Mechanism of axial-flow compressor stall margin improvement associated with bend skewed slots casing treatment

The bend skewed slot casing treatment has the potential to significantly extend the stall margin of the compressor with minimal or no loss in efficiency. In order to uncover the working mechanism by which bend skewed slots casing treatments improve stall margin and also the flow mechanisms the bend skewed slots casing treatments differ from axial skewed slots casing treatment, a time accurate 3-dimentional numerical simulation was performed for the subsonic axial-flow compressor rotor both with bend skewed slot casing treatment and axial skewed slot casing treatment. The numerical results agreed well with experimental data for the global performance. Detailed analyses of the flow visualization at the tip have exposed the different tip flow topologies between the cases with casing treatment and with untreated smooth wall. It was found that the repositioning of the tip vortex trajectory further towards the trailing edge of the blade passage and delaying the movement of incoming/tip clearance flow interface to the leading edge plane are the exact mechanism of stall suppression imposed by bend skewed slot casing treatment.