Novel bionic wave-shaped tip clearance toward improving hydrofoil energy performance and suppressing tip leakage vortex

Abstract

The tip leakage vortex (TLV) is inevitable in hydraulic machinery with tip clearance, which leads to a decrease in runner efficiency and an increase in pressure fluctuation. In this paper, a novel method of bionic wave-shaped tip clearance was designed to improve the energy performance and suppress the TLV. The results show that the fluctuating entropy production was changed by the novel wave-shaped tip clearance. When the period number of the novel wave-shaped tip clearance is 1, the TLV scale decreases. The total entropy production decreases. The maximum increases in the lift and lift-drag ratio are 1.08 % and 5.11 %, respectively, under inlet velocity 5 m/s condition. When the period of the novel wave-shaped tip clearance increases to 4, the large-scale TLV is decomposed into several smaller vortex. The upstream vortex structure interacted with the downstream vortex and was intercepted for further development. The TLV core pressure increased. However, the entropy production rate increased, the lift and lift-drag ratio decreased. Analysis of novel wave-shaped tip clearance with different sizes was also carried out. When the amplitude of the novel wave-shape is equal to the tip clearance size, the inhibition effect on TLV is optimal and the performance improvement is the greatest.