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, A. J. Walton
2012 Physical Review E  
2012). Nonlinear hydrodynamic effects induced by Rayleigh surface acoustic wave in sessile droplets. Physical Review E, 86(5), [056304]. 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 F
more » ... NA = F λ (σ/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, λ is the SAW wavelength, σ 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 μW (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.
doi:10.1103/physreve.86.056304 pmid:23214873 fatcat:cyu5qtepcja2pfxip6l55sueqm