Numerical study of hole formation in a thin flapping liquid sheet sheared by a fast gas stream

This study reports aerodynamics effects of a fully developed double-shear layer gas flow in the perforation and disintegration of a thin liquid sheet using three-dimensional numerical simulations. A double-shear layer gas flow, where a thin quiescent gas layer is sandwiched between the two fast moving gas layers, is first simulated up to a statistically steady state. The downstream dynamics of the gas shear layers shows vortex shedding and three-dimensional rib-like vortical structures, similar to the wake of a bluff body. This gas flow is then used as the initial condition for a liquid-gas simulation, where the liquid phase is sandwiched by the top and bottom fast gas streams. A thin liquid sheet with a thickness of 25 mu m is considered using air/water conditions. The liquid sheet oscillates and small holes, preceded by craters surrounded by ripples, are formed. The thinning of the liquid sheet, spanwise corrugations, and vortex separations within the liquid-gas boundary layer are shown to govern the dynamics of the liquid sheet. A localized pressure jump is also observed inside the liquid sheet and precedes the rupture of the liquid sheet by pushing the liquid away in the span direction. The holes formed subsequently grow in size, collide and merge with each other, and break the liquid sheet into multiple droplets.