Numerical investigation of drop–film interactions with a thixotropic liquid

• Published in: Journal of non-Newtonian fluid mechanics 2024-07, Vol.329, p.105259, Article 105259
• Main Authors: Steigerwald, Jonas, Ibach, Matthias, Geppert, Anne K., Weigand, Bernhard
• Format: Article
• Language: English
• Subjects: Direct numerical simulation (DNS); Drop impact; Rheomalaxis; Shear-thinning; Thixotropy; Volume-of-Fluid (VOF) method
• ISSN: 0377-0257; 1873-2631
• DOI: 10.1016/j.jnnfm.2024.105259

We investigate numerically the influence of thixotropic effects on the impact of a drop onto a thin film, a fundamental process in many technical systems. Direct numerical simulations are performed with a Volume-of-Fluid (VOF) method based multiphase flow solver whose capabilities are expanded in order to enable simulations of a thixotropic liquid. The thixotropic behavior is modeled by a rate kinetic equation for the structural integrity of the assumed microstructure of the liquid. The corresponding structural parameter is described by an additional VOF-variable. After a validation of the implementations, we vary systematically the two parameters of the thixotropic model for a selected impact scenario in order to identify thixotropic effects during the impact and on the overall impact morphology. The two parameters are the mutation number Mu=texp/tθ as the ratio of the experimental time scale to the time scale of the structural rebuilding and the parameter β, which describes the effectivity of the shear-induced structural disintegration. The parameter study leads to a regime map with three different regimes. For Mu>10, the liquid behaves purely shear-thinning. High shear rates during the early stages of the impact lead to a low apparent viscosity at the crown base and to an enhanced crown growth. For Mu