Early post-impact time dynamics of viscous drops onto a solid dry surface

The spreading dynamics of liquid drops normally impacting a solid dry surface at high Reynolds and Weber numbers is experimentally and numerically studied at early post-impact times starting from 10(-5) s after impact. The focus is on the emergence and growing of the axisymmetric liquid lamella underneath the drop, that is, on the time evolution of its thickness, radius, and velocity, as a function of impact velocity U and liquid viscosity nu. The Navier-Stokes equations for two-phase flows are solved numerically by an artificial compressibility method. A shock-capturing method is used for the tracking of the gas-liquid interface, neglecting surface tension effects. Experimental and numerical results are interpreted using a simple scaling analysis that reveals the characteristic lengths and velocities of the spreading dynamics. In particular, a finite characteristic time of appearance for the lamella is found, which is of the order of nu/U-2. Rescaling of the data works satisfactorily in the considered range of parameters. Thus, the lamella ejection is limited by viscosity.