The influence of surface roughness on cloud cavitation flow around hydrofoils

摘要

The aim of this study is to investigate experi-mentally the effect of surface roughness on cloud cavitation around Clark-Y hydrofoils. High-speed video and particle image velocimetry(PIV)were used to obtain cavitation pat-terns images(Prog.Aerosp.Sci.37:551–581,2001),as well as velocity and vorticity fields. Results are presented for cloud cavitating conditions around a Clark-Y hydrofoil fixed at angle of attack of α=8?for moderate Reynolds number of Re = 5.6×105.The results show that roughness had a great influence on the pattern,velocity and vorticity distribu-tion of cloud cavitation.For cavitating flow around a smooth hydrofoil (A) and a rough hydrofoil (B), cloud cavitation occurred in the form of finger-like cavities and attached subulate cavities, respectively. The period of cloud cavita-tion around hydrofoil A was shorter than for hydrofoil B. Surface roughness had a great influence on the process of cloud cavitation.The development of cloud cavitation around hydrofoil A consisted of two stages: (1) Attached cavities developed along the surface to the trailing edge;(2)A reen-trant jet developed, resulting in shedding and collapse of cluster bubbles or vortex structure. Meanwhile, its devel-opment for hydrofoil B included three stages:(1)Attached cavities developed along the surface to the trailing edge,with accumulation and rotation of bubbles at the trailing edge of the hydrofoil affecting the flow field;(2)Development of a reentrant jet resulted in the first shedding of cavities.Inter-action and movement of flows from the pressure side and suction side brought liquid water from the pressure side to the suction side of the hydrofoil,finally forming a reentrant jet.The jet kept moving along the surface to the leading edge of the hydrofoil,resulting in large-scale shedding of cloud bubbles.Several vortices appeared and dissipated during the process;(3)Cavities grew and shed again.