Experimental Investigation of the Flow Mechanisms and the Performance Change of a Highly Loaded Axial Compressor Stage with/without Stator Hub Clearance

Baojie Liu,Ying Qiu,Guangfeng An,Xianjun Yu

doi:10.3390/app9235134

Abstract

Three-dimensional corner separation is common in axial compressors, which can lead to large flow loss and blockage especially when it evolves into the corner stall (open separation). In this paper, the evolution of the three-dimensional flow structures inside a cantilevered stator of a 1.5 stage low-speed highly loaded axial compressor as the stator hub clearance varies, and its effect on the whole compressor performance are investigated experimentally. Firstly, when the stator hub is sealed, the hub corner stall will occur at small mass flow rate conditions. Then, when a very small stator hub clearance is introduced, the leakage flow tends to strengthen the hub corner separation at large mass flow rate conditions and prompts the occurrence of hub corner stall as the mass flow rate decreases. This is mainly caused by the fact that the leakage flow has relatively low energy due to the viscosity effect in the clearance and large flow loss generation as the clearance flow comes across and mixes with the transverse secondary flow. Finally, when the stator hub clearance increases, the effect of the flow viscosity becomes very weak and could be ignored, so the enhanced leakage flow can suppress the transverse migration of the low energy flow near the hub, and the hub corner separation at large mass flow rate conditions could be weakened and the hub corner stall at small mass flow rate conditions could be removed or delayed. As the stator hub clearance varies, the flow structures inside the stator passage could be summarized into five typical flow structures, and this is closely associated with the performance of the compressor.

Highlights

Three-dimensional corner separation is an inherent flow feature in axial compressors, the induced flow blockage and loss of which can deteriorate the compressor performance
When the corner separation turns into a corner stall, large backflow will occur at the corner surrounded by the blade suction surface and the end wall [1,2], and the compressor performance will decrease rapidly [3,4]
Of the results on the suction sidealmost and thedid hubnot arechange shown with here. the Compared with the at zero thescale hub corner separation, the situation is different as the stator hubintroduction clearance varies

Summary

Introduction

Three-dimensional corner separation is an inherent flow feature in axial compressors, the induced flow blockage and loss of which can deteriorate the compressor performance. Sci. 2019, 9, 5134 secondary flow in the wall boundary layer, it can suppress the migration of the low energy flow to accumulate in the corner surrounded by the blade suction surface and the end wall and the corner separation is weakened . This conclusion was verified by Lakshminarayana and Horlock [16,17,18], who conducted some experiments in the linear cascade and put forward that there exists an optimum clearance size that makes the flow loss to be the minimum

Results

Discussion

Conclusion