Compressor Modeling and Active Control of Stall/Surge

The Moore-Greitzer formulation for compressor dynamics is extended to symmetric-flow compressor map shapes other than the cubic map treated by Moore and Greitzer. Two families of curves, odd-polynomial and even-polynomial families, are defined that provide a wide range of shapes in the stable-flow regime, and the amplitudes of flow asymmetry in steady rotating stall are calculated for members of both families. These calculations show that compressors capable of operating stably over a wide range of gas flows are likely to encounter larger asymmetry components when a stall does occur than compressors with narrower stable-flow regions. The paper also details a control strategy based on sensing of asymmetric axial flow components and the rate of change of mean flow, and shows that controlled bleed of high pressure air based on such measurements can be used to supress both stall and surge oscillations. This strategy provides suppression of oscillations while other control actions are taken to move from an unstable operating condition to a stable situation.