Mechanics of a drop after striking a stagnant water layer

Abstract

This report represents a first step in the theoretical analysis of sheet flow with rainfall impinging on the free surface. This is a common occurrence in urban areas and many design procedures do not recognize the added resistance due to the rainfall. The analytical approach consists of the numerical solution of the Navier-Stokes equations, including surface tension as a boundary condition, using a Synthetic-Cell-Fluid scheme which rigorously conserves mass and momentum. The results include a maximum impact pressure model and a quantitative discussion of pressure distribution, boundary shear, the effect of surface tension, the free surface configuration, and the various forms of energy and its transformation during the impact process. Experiments were performed consisting of drop impact pressure measurements using various drop sizes, impact velocities and water layer depths. These data were used to successfully verify the theoretical work.