Numerical simulation of wall impinging drops

Shiladitya Mukherjee, Purdue University

Abstract

In this work, numerical investigations of impinging drops on dry and wet walls are reported. A multiple-relaxation-time (MRT) axisymmetric multiphase lattice-Boltzmann (LB) model is employed along with a model for simulating surface wettability. For simulations on wet walls, a recently developed high density-ratio LB model is employed. This model is extended in this work to include the MRT collision model and thereby achieve Reynolds number which are 50% higher, and adapted to an axisymmetric coordinate system. The model is evaluated by verifying the Laplace-Young relation for a liquid drop and comparing the computed frequency of oscillations of an initially ellipsoidal drop with analytical values. Agreement within 8% is obtained. When the impingement is on dry walls, the outcomes are deposition, rebound and splash. In deposition, the dynamic contact angle evolution during spread and recoil was shown to be influenced by the drop inertia and transient effects of the varying contact line speed. The tendency to rebound increases with increase in static advancing and receding contact angles, and the shape of the drop at the time of rebound becomes elongated as Weber number (We) and equilibrium contact angle increase. The transition to splash depends on We and Oh. Splash at low We and high Oh leads to formation of a liquid crown before it breaks up into smaller droplets. When the impingement is on wet walls, the growth of the liquid crown and its breakup are influenced by the wall liquid film thickness and the ambient gas density and viscosity. When the wall-film thickness is small, the growth rates of the crown radius and height increase with increasing thickness and breakup time is increased. On thicker films, however, the growth rates have the opposite trend. The crown breakup time is further increased. When the gas density increases, the growth rates of crown radius and height decrease, and crown breakup occurs at a longer time. Increasing the gas viscosity has a weak influence on the growth rate of crown radius. However, at higher gas viscosity the crown height grows faster and breaks up earlier.

Degree

Ph.D.

Advisors

Abraham, Purdue University.

Subject Area

Mechanical engineering

COinS