Numerical and experimental investigation of stepped tip gap effects on a subsonic axial-flow compressor rotor

This article investigates the flow field at the tip region of compressor rotor. In particular, the effect of stepped tip gaps on the performance and flow field of axial compressor was reviewed using experimental and computational methods. An axial compressor rotor with no inlet guide vanes was tested under subsonic conditions. 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 levels, the benefits of stepped tip gaps were not noticed for all rotor operating conditions when 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 the 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 in dissipating blockage that was caused by upstream tip leakage flow. Thus, the path and extent of the blockage in the tip region are altered to increase the passage through-flow area, and so, the rotor performance can be improved.