Model Development for Active Surge Control/Rotating Stall Avoidance in Aircraft Gas Turbine Engines

The focus of this paper is on the development of models for use in the design of active surge control/rotating stall avoidance systems in aircraft gas turbine engines. Model development is illustrated for the case of a single-spool, centrifugal compressor, turbojet engine currently housed within the LICCHUS experimental facility at Georgia Tech. This engine is equipped with high bandwidth fuel flow, nozzle area, and compressor discharge bleed area servos. The model developed for this engine is based on engine component steady state performance maps and unsteady quasi one-dimensional flow equations. The latter are rigorously developed herein. Special attention is paid to the assumptions underlying the model development, particularly those pertaining to the unsteady flow aspects of the model and its dynamic order. The resulting model has three control inputs, three states, and incorporates the dynamic linkage of the compressor and turbine through the spool. The three states are compressor mass flow, plenum pressure, and spool speed. Simulation results are given for the model which indicate that the model is capable of predicting and modeling surge phenomena. Because of its quasi one-dimensional nature, the model is not capable of predicting and modeling rotating stall per se. However, the model is capable of predicting and modeling the state of rotating stall as a condition of steady, greatly reduced, annulus-averaged compressor mass flow rate, and thus is adequate for the design of rotating stall avoidance systems. Additional simulation results are given which show the response of the model to the various control inputs.