Pressure Oscillations Occurring in a Centrifugal Compressor System With and Without Passive and Active Surge Control

A study of pressure oscillations occurring in small centrifugal compressor systems without a plenum is presented. Active and passive surge control were investigated theoretically and experimentally for systems with various inlet and discharge piping configurations. The determination of static and dynamic stability criteria was based on Greitzer’s (1981) lumped parameter model modified to accommodate capacitance of the piping. Experimentally, passive control using globe valves closely coupled to the compressor prevented the occurrence of surge even with the flow reduced to zero. Active control with a sleeve valve located at the compressor was effective but involved a significant component of passive throttling which reduced the compressor efficiency. With an oscillator connected to a short side-branch at the compressor, effective active control was achieved without throttling. Both methods of active control reduced the flow rate at surge onset by about 30%. In general, the experiments qualitatively confirmed the derived stability criteria.