The Numerical Investigationof Casing Treatmenton Transonic Compressor

As a simple and effective passive control technology,the use of casing treatment is becoming increasingly widerin improving compressor stability margin.So to speak,casing treatment is one of the most widely used methodsof stall margin improvementsin the field of turbomachinery.However,over the years,the design of casing treatment approach mainly depends on experience,lack of uniform guidelines.In order to analysis the predisposing factors of transonic compressor stall mechanism,a three-dimensional steady/unsteady calculation is used,focus on tip flow field.It has different internal flow stall mechanism in different speed for this transonic compressor.In the design speed,the rotor is in transonic flow,the main mechanism of trigger the compressor’s flow instability is accumulation in the face of pressure sidepush the passage shock out of the leading edge of the blade tip caused by the leakage vortex breakdown.However,in non-design speed,the rotor is in subsonic flow,accumulation caused by the leakage vortex breakdown and the large area flow separation in the suction side caused by larger angle of attack work together to cause rotating stall,the main roleis separation in the suction side.On the basis of analysis the compressor rotating stall,I will use circumferential grooves and axial slots to,and investigate the effect of stall margin improvements and the impact on the stall for different casing treatment structures under transonic compressor’s different speed.Circumferential groovescan improve the stability margin under different speeds.There are three main areas on the flow field: First,change the leakage vortex trajectory to make it more biased on the suction surface,it can improve axial flow capacity.Second,the low energy fluid can be pumped out by the hole effect of circumferential grooves.Thirdly,suppress separation in thetrailing edge of suction side.Throughing the study of the wide groove and narrow grooveI find that narrow and dense grooves can more effectively guiding gap leakage along the circumferential movement.Narrow and more grooves has better effect in improving the stall margin than wide and less grooves under the same processing area.The mechanism of axial slots is different from circumferential grooves.It is better for the stability when the trailing edge of the slot is just located in the area that the blocking caused by leakage vortex.Compared axial skewed slots with bend skewed slots,bend skewed slots is better on stability,and it has less effect on efficiency.This is mainly due to bend skewed slots is more responsive to the direction of airflow,it has large inflow and injected airflow,smallerinjected velocity,better air circulation in the slot,better improvementto the stability margin,and little impact on the efficiency.For transonic compressor,the reason that axial slots can improve the stability margin is slots can inhibit the development of leakage vortex and reduce blockingin different speeds.