The Effects of Stepped Tip Gap on Performance and Flowfield of a Subsonic Axial-Flow Compressor Rotor

Abstract

This paper investigates the flow field at the tip region of compressor rotor. In particular, the effect of stepped tip gaps on the performance and flowfield of an axial-flow compressor rotor was reviewed using both experimental and computational methods. An axial compressor rotor with no inlet guide vanes was tested under subsonic condition. A parametric study of clearance levels and step profiles was performed using eight different casing geometries. This study was aimed at comparing compressor performance in specified configurations. The experimental results showed that the inclusion of stepped tip gaps with the small clearance level gave increased pressure ratio, efficiency, and stall margin throughout the mass flow range at both speeds. However, when using medium and large clearance level, the benefits of stepped tip gaps were not noticed for all rotor operating conditions if compared with the baseline case. Steady-state Navier-Stokes analyses were performed for cases involving small clearance level and stepped tip gap geometries. They highlighted the mechanisms associated with performance improvement. The numerical procedure correctly predicted the overall effects of stepped tip gaps. Detailed numerical simulation results showed that the interaction between the stepped groove flow and blade passage flow could entrain the blockage produced by upstream tip leakage flow into the tip gap of adjacent blades of the compressor rotor. It is through this process that stepped tip gaps can help dissipating blockage that was caused by upstream tip leakage flow. Thus the path and extent of the blockage in the tip region is altered to increase the passage throughflow area and so, the rotor performance can be improved.