Analysis of tip-gap size on tip-leakage flow in an axial fan at design and off-design operating conditions

Abstract

Large-eddy simulations of the flow in a ducted axial fan are performed to investigate the dynamics of tip clearance flow for several tip-gap sizes at design and off-design operating conditions. The Navier-Stokes equations are solved on a multi-block structured 140-million-cell mesh in a rotating frame of reference for a single out of five blades with periodic boundary conditions in the circumferential direction and prescribed inflow conditions based on experimental data. The results show that increasing the tip-gap size results in various vortices in the tip-gap region, i.e., tip-leakage, separation, and induced vortices, which enlarge the diameter and the strength of the main tip vortex. For the off-design operating condition, the tip-gap vortex for the smallest tip-gap size decays faster than that for the design operating condition. For the largest tip clearance, spiral vortex breakdown occurs at the design operating condition.