Dynamics of Oscillating Drops with Thermocapillary Effects

Abstract

The dynamics of oscillating drops warming up in a hot gas environment is investigated via numerical simulation. The formation of surface and internal flows, due to variation of surface tension with temperature, and their impact on the oscillations are discussed. Both surface and ambient temperature disturbances are considered in terms of spherical harmonics. The effects of various parameters including modes of surface and temperature disturbances on period and amplitude of oscillations, kinetic and surface energies, and temperature field are studied. The most obvious feature of thermocapillary flows is demonstrated by vortices whose number and strength varies with the mode of temperature disturbance. These vortices tend to modify the amplitude of oscillations and enhance the kinetic energy. It is also shown that the decrease of the surface tension with increasing temperatures results in the increase of the period of oscillations while decreasing the surface energy. Due to the presence of thermocapillary flows, at long times, the equilibrium shape of the drop is not spherical and the kinetic energy approaches nonzero asymptotic values. The average temperature shows a nearly linear increase in time while the root mean square temperature, used to indicate the spatial variation, levels off after a fast initial growth.