Effect of tip clearance leakage on performance of centimetre-level high subsonic micro axial flow turbine

The effect of the tip leakage on the flow field structure and turbine performance of a 78.4mm diameter centimetre-level high subsonic micro axial flow turbine of a micro turbine engine(MTE) prototype was analyzed by numerical simulation. Results show that the relative tip clearance size of micro axial turbine is within the range of 3.1%-4.6%, which is higher than that of conventional axial flow turbine. The effect of tip leakage vortex extends towards the mid of the vanes, of which the leakage losses account for 35% of total losses of the turbine stage, showing a significant increase compared to the conventional axial flow turbine. Studies on the impacts of the law of the gap size of the centimetre-level high subsonic micro axial flow turbine have shown that, once the gap size for each increases by 1% of the blade height, the efficiency will decrease up to 1.9%, which is more distinct than the conventional turbine. Finally, an optimum gap size (0.4mm) was determined due to the restrictions of engineering installation (centrifugal deformation, thermal deformation, bearing clearance, machining and assembly errors, etc), and the performance parameter of the impeller was acquired by numerical simulation: total pressure ratio of 2.12, efficiency of 0.87, mass flow of 0.35kg/s.