Asymmetric Distortion Generation in a Variable Height Annulus

Abstract

POROUS screens were placed in the compressor intake to create quasisteady pressure maldistributed inlet flows. This study was aimed at creating a single-lobe circumferential sine-wave velocity profile with no radial components at the compressor inlet. A method relating screen blockage to predicted velocity levels was devised. The method yields velocity levels close to those for which the screen was designed. Contents Quasisteady pressure maldistributed compressor inlet flows are normally created during testing by the inclusion of porous screens in the compressor intake, but interactions between a row of compressor rotor blades and upstream placed screens in such experiments can alter the shape of the generated distortion.l Suppression of this effect may be realized by remote positioning of the screen upstream of the compressor leading-edge plane. Often, an intake may not be a constant annulus, so flow differences between the compressor leadingedge plane and the plane of the screen call for differences in the screen design whose generated distortion is itself modified in passing through the annulus to the compressor. The aim of this study was to present to a compressor inlet a single-lobe circumferential sine-wave velocity profile with no radial components, the distortion being generated remotely upstream in a duct dissimilar to the annulus at the compressor intake. Based upon small perturbation assumptions, a method of screen design is proposed which superimposes a generated distortion upon the undistorted potential flow solution of the developed annulus. The example used was a bellmouth and nose-bullet sited coaxially close to the compressor leadingedge plane and separated only by a short length of the constant height annulus. The screen was set at the bellmouth intake, perpendicular to the axial direction. While this example used symmetrical ducting, the principles involved could be applied to a nonsymmetrical installation.