Drop inertia and its contribution to turbulent coalescence in convective clouds. Part I: drop fall in the flow with random horizontal velocity

The results of simulated drop fall in horizontal flows with the vertical shear of different kinds (constant linear, periodic, and with random velocity distribution) are presented. It is shown that the inertia of drops is significant enough to lead to substantial drop velocity deviations from the velocity of the flow and to the generation of relative velocity between drops of different sizes. For small droplets the velocity difference caused by turbulence is of the same order as the difference in terminal fall velocities. The results of calculations of drop fall through the horizontal flow with the random Kolmogorov spectrum distribution of velocity indicate that a comparable impact of turbulence in this flow is significant for the whole spectrum of drop sizes and that it even increases for small droplets. -Authors