A NUMERICAL STUDY OF THE RAINDROP IMPACT PHENOMENA

CHI-HUA HUANG, Purdue University

Abstract

An understanding of the mechanics involved in the raindrop impact phenomenon is essential in order to define a resistance parameter against the erosive force. Numerical techniques were used to study the raindrop impact phenomenon. Two separate but interrelated studies were performed to examine this complex process. First, the fluid dynamics of a raindrop after it encountered a solid surface was simulated. In the second numerical experiment, the behavior of an elastic solid material under simulated raindrop impact loading was studied. The Marker and Cell (MAC) numerical technique was used to examine the fluid dynamic part of the raindrop impact phenomenon. The impact of a spherical drop on a rigid surface was simulated. Results indicated that the impact pressure were neither uniform nor constant. Extremely high values occurred at the very instant of impact and diminished to about five times the steady state stagnation pressure after 5 (mu)seconds. The maximum pressure was at the contact circumference. The jetting velocity at the rigid surface was twice the impact velocity. The simulated raindrop impact load was applied to a elastic medium in order to show the surface deformation pattern. The mechanical properties were selected to resemble a soil material. The solid dynamics equation with the assumption of linear elasticity were solved by a finite difference scheme. Under simulated impact loading, the surface deformation was more uniform for materials with high compressive strength. For low strength materials, a hemispherical shaped depression formed. This greatly reflects the characteristics of the transient, non-uniform impact load. These results led us to the conjecture of important criteria in defining the soil resistance against raindrop impact. These criteria are: the soil deformation characteristics, the soil shearing strength, and the surface micro-relief.

Degree

Ph.D.

Subject Area

Agronomy

COinS