Abstract: In order to reduce the serious tip leakage loss caused by low aspect ratio blade in radial turbine for compressed air energy storage (CAES) system, NACA0004 airfoil is adopted to form the thickness distribution near blade tip to improve the aerodynamic performance. Three-dimensional flow structure for the blade with NACA0004 airfoil tip is investigated numerically by using ANSYS CFX software. The effects of NACA0004 airfoil tip on the structure and loss characteristics of tip leakage flow are analyzed when tip clearance increased from 0.5% to 8%. The results show that the effect of blade with NACA0004 airfoil tip on isentropic efficiency of radial turbine varies with tip clearance. The isentropic efficiency of radial turbine is reduced by 0.3% when tip clearance is 0.5%, while the isentropic efficiency can be increased from 0.4% to 1.9% when tip clearance is varied from 1% to 8%. The tip leakage loss mechanism of the blade with NACA0004 airfoil tip is varied with the increase of tip clearance. When tip clearance is 0.5%, the leakage flow is concentrated near blade suction surface, and more leakage flow, which also increases the flow loss, is found near outlet region of rotor. However, when tip clearance is increased from 1% to 8%, the pressure difference between the blade pressure surface and suction surface near the leading edge and trailing edge of the blade is reduced, the leakage velocity and the mixing strength with the mainstream is decreased, and the flow loss is thus suppressed. When NACA0004 airfoil tip is adopted, the power output of the radial turbine has not been reduced, and the maximum deformation and equivalent stress of blade meet the requirements of structural size and material strength. The above research can provide a reference for reducing tip leakage loss of radial turbines with similar structure.

Key words: compressed air energy storage, radial inflow turbine, tip clearance flow, blade profile, NACA0004 airfoil