Drinking, Clapping, and Bouncing fluids

I will discuss three fluid-mechanics problems: fluid motions related to drinking, clapping, and bouncing, which you might have experienced or observed once during daily activities.

Drinking: Drinking is defined as the animal action of taking water into the mouth, but to fluid mechanists, is simply one kind of fluid transport phenomena. Classical fluid mechanics show that fluid transport can be achieved by either pressure-driven or inertia-driven processes. In a similar fashion, animals drink water using pressure-driven or inertia-driven mechanisms. For example, domestic cats and dogs lap water by moving the tongue fast, thereby developing the inertia-driven mechanism. We will investigate how cats and dogs drink water differently and discuss the underlying fluid mechanics.

Clapping: Droplets splash around when a fluid volume is quickly compressed. This phenomenon has been observed during common activities such as kids clapping with wet hands. The underlying mechanism involves a fluid volume being compressed vertically between two objects. This compression causes the fluid volume to be ejected radially and thereby generate fluid threads and droplets at a high speed. In this study, we designed and performed laboratory experiments to observe the process of thread and drop formation after a fluid is squeezed.

Bouncing: When two fluid jets collide, they can bounce off each other, due to a thin film of air which keeps them separated. We describe the stable non-coalescence phenomenon between two jets of the same fluid, colliding obliquely with each other. Using a simple experimental setup, we carry out a parametric study of the bouncing jets by varying the jet diameter, velocity, collision angle, and fluid viscosity, which suggests a scaling relation that captures the transition of colliding jets from bouncing to coalescence. This parameter draws parallels between jet coalescence and droplet splashing (crown-splash), indicating that the transition is governed by a surface instability.