed compressor stability of the NASA tests. Description of distorted flow by vorticity is extended by a simplified model which incorporates vortex sheets and influence coefficients. To determine the upstream influence of the compressor on flow field distortion, a model using parallel compressor theory, experimental data from NASA and a pressure ratio equation derived by Hill and Peterson is formulated. The model correctly predicts compressor blade loading calculated by Carta. This new model accounts for upstream effects of the compressor and shows that the vorticity model by itself is incomplete. Incorporation of the new model into a distortion index based on radial vorticity and total pressure change is proposed and discussed. (Author)