A THEORETICAL AND EXPERIMENTAL INVESTIGATION OF A GAS-OPERATED BEARING DAMPER FOR TURBOMACHINERY .1. THEORETICAL-MODEL AND PREDICTIONS

This is the first (Part I) of two papers describing recent results of the research program directed at developing a vibration damper suitabl e for high-temperature turbomachinery applications. It is expected tha t such dampers will replace squeeze-film dampers, which use oil as the working fluid and have limitations at higher temperatures. A novel ga s-operated bearing damper has been evaluated analytically and experime ntally for its damping characteristics. A theory based on the isentrop ic assumptions predicts the damper performance characteristics reasona bly well. A maximum damping level of 2311 N-m/s (13.2 lb-s/in.) at a f requency of 100 Hz was measured with a single actuator of the gas damp er. Since many such actuators could be placed circumferentially around the squirrel cage, considerable damping levels can be realized. The s tudy also shows that significantly higher damping levels can be achiev ed by modifying the current design. Part I describes the theoretical m odel that has been developed based on isentropic assumptions. This mod el is an improved version of the previous theory (Vance et al., 1991) and includes the supply groove effects, dynamic area changes of the in let feeding holes, and the effects of flow choking on damper behavior. The governing equations are derived and theoretical predictions using these equations have been made for two hardware designs that were exp erimentally investigated (see Part II for experimental results).