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Mechanism of stability enhancement with shallow reversed slot-type casing treatment in a transonic compressor
Author(s): Zhidong Chi, W. L. Chu, Haoguang Zhang
Keywords: Axial compressor; Casing treatment; Numerical simulation; Tip leakage flow; Stall margin
This article presents detailed numerical analysis of a novel slot-type casing treatment in a transonic axial compressor stage at different rotating speeds. The research compressor rotor is tip-typical so it is suitable for casing treatment (CT) to improve flow stability and enhance compressor stall margin. Due to the geometric limitation, a novel shallow reversed slot-type casing treatment (SRSCT) is designed and analyzed to clarify the mechanism of stability enhancement of casing treatment. The numerical results show that the instability characteristics under smooth casing are obviously different at two rotating speeds, which inevitably leads to the difference of the effect of SRSCT on the stability enhancement. It shows that the blockage induced by suction surface separation dominates at 100% design speed, while the blockage induced by tip leakage flow dominates at 80% design speed. Based on the different instability mechanism, this paper focus on the effect of casing treatment and the internal flow field difference caused by casing treatment. Firstly, the difference at two rotating speeds indicates that casing treatment is more efficient for tip blockage stall, manipulation of leakage flow by casing treatment is the principal reason for stability enhancement. Because of the the pressure difference, tip leakage flow is sucked into rear slot cavity and re-injected into the tip region at front slot cavity. Secondly, the pressure field and passage shock distribution are analyzed at different speeds, it shows that more effective circulation of casing treatment affected by static pressure field and passage shock wave at 80% design speed presents better stability enhancement effect. Furthermore, this paper pays attention to the instability characteristics under the effect of casing treatment. It shows when the mass flow approaching to stability boundary, the stator passage blockage may be dominant for triggering the compressor stage into unstable flow condition.

Journal of Applied Fluid Mechanics

The Journal of Applied Fluid Mechanics (JAFM) is an international, peer-reviewed journal which covers a wide range of theoretical, numerical and experimental aspects in fluid mechanics. The emphasis is on the applications in different engineering fields rather than on pure mathematical or physical aspects in fluid mechanics. Although many high quality journals pertaining to different aspects of fluid mechanics presently exist, research in the field is rapidly escalating.