The effect of tip clearance flow on compressor performance

Complex turbomachinery tip clearance flow field was investigated using a finite volume computational method which solves three-dimensional Reynoldsaveraged Navier-Stokes equations. Compressor vanes with NACA65-1810 blade section and tip clearances were tested. The formation of the leakage vortex flow caused by pressure gradient across blades and its interactions with blade passage secondary vortex flow were examined. The solutions were compared with known data. Very good agreements were achieved in predicting the flow structures in both the blade channel and the tip clearance region. It was found that the mechanism of the tip clearance effect on compressor performance is due to the interactions between the passage vortex of lower energy loss and the tip leakage vortex of higher energy loss. At certain tip clearance, the two vortices closely interact with each other and the overall vorticity strength is reduced. The total energy loss is thus a minimum and it can be considered as an optimum tip clearance.