Inviscid rotordynamic damping forces due to nonaxisymmetric tip clearance in turbines

An actuator disk analysis is used to examine dynamic characteristics of des tabilizing tip clearance excitation forces that arise in turbines with a wh irling rotor. The slope of the cross force vs whirling frequency indicates the amount of direct damping that, together with the cross stiffness, deter mines rotordynamic stability. Thus, damping characteristics are extracted f rom the dependence of lateral forces on the whirling velocity. The analysis results reveal an inviscid aerodynamic direct damping effect. Furthermore, the damping effect is seen to be entirety due to the azimuthal pressure as ymmetry or azimuthal flow redistribution. Ia addition, this study explores the sensitivity of such ideal damping effects to turbine design parameters such as flow coefficient and axial blade gap.