Journal
PHYSICAL REVIEW E
Volume 86, Issue 5, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevE.86.056304
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Funding
- Innovative electronic Manufacturing Research Center (IeMRC) through the EPSRC [FS/01/02/10]
- Carnegie Trust
- Royal Society of London [RG090609]
- Royal Society of Edinburgh
- Engineering and Physical Sciences Research Council [EP/H03014X/1] Funding Source: researchfish
- EPSRC [EP/H03014X/1] Funding Source: UKRI
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We report an experimental and numerical characterization of three-dimensional acoustic streaming behavior in small droplets of volumes (1-30 mu l) 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 F-NA = F lambda/(sigma/R-d) >= 0.01, which is a measure of the strength of the acoustic force to surface tension, where F is the acoustic body force, lambda is the SAW wavelength, sigma is the surface tension, and R-d 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 mu W (F-NA < 0.002). Furthermore, we demonstrate that the increase of F-NA above 0.45 induces not only internal streaming, but also the deformation of droplets.
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