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 , which is a measure of the strength of the acoustic force to surface tension, where is the acoustic body force, λ is the SAW wavelength, σ is the surface tension, and 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 μW (). Furthermore, we demonstrate that the increase of above 0.45 induces not only internal streaming, but also the deformation of droplets.
- Received 18 November 2011
DOI:https://doi.org/10.1103/PhysRevE.86.056304
©2012 American Physical Society