A stochastic droplet collision model with consideration of impact efficiency

Abstract

A stochastic droplet collision model (Sommerfeld [9]), based on the creation of a fictitious collision partner is described, taking into account impact efficiencies. The model of O’Rourke [5] is considered to predict the outcome of water -droplet collisions, being grazing or coalescing, and to predict post-collision velocities. The relevance of impact efficiencies is discussed for water droplet collisions on the basis of the inertial parameter. As a result, regions of importance are defined, in which the impact efficiency has to be taken into account. The influence of impact efficiency on coalescence rates of water droplets is discussed by comparing normalised critical displacements and collision frequencies. The assumption of a step function for modelling impact efficiencies, as valid for laminar flows, is not applicable to turbulent flows if the integral scale of turbulence is in the order of the large droplet diameter.