MODELING FOR CONTROL OF ROTATING STALL IN HIGH-SPEED MULTISTAGE AXIALCOMPRESSORS

Using a two-dimensional compressible flow representation of axial comp ressor dynamics, a control-theoretic input-output model is derived, wh ich is of general utility in rotating stall/surge active control studi es. The derivation presented here begins with a review of the fluid dy namic model, which is a two-dimensional stage stacking technique that accounts for blade row pressure rise, loss, and deviation as well as b lade row and interblade row compressible flow. This model is extended to include the effects of the upstream and downstream geometry and bou ndary conditions, and then manipulated into a transfer function form t hat dynamically relates actuator motion to sensor measurements. Key re lationships in this input-output form are then approximated using rati onal polynomials. Further manipulation yields an approximate model in standard form for studying active control of rotating stall and surge. As an example of high current relevance, the transfer function from a n array of jet actuators to an array of static pressure sensors is der ived. Numerical examples are also presented including a demonstration of the importance of proper choice of sensor and actuator locations, a s well as a comparison between sensor types. Under a variety of condit ions, it was found that sensor locations near the front of the compres sor or in the downstream gap are consistently the best choices, based on a quadratic optimization criterion and a specific three-stage compr essor model. The modeling and evaluation procedures presented here are a first step toward a rigorous approach to the design of active contr ol systems for high-speed axial compressors.