Rotordynamic effects of compressor rotor-tip clearance asymmetry

Rotordynamic effects caused by nonaxisymmetric rotor-tip clearance in an ax ial compressor stage have been analyzed. Two coupled actuator disc analyses are carried out at blade (meridional plane) and radius (radial plane) scal es, Continuity, axial, and tangential momentum equations are used to connec t upstream and downstream hows across the compressor stage, and a small per turbation analysis is used to obtain flowfield nonuniformities. Predictions indicate the following. Relative to the passage flow, the flow associated with the rotor-tip clearance is axially retarded and tangentially underturn ed. Furthermore, the compressor blades near the smaller tip gap are more hi ghly loaded. Thus, the tangential force asymmetry promotes a backward whirl . However, the pressure asymmetry caused by azimuthal flow redistribution i nduces a forward whirl. The net result is a backward-whirling force whose m agnitude is much smaller than that of the forward-whirling force found in t urbines.