Exploring mechanism of flow instability and stall margin enhancement of a subsonic axial-flow compressor due to casing treatment

The role of complex tip flow mechanisms on flow instability in a subsonic axial-flow compressors has been assessed using time-accurate single blade passage computations and experimental measurement. Systematic studies of the coupled flow through a subsonic compressor rotor and two various end-wall treatments were carried out using state-of-the-art multi-block flow solver. Detailed analyses of the flow visualization at the rotor tip have exposed the different tip flow topologies between the cases with treatment casing and with untreated smooth wall. It was found that the blockage zone which is positioned about pressure side of adjacent blade play an essential role on the loss flow instability, this area is mainly a result of the motion of the tip leakage vortex moving upstream of the rotor passage as the mass flow rate decreases for the subsonic axial-flow compressor. Compared to the smooth wall case, the treated casing significantly dampen or absorb the blockage near the upstream part of the blade passage caused by the upstream movement of tip leakage flow and weakens the roll-up of the core vortex. These mechanisms prevent an early spillage of low momentum fluid into the adjacent blade passage, therefore delay the onset of rotating stall.