High-speed oblique drop impact on thin liquid films

Abstract

We numerically investigate high-speed drop impact on thin liquid films with a focus on oblique impact. The flow behavior is described by solving the incompressible Navier-Stokes equations using the variable density pressure projection method. The phase interfaces are captured using the momentof-fluid method. The numerical method is validated against experiments and theoretical predictions. Our study on high-speed oblique impact reveals that the tangential velocity can significantly alter impact phenomena: a higher tangential velocity leads to a lower lamella height and radius on the side behind the advancing drop, and the higher tangential velocity also leads to stronger vortices at the drop and film interface due to Kelvin-Helmholtz instability. Our investigation on the effect of liquid film thickness shows that a thinner liquid film leads to an earlier crown breakup. Last, our study shows that lowering the film density can prompt earlier splashing.

Toward direct numerical simulation of high speed droplet impact

“…Two grid sizes have been tested with the CMOM algorithm : no difference is shown on drop diameter ( Fig.9). This is consistent with the results obtained by Guo and Lian [25], who showed a weak varia- tion on this variable with resolution higher than 62 cells per diameter, and concluded on a converged simulation. However, some clear differences appear when looking at crown profile: on the fine grid, jetting is observed during crown elevation and a myriad of secondary droplets are produced, while on the coarse grid instabilities occur only when the crown is well developed (Fig.…”

“…D " 3.82 mm´U D " 3.94 m.s´1´h f ilm " 2.57 mm´Re l " 8400´W e " 8200 Crown diameter measured at the base of the rim. Data measured by Cossali[23], results from present 3D simulations (CMOM and LS methods), results obtained by Guo & Lian[25], Yarin & Weiss model[24].…”

“…The widespread model of Yarin & Weiss [24] has been plotted and, as remarked by Cossali, do not fit the experimental data, even if used in its presumed validity domain. This arises as a warning signal and remind such model or correlation should be used as a predictive tool in exploratory configuration with extra caution [25].…”

“…However, splashing phenomenon has only been barely addressed using 3D direct numerical simulation due to high costs involved in such calculation. In 2018, Guo & Lian [25] proposed some high-velocities impact calculations, showing that current hardware resources now enable the community to address this problem.…”

Simulation of high-speed droplet impact against a dry/wet rigid wall for understanding the mechanism of liquid jet cleaning

“…3,16,17 However, this evaluation is insufficient to identify the mechanism of the particle removal. With regard to the study of the droplet impact against a rigid wall, large variety of acoustic and hydrodynamic phenomena have been investigated (e.g., water hammer [18][19][20][21][22] , cavitation [23][24][25] , splashing [26][27][28][29][30][31][32] , side jetting 21,33,34 and rim instability 35,36 ). However, it is challenging to experimentally measure the wall shear flow development and visualize the particle removal.…”