Three-dimensional numerical investigation of drop collisions in a vacuum

The results of three-dimensional numerical simulations of drop collisions without the effect of a surrounding environment are presented. The numerical model is based on an Eulerian, finite-difference, Volume-of-Fluid method. Surface tension is included using the Continuum Surface Force method. Three types of collisional behavior are investigated: head-on, off-axis and collisions between a spherical translating drop and an excited drop.; Head-on collisions using equal size drops with three different fluid properties of water, mercury and tetradecane are presented. Various drop diameters ranging from 200 μm to 5 mm are considered. A separation criteria based upon deformation data is found. The lower critical Weber numbers are found for mercury and water drops. Tetradecane drops never result in separation for the range of Weber numbers considered. The effect of Reynolds number is investigated and regions of permanent coalescence and separation are plotted in the Weber-Reynolds number plane. The role of viscosity and its effect on dissipation is also investigated.; Off-axis collisions results are presented for equal size water drop with diameters ranging from 10 μm to 2 mm. The upper critical Weber number are found for six different diameters and is observed to approach a value of 18 as the diameter is increased. A deformation based separation criteria is observed to vary linearly as a function of both Weber and impact number. Plots of collisional outcomes in the Weber-Reynolds number plane are provided for grazing collisions and collision with an impact number of 0.9. The critical Reynolds number approaches zero for grazing collisions, while a decrease in impact number shifts the critical Reynolds number to 100.; Lastly, the results from collisions between a spherical water drop and an excited water drop are presented. An excited drop is generated by colliding two initially spherical drops. Only head-on collisions with respect to the single spherical drop are considered. The results indicate that the presence of an internal flow in the excited drop causes a stabilizing effect on the overall collision for the range of Weber numbers considered.