Numerical study of shear stripping of a liquid drop under shock wave loading

The breakup pattern of a water drop in a high-speed air flow was numerically investigated under conditions which are typical for the stripping-type drop disintegration. Three-dimensional numerical simulations have been performed to investigate the complex interaction of a supersonic shock wave (Ma = 1.47) with a cylindrical water drop using the unsteady Reynolds-averaged Navier-Stokes approach. The Kelvin-Helmholtz Rayleigh-Taylor breakup model is employed to characterize the disintegration of the liquid drop process and a coupled level set/volume of fluids technique is applied to examine the topological changes of the gas/liquid interface. The computational approach has been validated by comparing the predicted displacement/-drift with time, acceleration with time, and drag coefficient of the drop against the experimental data. Comparisons, with good agreement, have also been made between the predicted drop length/width/area and the experimentally measured values to elucidate changes in the shape and size of the drop. Comprehensive flow visualization has been used to show the shock-liquid drop interaction process, i.e., the onset of drop compression/flattening, formation of vortices, production/distribution of vorticity, pressure distribution, inception of the downstream separation points and stripping points at the equator followed by their subsequent fusion. These detected qualitative features are consistent with the past experimental observations of stripping. It is demonstrated for the first time that turbulence is generated at the early phase of the shock cylindrical drop interaction process, with the maximum turbulence intensity reaching about 22 % around the recirculation zones and the wake region. In addition, the present study shows that the Kelvin-Helmholtz instability plays a more important role than the Rayleigh-Taylor instability in the process succeeding the shock impact on the drop.