A type of trapped vortex casing treatment (CT) was designed

using pressure difference between suction side at front and pressure side at rear of passage to drive fluid flowing back. Boundary flow was sucked into slot at rear of passage

then injected into main flow at front of passage. During this process

momentum of the fluid in the leakage was increased

and then the stall margin of the blade was enhanced. The loss of mixing is decreased by adjusting the direction of suction and injection to the direction of main flow. Also the size of CT in axial direction is inside the blade dimention

which means this CT could be used in each stage of multistage compressors

without overlapping with stators. Numerical simulation was used to evaluate the effectiveness of this CT. Result shows that this CT could increase the stall margin 17.39% of a transonic compressor rotor without compromise on efficiency.