Measurement versus predictions of rotordynamic coefficients of seal with swirl brakes

Abstract

Seal rotordynamic coefficients have a primary influence on stability response of high-performance turbomachinery. The swirl brake is one approach to improve the rotordynamic characteristics of seals. Although swirl brakes have been used successfully in practice, the experimental studies dealing with the rotordynamic coefficients associated with different swirl brake geometries as well as operating conditions are very spare. The present research investigates the effects of the swirl brakes on the rotordynamics of labyrinth seals. Experiments are presented to identify the stiffness and damping force coefficients using an improved impedance method based on unbalanced synchronous excitation method on a rotating test rig. Several design parameters, such as swirl brake density and length have been considered and also the operating conditions (inlet/outlet pressure ratio and rotating speed) are accounted for. Test results demonstrate the pronounced favorable influence of the swirl brake to effectively reduce the cross-couple stiffness and increase the direct damping for variable conditions. It is believed that the results of this study will assist in improving the design of annular seals.