The viscous effect on the transient droplet deformation process under the action of shock wave

The transient droplet deformation behaviors induced by shockwaves were experimentally recorded by high-speed shadowgraphic technique. Three Ohnesorge number (Oh) conditions (0.07, 0.32, and 0.66) andWeber number (We) ranges between 45 and 4000 were tested. Results show that the effects of viscosity on deformation are correlated with the extent of interaction inertia. At small We con-ditions, the time-dependent deformation (dc/d0) shows three stages before breakup. Initially, dc/d0 stays constant for all Oh conditions. dc/d0 increases as a function of time, and increased viscosity leads to a slower dc/d0 rate due to a higher rate of dissipation. A less viscous droplet shows a flat dc/d0 period, while for more viscous droplets, dc/d0 oscillates before breakup. For higher We cases, only the constant dc/d0 stage followed by a steady increase is observed, and higher viscous droplets still result in a lower dc/d0 increase rate in the second stage. (dc/d0)max decreases with the increase of viscosity at lowWe because the viscous dissipation consumes more inertia. However, at higherWe, (dc/d0)max increases because at this We, the increase of viscosity actually postpones the breakup, resulting in a larger (dc/d0)max. The initiation time (Tini, the time scale of droplet deformation), decreases with the increase of We due to accelerated breakup through enhanced disruptive inertia. Increased Oh lengthens this time scale because a more viscous droplet consumes the inertia faster, counteracting the effect of We. This time scale variation also explains the (dc/d0)max dependence on Oh and We.