Abstract
,The influence of a downstream stator row on the measurement of compressor rotor performance has been examined using a two-dimensional computational fluid dynamic (CFD) code backed by laser anemometry data on a transonic fan stage. The upstream potential influence of the stator causes unsteady circulation about the rotor blades which is a function of the rotor circumferential position. This, in turn, results in a nonuniform circumferential pattern of time-averaged temperature and pressure in the stationary frame. A relatively fast calculational procedure using a linearized, potential flow approach coupled with an analytical theory relating the temperature and pressure variations to the circulation perturbation is developed and shown to give good agreement with the numerical calculations. The results of a parametric study show that the magnitude of this effect is a strong function of rotor-stator blade row spacing and relative blade counts. The effects range from negligible for large spacings typical of high bypass ratio fans, to several percent of the stage pressure and temperature rise for closely spaced blade rows typical of high compressors. Because the temperature and pressure perturbations are in spatial phase, the net effect on measured rotor efficiency is negligible so long as the pressure and temperature measurements are made in the same location relative to the stators. If they are not, errors of ±1.5% can result. The effects of axial position and stator loading are shown to be relatively small.
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