Numerical investigations of the flow mechanisms in a subsonic compressor rotor with axial-skewed slot

By applying a concept similar to 'domain scaling' treatment often used in multi-stage turbomachinery flow field to the interface between the rotor blade passage and end-wall treatments, a series of computational studies were carried out to understand the physical mechanism responsible for improvement in stall margin of a modern subsonic axial-flow compressor rotor due to the axial-skewed slot casing treatment. Particular attention was given to examining the interaction between the rotor tip flow and the axial-skewed slot. In order to validate the multi-block model applied in the rotor blade end-wall region, the computational results for the modern subsonic compressor rotor both with and without axial-skewed slot casing treatment were correlated with available experimental test data. The computed results agree fairly well with the experimental data, and the computations are then used to describe the interaction between the rotor tip flow and axial-skewed slot. Detailed analyses of the flow visualization at the tip have exposed the different tip flow topologies between the cases with axial-skewed slot and with untreated smooth wall. It was found that the primary stall margin enhancement afforded by the axial-skewed slot casing treatment is a result of the tip flow manipulation. 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 physical mechanisms responsible for extending the compressor stall margin.