Reverse Steady Streaming Induced by a Freely Moving Wavy Wall

In this work, we present a theoretical and experimental investigation of the fluid–structure interaction between a freely moving wall and an oscillatory flow. Our objective is to elucidate the coupling mechanism between the fluid and the oscillating body that gives rise to reverse streaming, that is, the reversal in the rotation direction of the resulting steady vortices, and to apply this analysis to the case of a freely moving wavy wall. The flow is analyzed theoretically based on a two-dimensional model and an analytical solution is obtained using a perturbation method. Experimental results based on Particle Image Velocimetry are also presented, where an oscillatory flow generated by an electromagnetic force in an electrolyte layer drives a wavy wall floating on the surface. The results confirm the occurrence of reverse streaming and demonstrate that the flow dynamics depend on the density ratio between the freely moving solid and the fluid. The analytical solution qualitatively captures the streaming reversal observed in the experiments.