Analysis of hydrodynamic and loss characteristics of hydrofoil under the effect of tip clearance

Tip leakage flow widely exists in fluid machinery, which affects the unit's mainstream flow state and induces significant flow loss. This study explores the relationship between vortex motion and hydraulic loss in the fluid field of single hydrofoil and tandem double hydrofoils under the effect of tip clearance. The validation work indicates that the simulation results in this study align with previous experimental findings, verifying the accuracy of the method employed herein. Further analysis reveals that: (1) The existence of clearance can induce a series of vortex structures such as tip leakage vortex(TLV), tip separation vortex(TSV), hairpin vortex(HV), and wingtip vortex(WTV). The length of TLV is greatly affected by increase of clearance width. The TLV and TSV undergo three stages of generation, development, and dissipation during the fluid flows though hydrofoil, greatly affecting flow stability. (2) Vortex motion is accompanied by significant turbulent pulsation, resulting in entropy production and inducing hydraulic loss. The calculation results indicate that approximately 75% of the loss is generated in the zones of midstream and downstream(V₂+V₃), where the vortex structure is full developed and the vortex motion is violent. Additionally, the loss caused by turbulent dissipation term accounts for 98%, while the loss caused by viscous dissipation accounts less 2%. (3) The loss in single hydrofoil is approximately positively correlated with the clearance width, while it fluctuates with the increase of width in tandem double hydrofoils.