Experimental dynamics of Newtonian and non-Newtonian droplets impacting liquid surface with different rheology

Abstract

A high-speed visualization is used to study the droplet impact dynamics exhibiting diverse rheological characteristics covering Newtonian, shear thinning, and viscoelastic characteristics on a liquid pool. The series of experiments covers a series of physical non-dimensional parameters such as 10 < Re < 12 000, 298 < We < 768, 0.034 < Ca < 39.7, and 1.8 × 10−3 < Oh < 3.4. The Reynolds number and the Weber number are the most important non-dimensional parameters to describe the dynamics of the generated crown structure. The Ohnesorge number and the Weber number play important roles in the stability of the Worthington jet. The normalized time of the Worthington jet breakup follows power law dependency to the Ohnesorge number (tbreakuptvisc≈Oh−1) and to the Weber number (tbreakuptR≈We2). Coalescence has strong effects on the dynamics of droplet impact. Impact dynamics depends on rheological characteristics of the droplet and liquid pool (i.e., impact dynamics of the water droplet on the shear thinning pool is different from the shear thinning droplet onto the water pool). Rate-dependent shear viscosity and extensional viscosity have strong effects on the droplet impact dynamics by avoiding instability along the rim of the crown. Viscoelastic droplet impact dynamics, presented by Ec ≈ 212 (larger elastic vs viscous forces) and De ≈ 2.2 (larger elastic vs inertia forces), reveals a strong stabilizing effect of elastic stress on the Worthington jet structure by avoiding the jet breakup and, instead, forming a thin filament connecting the jet and the satellite droplets. The stabilizing effect of elastic stress is higher than that of viscous stress.