When an acoustic wave propagates in a fluid, it can generate a second order flow which characteristic time is much longer than the period of the wave. Within a range of frequency between 1 and several hundred Hz, a relatively simple and versatile way to generate streaming flow is to put a vibrating object in the fluid. The flow develops vortices in the viscous boundary layer located in the vicinity of the source of vibrations, which in turns leads to an outer irrotational streaming denoted as Rayleigh streaming. Due to that the flow originates from non-linear time-irreversible terms of the Navier-Stokes equation, this phenomenon can be used to move fluids and even to generate efficient mixing at low Reynolds number, for instances in confined geometries. Here we report an experimental study of such streaming flow in a Hele-Shaw cell of 2 millimeters span using long exposure flow visualization and PIV measurements. Our study is especially focused on the effects of acoustic frequency and amplitude on flow dynamics. It is shown that some features of this flow can be predicted by simple scaling arguments, invoking a balance between viscous dissipation in the boundary layer and inertia term, and that acoustic streaming facilitates the generation of vortices.
- Fluids Engineering Division
Low Frequency Acoustic Streaming in a Hele-Shaw Cell
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Costalonga, M, Peerhossaini, H, & Brunet, P. "Low Frequency Acoustic Streaming in a Hele-Shaw Cell." Proceedings of the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. Volume 1B, Symposia: Fluid Machinery; Fluid-Structure Interaction and Flow-Induced Noise in Industrial Applications; Flow Applications in Aerospace; Flow Manipulation and Active Control: Theory, Experiments and Implementation; Multiscale Methods for Multiphase Flow; Noninvasive Measurements in Single and Multiphase Flows. Chicago, Illinois, USA. August 3–7, 2014. V01BT14A008. ASME. https://doi.org/10.1115/FEDSM2014-21384
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