Simulation and Active Control of Surge Instability in Axial Flow Compressors

Abstract

A one-dimensional unsteady model capable of analyzing various arrangements of turbomachinery components has been developed. Surge disturbance propagation has been captured within a turbojet engine. It is demonstrated that these instabilities can be stabilized by the use of active control strategies such as air bleeding and air injection. The effect of variable area diffuser is also studied. Two types of active control systems are considered: steady and unsteady. In steady case, mass is removed at a fixed rate from the diffuser or interstage, or mass is injected at a fixed rate into the first stage of compressor. In unsteady control, the rate of bleeding or injection is linked to the amplitude and frequency of the upstream pressure disturbances. Results show that both steady and unsteady strategies eliminate surge disturbance and suppress the instabilities. Therefore, they extend the stable operating range of compressor. It is observed that injection can reduce the amount of bleeding air. It is also shown that smaller amount of compressed air need to be removed with the unsteady control, as compared to steady case. Variable area diffuser is shown to be able of suppressing surge instabilities. Perturbations of inlet total pressure or temperature may lead the compressor to stall. Active control of instabilities caused by sinusoidal perturbations of inlet total pressure is also investigated in the present study.