Numerical analysis of the circumferential grooves casing treatment in a counter-rotating axial flow compressor

The impact of the circumferential grooves casing treatment over the rear rotor (R2) in a counter-rotating axial flow compressor has been investigated based on numerical simulations. The main purpose is to understand the effects of grooved casing treatment on the unsteady flow behaviors and the corresponding mechanisms of the stability enhancement in the compressor. The results show that the interface between incoming main flow and tip leakage flow in R2 is pushed downstream obviously and the flow stability is enhanced with grooved casing treatment. The compressor performance at near stall condition is also improved remarkably. The blade loading below the grooves, the incidence angle near the blade tip and the backward axial momentum flux injected into main flow passage through the tip gap are all reduced, which is beneficial to the stall margin improvement. Frequency analysis near the blade tip of R2 indicates that the oscillations with lower frequency are suppressed by the casing grooves and the fluctuating intensity decreases, which also contributes for the enhancement of flow stability. Detailed observation of tip leakage flow structures illustrates that it is more effective to improve the flow stability by controlling the tip leakage flow released from near mid-chord.