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Open AccessArticle

Acoustic Streaming Generated by Sharp Edges: The Coupled Influences of Liquid Viscosity and Acoustic Frequency

1
Laboratoire Interdisciplinaire des Energies de Demain, Université de Paris, UMR 8236 CNRS, F-75013 Paris, France
2
ESIEE Paris, Université Gustave Eiffel, F-93162 Noisy le Grand, France
3
Laboratoire Matière et Systèmes Complexes, Université de Paris, UMR 7057 CNRS, F-75013 Paris, France
*
Authors to whom correspondence should be addressed.
Micromachines 2020, 11(6), 607; https://doi.org/10.3390/mi11060607
Received: 11 May 2020 / Revised: 18 June 2020 / Accepted: 21 June 2020 / Published: 22 June 2020
(This article belongs to the Special Issue Acoustofluidics)
Acoustic streaming can be generated around sharp structures, even when the acoustic wavelength is much larger than the vessel size. This sharp-edge streaming can be relatively intense, owing to the strongly focused inertial effect experienced by the acoustic flow near the tip. We conducted experiments with particle image velocimetry to quantify this streaming flow through the influence of liquid viscosity ν , from 1 mm 2 /s to 30 mm 2 /s, and acoustic frequency f from 500 Hz to 3500 Hz. Both quantities supposedly influence the thickness of the viscous boundary layer δ = ν π f 1 / 2 . For all situations, the streaming flow appears as a main central jet from the tip, generating two lateral vortices beside the tip and outside the boundary layer. As a characteristic streaming velocity, the maximal velocity is located at a distance of δ from the tip, and it increases as the square of the acoustic velocity. We then provide empirical scaling laws to quantify the influence of ν and f on the streaming velocity. Globally, the streaming velocity is dramatically weakened by a higher viscosity, whereas the flow pattern and the disturbance distance remain similar regardless of viscosity. Besides viscosity, the frequency also strongly influences the maximal streaming velocity. View Full-Text
Keywords: acoustofluidics; microfluidics; acoustic streaming; sharp edge; particle image velocimetry acoustofluidics; microfluidics; acoustic streaming; sharp edge; particle image velocimetry
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MDPI and ACS Style

Zhang, C.; Guo, X.; Royon, L.; Brunet, P. Acoustic Streaming Generated by Sharp Edges: The Coupled Influences of Liquid Viscosity and Acoustic Frequency. Micromachines 2020, 11, 607.

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