Effects of rotor blade tip clearance on total aerodynamic performance in a radial inflow turbine

Tip clearance flow in a radial inflow turbine rotor blade under stage environment was investigated by 3-dimensional viscous flow simulation. The results indicate that for tip uniform clearance less than 2 percent of the rotor blade exit height, a decrease of 1.5 percent in stage efficiency and a slight reduction of the flow rate occur for each percent increase in the rotor blade tip uniform clearance. There is a notable difference of the stage aerodynamic performance affected by radial clearance at the rotor exit and axial clearance at the rotor entrance, respectively. Radial clearance increases at the rotor exit have about 8.3 times the effect on stage efficiency decrease as axial clearance increases at the rotor entrance, while the flow rate enlarged by radial clearance increase is 4.2 times greater than that reduced by axial clearance increase. Moreover, the distinction is mainly at the top region of the rotor when the tip clearance flow field was compared with experimental results documented.