Turbulence modulation by deformable bubbles

The unique feature of multiphase flows is that the dispersed phase not only reacts to the background turbulence but also modulates and sometimes drives turbulence. In particular, a rising swarm of bubbles in an otherwise quiescent medium can actively induce turbulence, but little is known how bubbles modulate pre-existing turbulence, particularly an intense one. Intense turbulence can deform bubbles through random slip velocity and the surrounding strain. Part of the energy is left in the small-scale eddies in the wake of the bubbles, and another part is stored in the enlarged interfacial energy, which is later returned to the flow via bubble relaxation. The goal of this study is to understand this relative contribution by different mechanisms and how bubbles bypass energy cascade by pumping energy directly from large scales to small scales. Experimentally, we track dense tracers around many deforming bubbles and average the results based on the bubble orientation and the slip velocity direction. The results will shed some new light on turbulence modulation by deformable bubbles and energy cascade in turbulent multiphase flows.