The fact that the location of single circumferential casing groove can have a large impact on the stall margin of axial compressors has been actively investigated in recent years. However, it remains a tough challenge to numerically predict the groove performance and clarify its underlying mechanism on the difference of stall margin improvement (SMI) for different groove locations. In this paper, a single rotor, which had been proven to be a tip sensitive rotor with spike type stall inception, is tested and numerically simulated with an unsteady Reynolds averaged Navier-Stokes (URANS) solver. The test results show that the rear grooves perform better than the front grooves in this rotor. A multi-passage numerical scheme is used to capture the prestall process involving the unsteady cross-passage flow interaction. Although the calculation did not fully capture the measured trend of stall margin improvement, the numerical result did show that the front groove, which is the closest to the leading edge, generates the worst stall margin extension, and the rear groove, which is located right behind the front groove, gives the best stall margin improvement.
The prestall dynamics for smooth casing and the two typical grooves are chosen for a comparative study to clarify the underlying mechanism. Three different prestall processes are found. For smooth casing, a rotating disturbance evolves into spike after the interface between tip leakage flow (TLF) and incoming main flow (MF) spills in front of the leading edge. For the front groove, the interface is prevented by the groove to move forward during the throttling process. A modal wave is captured before stall. When the rear groove is applied, the interface location as a function of flow coefficient behaves much similar to the case of smooth casing. However, there is no any rotating disturbance, neither the modes nor the spike, with this groove. The flow is symmetric until all the passages break down at the same time.