Numerical and theoretical modeling of droplet impact on spherical surfaces

Abstract

Droplet impact on solid surfaces is a fluid phenomenon widely involved in additive manufacturing, heat management, and coating, in which the ability to exert control over the impact dynamics and duration is critical. While past studies have established a comprehensive understanding of the impact on flat substrates, what we know about the impact dynamics on curved solid surfaces is still limited. This work aims to elucidate the physics of droplet impact on spherical targets with different radii and surface wettability using a combination of axisymmetric lattice Boltzmann method (LBM) and theoretical analysis. The model developed in our previous work [H. Dalgamoni and X. Yong, Phys. Rev. E 98, 13102 (2018)] was extended and modified for simulating the normal impact of droplet on curved substrates in the low Weber number regime, in which axisymmetric assumption of droplet deformation holds. The LBM simulations show that the surface geometry and wettability significantly affect the spreading and recoiling of droplet during impact. The parametric studies uncover five outcomes of impact, which range from complete deposition to total rebound. A simulation-predicted phase diagram was constructed and correlated with the total time that the droplet was in contact with the solid. In addition, a theoretical model based on energy budget during impact was developed to predict the rebound threshold when varying the target radius and wettability independently, which agrees well with simulation results. These findings provide fundamental insight into surface structure design for controlling droplet hydrodynamics and the contact time during impact.

Dynamics of droplet impacting on a cone

“…It was found that liquid possessed a faster retraction along the ridge than that on the flat surface, leading to a 37% reduction in contact time. 21 Following this work, studies focused on contact time reduction by asymmetric dynamics have been carried out, including the inclined surface, 22,23 curved surface, [24][25][26][27][28][29][30] surfaces with macro structures of different geometries, [31][32][33][34][35][36][37][38][39][40] moving surfaces, 41,42 and off-center impact. 43,44 Besides the aforementioned asymmetric approaches, symmetric bouncing by involving the droplet center to retraction with point-like structure to reduce contact time has also been proposed.…”

Computational and Analytical Investigation of Droplet Impingement and Spreading Dynamics around the Right Circular Cone

“…It could be estimated by using the divergence of the unit normal vector n at the interface (shown in eq 8). (8) and n is the gradient of the volume fraction at the interface, defined as (9) In eqs 6 and 7, the fluid density ρ and viscosity μ are defined by (10) (11)…”

“…In addition to its basic physics, this phenomenon is often noticed in numerous technological processes and industrial operations such as printing, coating, adhesion, fuel spraying in internal combustion engines, spray cooling/coating, casting process, chemical coating, ink-jet printing, cooling of turbine blades, pesticide, cooling of the nuclear reactor core, and so forth. Numerous experimental, numerical, and theoretical investigations on droplets impacting smooth, − flat, − curved, − and irregular , surfaces have been performed during the last few decades. Numerous investigators attempted to analyze the flow dynamics of droplet impingement on surfaces to delineate the impact dynamics.…”

Maximum spreading of droplet-particle collision covering a low Weber number regime and data-driven prediction model

“…Yoon and Shin 29 and Dalgamoni and Yong 30 investigated droplet-particle collision, focusing on effects of Weber number, surface wettability and particle size on collision behaviors and impact outcomes. Seven collision scenarios mapped against the outcome regime maps, 29 and a theoretical model for droplet rebound criterion 30 have been presented. Malgarinos et al, 31,32 Mitra et al, 33 and Mitra and Evans, 34 studied droplet collisions with a particle focusing on heat transfer and phase change behavior during a collision process.…”