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

Mahesh Varpe,A M Pradeep

doi:10.1155/2013/490543

Abstract

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.

Highlights

In an axial flow compressor, the relative motion between the rotor and the casing necessitates some clearance between them
Storer and Cumpsty [3] studied the tip leakage flow in a compressor cascade by both experimental and numerical investigation and found that the tip leakage vortex formed at the maximum loading point and moved downstream as the tip gap increased
The present study focuses on tip gaps of 0.5%, 1%, 2%, and 4% of the span that correspond to 0.65% C, 8 1.3% C, 2.61% C, and 5.22% C

Summary

Introduction

In an axial flow compressor, the relative motion between the rotor and the casing necessitates some clearance between them. The undesired excessive tip gap may 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. Khalid et al [4] studied the effect of tip clearance on end wall blockage in an axial compressor using a simple model similar to the definition of boundary layer displacement thickness. The end wall effect becomes more influential than the tip leakage flow in the loss mechanism. The tip leakage vortex exerts little influence on the development

Methods

Results

Conclusion