An analysis of the Circumferential Grooves Casing Treatment for transonic compressor flow

Abstract

The stall mechanism of the NASA Rotor 37 is investigated through the analysis of the critical flow structures near the stall under the transonic condition. The performance of the rotor with Circumferential Grooves Casing Treatment (CGCT) is also studied based on the Reynolds-Averaging Navier-Stokes approach. The study finds that stall margin improvement can be achieved without significant penalty on the efficiency for the two CGCT configurations applied. The effects of circumferential grooves on the critical flow structures are studied through the analysis of the tip leakage mass and momentum transport that further reveal the CGCT mechanism. transonic compressor, Circumferential Grooves Casing Treatment, stall margin, leakage mass and momentum transportation analysisCasing treatment as a passive flow control method to extend the stable operating range for a tip critical rotor has been used for years. While it can give rise to improved stall margin, there is usually an associated efficiency penalty. This is due to the lack of good knowledge on the mechanism of casing treatment, and the design often largely depends on ad hoc experience. Circumferential Grooves Casing Treatment (CGCT) is simple and effective in stall margin improvement. Much research has been done in this area. Rabe & Hah [1] studied the effects of the CGCT on the flow field of a transonic compressor both experimentally and computationally. Those effects include the change of incidence of the main flow near the blade pressure side, tangential velocity effect, segmentation of blade tip leakage vortex (BTLV) and the in-and outflow effects. Wilke and Kau [2] conducted a numerical study on CGCT on a HPC front stage. The circumferential grooves were reported to suppress the extension of the BTLV and improve the stall margin. Shabbir & Adamcyzk [3] studied the physical mechanism of the CGCT with an analysis on the axial momentum budget for a low speed rotor. Müller et al. [4] studied the effects of CGCT on an axial single stage transonic compressor both experimentally and numerically with four configurations of CGCT. The configuration with deep grooves and large coverage showed the best results on the stall margin improvement in both design and off design speed.However, the mechanism of CGCT is still not fully understood. This paper mainly focuses on the effects of CGCT on some critical flow structures related to the stall process. The leakage mass and momentum transport are analyzed for a better understanding of the mechanisms of CGCT. Although the stall is a highly unsteady process, the steady RANS method captures the stall related critical flow structures well. Thus the RANS method is believed suitable for a relative study on the casing treatment.This paper first discusses the critical flow structures at the near stall condition of smooth wall (SW) configuration. Then the rotor performance with CGCT is presented and compared with SW case results. CGCT effects on the critical flow structures are discussed to explain the per-

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