Research On Collapse Characteristic Of A Cavitation Bubble Attached To The Solid Wall Near The Free Surface

If the local pressure fall to saturation vapor pressure in the flow field, the phase of the surrounding liquid convert from liquid into gas, and cavity occurs. Cavitation phenomenon, which exists widely in hydraulic machinery, high speed water tunnel, underwater weapon, hydrofoil, pumps and propeller and so on, is an important factor that restricts the development of hydraulic machinery and underwater weapon. Especially, high-speed jet and pressure shock from the collapse of cavitation bubble will damage the solid wall. Currently, the literature about cavitation bubble attached to the wall collapsing near the free surface is less, and differs from emphasis point. The research on cavitation bubble attached to the solid wall was conducted by numerical simulation. The collapse characteristic of the cavitation bubble was also analyzed by Fluent.This paper uses volume of fluid (VOF) model and unsteady method to solve Navier-Stokes equation. Firstly, when the cavitation bubble attached to the horizontal wall collapsed under different level of free surface, collapse pressure and velocity field distribution was studied. Secondly, collapse characteristics of the bubble adhered to the vertical wall in different angles and different heights of free surface was studied by numerical analysis. Finally, the influence of surface tension on collapse time, collapse pressure and rebound phenomenon was discussed.The results show that it is feasible to use the VOF model in Fluent to simulate the collapse phenomenon of cavitation bubble near the free surface. In the case of collapse process of cavitation bubble on the horizontal wall, with the decrease of distance between free surface and solid wall, collapse time is shortened and the strength of the jet increases. After the collapse mode of cavitation bubble changed, the wall pressure decreases, and velocity field distribution changes. In the case of collapse process of cavitation bubble on the vertical wall, with the decrease of height and angle, collapse time shows a decreasing trend and rebound phenomenon appears and impacts on the velocity and direction of the jet. Taking into account the surface tension, the time of collapse shortens, and collapse point changes, collapse pressure shock becomes larger, jet on free surface arises ahead.