Abstract: The generation and movement of the bubble inside a droplet affect the movement of the droplet intensively when the droplet impacting on a wall. The generation and movement mechanism of the bubble inside an impacting droplet are researched by the coupled solution of the coactions of gas-liquid two-phase flows with wall, based on the combined Level Set-VOF method for gas-liquid interface tracking and the wall wetting model. The results show that the pressure between the droplet and wall far bigger than the pressure inside the droplet and the different velocity distribution of the liquid and gas beside the contact line are the primary causes of the bubble generation and movement when droplet impacting on a wall. The liquid layer width experiences an increase process first and then decrease, and finally forms a bubble. The final bubble diameter increases linearity with the impacting velocity and is affected intensively by the velocity when the impacting velocity is smaller than certain value. The maximum liquid layer width increases linearity with the impacting velocity, while the impacting velocity affects the final bubble diameter weakly when the impacting velocity is bigger than certain value.

Key words: droplet;impacting;wall;bubble;movement