Influence of tip clearance heights on the flow field and performances of a supersonic expander

The three-dimensional Reynolds-averaged Navier-Stokes equations and the standard k-ε turbulent model were adopted to simulate numerically the flow field and performance of a supersonic expander with different tip clearance heights. The results show that tip clearance height significantly impact on the local flow characteristics in the three-dimensional flow passage and the overall performances of the supersonic expander. With the increasing of the tip clearance height, the highest relative Mach number of airflow decreases, and the scope of high speed reduces. The leakage vortex strengthens, scale largens, transverse and radial movement significantly, and the leakage loss increased, but the loss of shock waves and interaction of shock and boundary layer reduced. Expansion ratio of supersonic expander firstly increased and then decreased, and the isentropic adiabatic efficiency reduced gradually. The main source of loss in the three-dimensional flow passage of supersonic expander with clearance is the friction loss of low energy fluid near the suction surface and bottom wall and the leakage loss. The scope of clearance height should be selected between 0.9%h₀ and 1.5%h₀.