Numerical investigation of the self-propulsion mechanism of a droplet on a hot ratchet surface

초록

This study presents numerical simulations to elucidate the self-propulsion of a liquid droplet on a hot ratchet surface, where complete film boiling occurs. Although the viscous mechanism is widely recognized, its role remains under debate. To precisely predict the movement of a tiny droplet on a horizontal surface, it is crucial to determine the pressure force acting on the droplet surface. Therefore, a momentum source caused by phase change was introduced in the volume-offluid method. Our analysis involved quantitatively evaluating and comparing the pressure, viscous, and vapor recoil forces acting on the droplet. The pressure force emerged as the predominant driving force behind the self-propulsion phenomenon. The direction of the viscous force was opposite to that of the droplet's advancement, challenging the conventional understanding of the viscous mechanism. The largest pressure force contributing to propulsion was generated on the rear surface of the droplet's bottom. As the droplet moved, the rear cavity opened, allowing high pressure to propagate into the region near the rear surface of the droplet's bottom. Additionally, we explored the effects of the wall temperature and tooth-inclination angle on the droplet velocity. Overall, the simulation results were consistent with the experimental observations.

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