Early-stage deformation of liquid drop in shock induced high-speed flow

In the present study the early-stage deformation of a liquid drop in the high-speed flow induced by a planar shock wave was experimentally investigated using the shock tube facility and high-speed photography technique. It was found that the variation of the flow and drop conditions may cause significant divergences in the morphology of the drop deformation, even though such classical dominant parameters such as the Weber number or the Reynolds number are conserved. The divergences are mainly on the lee side of the drop, involving major characteristics of the circular ridges, the wrinkle band and the concave-plane convex profile of the lee side polar zone. Numerical simulations of the flow around a sphere show evident correspondence between the deformation patterns and the flow structures as well as the aerodynamic forces distributed along the sphere surface. For further evaluation and understanding of the detailed deformation features, a set of equations were deduced from hydrodynamic theories with necessary simplification. Feeding the equations with the aerodynamic data from numerical simulations, the calculation results indicate that, the main mechanism behind the deformation on the lee side of the drop is the squeezing effect of the uneven pressure distribution, rather than the accumulation effect of the surfacial flow induced by friction, with the former about two orders higher than the latter. Moreover, the drop profiles calculated following the pressure acting theory were found to agree quite well with the real drop patterns, not only in the deformation characteristics but also in the order of deformation magnitudes.