EFFECTS OF FLOW NONUNIFORMITY AND RELATIVE ACCELERATION ON DROPLET DYNAMICS

A computational study on the dynamics of single droplets is performed in two gas flows at moderately high Reynolds numbers. One is Poiseuill e flow in which the gas is either nitrogen or helium and the other is a counterflow formed by two opposed streams of nitrogen. The focus of the study is to review the methodologies used for representing the eff ects of flow nonuniformity and relative acceleration on droplet motion at moderately high Reynolds numbers. The motion of the droplets is ob served to be affected by flow nonuniformity and unsteadiness, characte rized respectively by dimensionless parameters kappa and A(C), and the effects due to nonuniformity and rate of change of relative velocity are separable. It is determined that acceleration and deceleration aff ect the drag and lift on droplets in dissimilar ways. The lift force c aused by flow nonuniformity is in the same direction as kappa in Poise uille flow, whereas it is in the opposite direction as kappa in counte rflow. It is noted that the radius of curvature of droplet trajectory affects lift force more strongly than drag force. Modified correlation s for the drag and lift coefficients as functions of the Reynolds numb er and dimensionless parameters characterizing the flow nonuniformity and unsteadiness are proposed.