Research On The Multiphase Coupling Problems Of Droplet Impact To Liquid Film And Solid Surface

The existing studies of multiphase f low of droplet impact are more limited to the vertical impact processes with the influence of gravity is usually neglected.However,in this work,single(double)two-dimensional droplet(droplets)is(are)initially placed above a liquid film or a solid surface and falls(fall)freely under gravity with a given horizontal velocity.To solve this problem,a hybrid method is chosen,in which the flow field is solved by us ing the lattice Boltzmann method and the interface is captured by solving the Cahn-Hilliard equation directly.At a fixed value of density ratio(ρ~*)or viscosity ratio(μ~*)of droplet to ambient fluid,the effects of Weber number(We),Bond number(Bo)and properties of impact substrate(dimensionless liquid film thickness H~*or the range of contact angleθ_R≤θ≤θ_A)on droplet impact are investigated.From the result of a single droplet impact onto liquid f ilm,it can be concluded that by increasing the We,a higher right jet can be generated,but it has an opposite influence on the left jet.A small Bo will also lead to a small splashing structure.And there exists a critical value of H~*,when the thickness is lower than it,the right jet height would increase with H~*,otherwise,it would decrease with H~*.By analyzing the phenomenon of a single droplet impact to solid surface with different properties,it can be found that the increasing of We can increase the maximum tensile length of droplet,but has little inf luence on the steady deformation structure.However,the bigger of Bo,the larger of steady spreading length will be,the left and right edge contact angles will become smaller correspondingly.And there exists a negative correlation between spreading rate of droplet andθ_A.Meanwhile,θ_R will increase the steady spreading length,but will decrease the steady left and right contact angles.Comparing the impact phenomenon of double droplets with that of single droplet,it is found that the double droplets successively impacting onto liquid film can lead to a claw structure on the right side,together with higher final splash structure and larger spreading length.When double droplets impact to solid surface one after the other,the length of steady spreading length will be increased,but makes no difference to left and right contact angles.Furthermore,it is suggested to choose the nodal discontinuous Galerkin-lattice Boltzmann method to solve much more droplet impact problems.