Numerical study on dynamics of double droplets impacting simultaneously on porous media

The dynamic characteristics of double droplets impacting simultaneously on porous media are investigated using the level set method. The effects of horizontal distance between two droplets, droplet size, impact velocity, particle diameter, dynamic viscosity, and porosity on spreading, jet formation, and penetration are analyzed. Notably, phenomen on such as bubble entrainment, bubble bursting and scattered droplet formation, primary and secondary jet breakup have been observed. Bubble entrainment is more likely to occur when the two droplets are tangential to each other. The liquid jet is higher and more prone to breakup and form secondary droplet at larger droplet sizes, higher velocities, and smaller particle diameters and porosities. Extremely large or small spacing and viscosity are not conducive to the secondary droplet formation. An increase in distance, droplet size, and impact velocity can promote both spreading and permeation. Larger particle diameters and porosity facilitate droplet penetration but hinder droplet spreading on porous surfaces. As viscosity increases, the spreading factor and liquid jet height initially increase and then decrease, with a corresponding reduction in penetration depth and volume fraction of liquid embedded in the porous substrate. The stretching of the liquid jet affects volume fraction of the liquid embedded in the porous substrate.