液滴撞击覆有液膜平面的撞击力特性数值模拟研究

Numerical simulation for impact force characteristics of droplet impacting on plane covered with liquid film

液滴撞击物体表面产生的撞击力对很多自然过程与生产活动都有重要作用。该文采用有限体积法及VOF(volume of fluid)方法数值模拟了液滴撞击覆有液膜的平面的撞击过程,研究了液膜厚度对撞击力的影响。数值计算得到了液滴撞击覆有液膜平面的撞击力瞬时值的变化规律、壁面上的压强分布及其演化规律。研究结果表明:液滴撞击覆有液膜的平面时,覆盖在壁面上的液膜能延缓壁面所受撞击力的上升速率,起到缓冲作用,且其缓冲作用随液膜厚度的增大而增大。随着液膜厚度由零开始增加,壁面所受瞬时撞击力峰值先随液膜厚度增大而增大;瞬时撞击力峰值达到最大后,继续增大液膜厚度,瞬时撞击力峰值随液膜厚度增加而减小,因此,液滴撞击覆有一定厚度薄液膜的平面达到的瞬时撞击力峰值最大。虽然液滴撞击无液膜覆盖平面达到的瞬时撞击力峰值不是最大,但是液滴撞击无液膜覆盖平面时,壁面上的压强远大于液滴撞击覆有液膜的壁面上的压强,且两者的演化规律不同。根据数值计算结果进行了无量纲分析,当液膜厚度小于液滴直径时,得到了液滴撞击覆有液膜平面的无量纲撞击力随无量纲时间的变化曲线。

The impact force generated by a droplet impacting on the surface of an object has important effects on many natural processes and production activities.In this paper,the finite volume method and the volume of fluid method are used to numerically simulate the impact process of a liquid droplet on a plane covered with a liquid film,and the influence of the liquid film thickness on the impact force is studied.Numerical calculations show the variation law of the instantaneous value of the impact force of the droplet impacting on the plane covered by liquid film,and the pressure distribution on the wall and its evolution law.The research results demonstrate that when a liquid droplet impacts on the plane covered with the liquid film,the liquid film can delay the rising rate of the impact force on the wall and play a buffering effect.The buffering effect increases as the thickness of the liquid film increases.With the increase of the thickness of the liquid film from zero,the peak value of the instantaneous impact force on the wall first increases,and then decreases after the peak value.Therefore,when a droplet impacts on the plane covered by a thin liquid film with a certain thickness,the peak value of the instantaneous impact force reaches the maximum.Although the peak value of the instantaneous impact force is not the largest as a droplet impacts on the dry surface,the pressure on the wall is much greater than that appears when a droplet impacts on the surface covered by a liquid film.The evolutions of the pressure on the wall are different between the two cases,the droplet impacts on the dry surface and the surface covered by a liquid film.According to the numerical results,the dimensionless analysis is carried out.For the case that the thickness of the liquid film is less than the diameter of the droplet,the variation of dimensionless impact force with dimensionless time is obtained.