Experimental investigation of the casing treatment effects on steady and transient characteristics in an industrial centrifugal compressor

Abstract

In this paper, a method of holed casing treatment is put forward and applied to an industrial centrifugal compressor. A series of experimental investigations are conducted to study the effects of casing treatment on steady and transient performance of the compressor. Dynamic pressure is monitored under stable operating point and surge occurrence condition at following positions: two ends of the treated holes, 37%-chord impeller tip position and the vaneless diffuser. By use of the casing treatment, the surge margin of the compressor is increased by about 10%Qdesign with negligible decrease in efficiency. Pulsating pressure change is taken as an indicator for evaluating the flow direction in the hole. Near surge point, when the static pressure of the bleeding port is larger than the turning point, a sudden increase in pulsating pressure indicates that the bleeding flow occurs. Near choke side, when the static pressure of the turning point is larger than the bleeding port, a severe change in pulsating pressure indicates that the bypass flow occurs. Signal analysis of the dynamic pressure at surge occurrence shows that the compressor stalls with a modal inception rather than a spike wave no matter casing treatment is applied or not. The travelling speed of the stall cell found in the compressor with casing treatment is faster than that with solid casing. The occurrence of modal precursor wave is delayed with casing treatment.