Low frequency vibration induced streaming in a Hele-Shaw cell

International audienceWhen an acoustic wave propagates in a fluid, it can generate a second order flowwhose characteristic time is much longer than the period of thewave.Within a range offrequency between ten and several hundred Hz, a relatively simple and versatile wayto generate streaming flow is to put a vibrating object in the fluid. The flow developsvortices in the viscous boundary layer located in the vicinity of the source of vibrations,leading in turn to an outer irrotational streaming called Rayleigh streaming. Becausethe flow originates from non-linear time-irreversible terms of the Navier-Stokes equation,this phenomenon can be used to generate efficient mixing at low Reynolds number,for instance in confined geometries. Here, we report on an experimental study ofsuch streaming flow induced by a vibrating beam in a Hele-Shaw cell of 2 mm spanusing long exposure flowvisualization and particle-image velocimetry measurements.Our study focuses especially on the effects of forcing frequency and amplitude onflow dynamics. It is shown that some features of this flow can be predicted by simplescaling arguments and that this vibration-induced streaming facilitates the generationof vortices