Nonlinear hydrodynamic effects induced by Rayleigh surface acoustic wave in sessile droplets

M. Alghane, B. X. Chen, Y. Q. Fu, Y. Li, M. P. Y. Desmulliez, M. I. Mohammed, and A. J. Walton
Phys. Rev. E 86, 056304 – Published 9 November 2012

Abstract

We report an experimental and numerical characterization of three-dimensional acoustic streaming behavior in small droplets of volumes (1–30 μl) induced by surface acoustic wave (SAW). We provide a quantitative evidence of the existence of strong nonlinear nature of the flow inertia in this SAW-driven flow over a range of the newly defined acoustic parameter FNA=Fλ(σ/Rd)0.01, which is a measure of the strength of the acoustic force to surface tension, where F is the acoustic body force, λ is the SAW wavelength, σ is the surface tension, and Rd is the droplet radius. In contrast to the widely used Stokes model of acoustic streaming, which generally ignores such a nonlinearity, we identify that the full Navier-Stokes equation must be applied to avoid errors up to 93% between the computed streaming velocities and those from experiments as in the nonlinear case. We suggest that the Stokes model is valid only for very small acoustic power of 1 μW (FNA<0.002). Furthermore, we demonstrate that the increase of FNA above 0.45 induces not only internal streaming, but also the deformation of droplets.

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  • Received 18 November 2011

DOI:https://doi.org/10.1103/PhysRevE.86.056304

©2012 American Physical Society

Authors & Affiliations

M. Alghane1,2, B. X. Chen1,*, Y. Q. Fu1,3,†, Y. Li4, M. P. Y. Desmulliez1, M. I. Mohammed1, and A. J. Walton4

  • 1School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
  • 2Mechanical Engineering Department, Engineering College, University of Omar Al-Mukhtar, Al Bayda, Libya
  • 3Thin Film Center, Scottish Universities Physics Alliance (SUPA), University of West of Scotland, Paisley PA1 2BE, Scotland
  • 4Institute for Integrated Systems, Scottish Microelectronic Center, Institute for Integrated Micro and Nano Systems, School of Engineering, University of Edinburgh, Edinburgh EH9 3JF, United Kingdom

  • *Corresponding author: b.chen@hw.ac.uk
  • Corresponding author: richard.fu@uws.ac.uk

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Vol. 86, Iss. 5 — November 2012

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