Hydrodynamic Droplet Levitation on Rotating Disks: Experimental and Computational Approach

Droplet-surface interactions are vital for industrial processes like spray coating and cooling. While the thermal Leidenfrost effect levitates droplets on a vapor cushion, similar non-wetting behavior is achievable hydrodynamically at ambient temperatures. A moving surface submerged in a fluid generates a boundary layer that can prevent an impacting droplet from making direct contact. This investigation presents a combined experimental and computational fluid dynamics (CFD) analysis of a liquid droplet interacting with the boundary layer from a vertically rotating flat disk. The experimental goal was to achieve stable droplet levitation in both laminar and turbulent boundary layers. We also sought to define the operational limits by identifying the critical impact velocity where a free-falling droplet penetrates the boundary layer and contacts the disk. The computational work describes the complex flow field around a levitating droplet. We analyze the interaction between the rotating disk flow and the stationary droplet, quantifying changes to the base flow and the resulting aerodynamic forces. This analysis also explains the origin of observed droplet shape oscillations by examining flow instabilities and their effect on the pressure distribution across the droplet's surface. This dual approach provides a detailed understanding of the physics governing hydrodynamic droplet levitation.