title: Nonlinear hydrodynamic effects induced by Rayleigh surface acoustic wave in sessile droplets.
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 F{NA}=Fλ/(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.
authors.affiliation: School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Alghane
authors.forename: B X
authors.initials: BX
authors.lastname: Chen
authors.forename: Y Q
authors.initials: YQ
authors.lastname: Fu
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: M P Y
authors.initials: MP
authors.lastname: Desmulliez
authors.forename: M I
authors.initials: MI
authors.lastname: Mohammed
authors.forename: A J
authors.initials: AJ
authors.lastname: Walton
mesh_terms: D003198:Computer Simulation; D057446:Hydrodynamics; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D012212:Rheology / Q000379:methods*; D012542:Scattering, Radiation; D012996:Solutions / Q000737:chemistry*; D013016:Sound; D014867:Water / Q000737:chemistry*
chemical_list: D012996:Solutions; D014867:Water