Abstract
In this paper, a novel tip clearance control structure, the tip control hole (TCH), is proposed, which is appropriate for the radial turbines with the characteristics of low manufacturing cost, thin blade, insufficient tip space and insufficient strength of winglets. Under the original conditions, when the tip clearance height is 2% of the outlet blade height, the effect from the position and number of holes on the overall turbine performance is discussed, and the physical mechanism of efficiency improvement is analyzed. It is found that the optimal scheme of single hole and multiple-hole structures increase the total-total efficiency by 0.173% and 0.198%, with the relevant the tip leakage decreased by 0.812% and 1.058%. The results show that the closer the holes are to the upstream of the impeller, the better the optimization effect is compared with the original turbine. The main optimization mechanism of leakage control is to restrain the tip leakage vortex. The control hole decreased the scale of the vortex, makes the position of the vortex close to the suction surface. In the optimal scheme, the tip control hole reduced the pressure difference between the suction surface and the pressure surface, suppressed the leakage, and plays an auxiliary role in improving the efficiency.
