Investigation of the Shear Flow Effect and Tip Clearance on a Low Speed Axial Flow Compressor Cascade

This paper explores the effect of inlet shear flow on the tip leakage flow in an axial flow compressor cascade. A flow with a high shear rate is generated in the test section of an open circuit cascade wind tunnel by using a combination of screens with a prescribed solidity. It is observed that a stable shear flow of shear rate 1.33 is possible and has a gradual decay rate until 15 times the height of the shear flow generator downstream. The computational results obtained agree well with the available experimental data on the baseline configuration. The detailed numerical analysis shows that the tip clearance improves the blade loading near the tip through the promotion of favorable incidence by the tip leakage flow. The tip clearance shifts the centre of pressure on the blade surface towards the tip. It, however, has no effect on the distribution of end wall loss and deviation angle along the span up to 60% from the hub. In the presence of a shear inflow, the end wall effects are considerable. On the other hand, with a shear inflow, the effects of tip leakage flow are observed to be partly suppressed. The shear flow reduces the tip leakage losses substantially in terms of kinetic energy associated with it. 1. Introduction In an axial flow compressor, the relative motion between the rotor and the casing necessitates some clearance between them. In the past, limitations of manufacturing technology to produce tight tolerances for the compressor rotor lead to the large tip gap. The undesired excessive tip gap may also develop over a long period of turbomachine operation due to wear and tear of parts. This functional requirement is associated with the undesired loss due to the interaction of the tip leakage flow with the mainstream, passage vortex, boundary layers of the blade, and the end wall near the tip regions. Therefore, the flow through the blade rows becomes three-dimensional and complex. A larger number of theoretical, numerical, and experimental studies exist on the tip leakage flow related to compressor aerodynamics. The formation of tip leakage vortex and its downstream advancement while interacting with the mainstream flow and the surface boundary layers becomes the flow features of the tip leakage flow. Rains [1] and Chen et al. [2] described the formation of the tip leakage vortex under the influence of the pressure gradient across the tip gap bound by the blade surfaces and its interaction with the mainstream. Storer and Cumpsty [3] studied the tip leakage flow in a compressor cascade by both experimental and numerical investigation and