Inviscid Rotordynamic Damping Forces due to Non-Axisymmetric Tip Clearance in Turbines
An actuator disk analysis is used to examine dynamic characteristics of destabilizing tip clearance excitation forces that arise in turbines with a whirling rotor. The slope of the cross force vs whirling frequency indicates the amountofdirectdamping that,togetherwith thecross stiffness,determinesrotordynamicstability.Thus, damping characteristics are extracted from the dependence of lateral forces on the whirling velocity. The analysis results reveal an inviscid aerodynamicdirect damping effect. Furthermore, thedamping effect is seen to be entirely due to the azimuthal pressure asymmetry or azimuthal e ow redistribution. In addition, this study explores the sensitivity of such ideal damping effects to turbine design parameters such as e ow coefe cient and axial blade gap.