Large-eddy simulation of three-dimensional aerofoil tip-gap flow

Abstract

Tip-gap flow is inevitable between the rotor and endwall in rotating machinery, which can lead to operation instability, blockage effects, energy loss, and even cavitation in water. In this study, large eddy simulation of the tip-gap flow of a three-dimensional aerofoil in a linear cascade with a moving endwall are performed. A series of aerofoils are designed with different section parameters (chord, thickness and camber), pitch angles, and tip-gap sizes. Detailed analysis of mean flow field, turbulence statistics and tip-leakage vortex (TLV) centre trajectory is performed to determine the parameter effects. The section parameters with the main influence on TLV is found to be the gap width. Larger chords and thicknesses can effectively suppress the TLV, whereas the pitch angle has small influence. The gap size has a significant effect on the TLV evolution, and in particular, small gaps lead to completely opposite characteristics compared with large gaps by restraining the TLV close to the suction surface and endwall. Quantitative analysis of the TLV centre wandering phenomenon demonstrates the unsteady nature of TLV. Furthermore, a duct propeller is simulated with the rotor tip designed to suppress the TLV, which turns out to improve the whole hydrodynamic performance of duct propeller.