Surface tension effects on the behavior of two cavities near a rigid wall.

Surface tension effects on the behavior of two initially spherical cavities growing and collapsing axisymmetrically above and near a rigid wall are investigated numerically by boundary integral method. The numerical simulations are performed for different dimensionless maximal cavity sizes, different dimensionless distances between the two cavities and those between the wall and the two cavities, and different values of Weber number. It is found that surface tension effects will resist the deformation of a cavity and make it closer to spherical during its growth phase, and make it collapse faster. For the case where the lower cavity is much smaller than the upper one, when the Weber number is less than or equal to 20, during the collapse phase, surface tension will have substantial effects on the behavior of the lower cavity such as change the form or the direction of its liquid jet if the Bjerknes forces to the lower cavity induced by the wall and the upper one are nearly equal. In all of the other cases, when the Weber number is greater than or equal to 10, surface tension will not have qualitative effects on the behavior of the cavity but change the length, width or sizes of its liquid jet. It is also found that for a convex cavity, surface tension has the effects on cavity behavior similar to those of the difference between the ambient pressure and the saturated vapor pressure inside the cavities. The above phenomena induced by surface tension effects are explained by this mechanism.