The more the bubble close to the freesurface, the narrower the bottom jet develops crosswise, and the larger the pressure gradient, the rising velocity and the height of the bottom jet is upwards.
After reflection, the average particle velocity near freesurface is equal to twice the piston velocity approximately, which agrees with macroscopic phenomena.
激波在自由面反射后，自由表面附近的粒子速度为活塞速度的二倍，这和宏观力学结果相同。
3
Considering the influence of the air on the velocity of flow, Volume of Fluids (VOF) method is used to track the freesurface.