Numerical simulation of acoustofluidic manipulation by radiation forces and acoustic streaming for complex particles

Abstract

The numerical prediction of acoustofluidic particle motion is of great help for the design, the analysis, and the physical understanding of acoustofluidic devices as it allows for a simple and direct comparison with experimental observations. However, such a numerical setup requires detailed modeling of the acoustofluidic device with all its components and thorough understanding of the acoustofluidic forces inducing the particle motion. In this work, we present a 3D trajectory simulation setup that covers the full spectrum, comprising a time-harmonic device model, an acoustic streaming model of the fluid cavity, a radiation force simulation, and the calculation of the hydrodynamic drag. In order to make quantitatively accurate predictions of the device vibration and the acoustic field, we include the viscous boundary layer damping. Using a semi-analytical method based on Nyborg's calculations, the boundary-driven acoustic streaming is derived directly from the device simulation and takes into account cavity wall vibrations which have often been neglected in the literature. The acoustic radiation forces and the hydrodynamic drag are calculated numerically to handle particles of arbitrary shape, structure, and size. In this way, complex 3D particle translation and rotation inside experimental microdevices can be predicted. We simulate the rotation of a microfiber in an amplitude-modulated 2D field and analyze the results with respect to experimental observations. For a quantitative verification, the motion of an alumina microdisk is compared to a simple experiment. Demonstrating the potential of the simulation setup, we compute the trajectory of a red blood cell inside a realistic microdevice under the simultaneous effects of acoustic streaming and radiation forces.

Comparing methods for the modelling of boundary-driven streaming in acoustofluidic devices

“…However, in most practical experimental acoustofluidic manipulation devices (not including SAW devices, see below), where 1D or 2D standing wave fields are established and 3D models are required to solve the acoustic and streaming fields, the LVM can be effectively applied as the channel dimensions are usually many orders of magnitude larger than the acoustic boundary layer thickness and typically only the acoustic streaming fields outside the acoustic boundary layer are of interest. This can further explain the good consistency between the experimental measurements in acoustofluidic manipulation devices and the results simulated from the LVM in 3D models presented in the literature recently (Lei et al 2013(Lei et al , 2014a(Lei et al , b, 2016Hahn et al 2015).…”

“…On the one hand, 2D modelling of classical boundary-driven streaming has shown good consistency with theoretical solutions (Kawahashi and Arakawa 1996;Aktas and Farouk 2004) and with experimental measurements (Augustsson et al 2011;Muller et al 2012Muller et al , 2013. On the other hand, most recently, computationally efficient methods have allowed three-dimensional (3D) simulations of boundarydriven streaming (Lei et al 2013(Lei et al , 2014a(Lei et al , b, 2016Hahn et al 2015), enabling the demonstration of complex 3D characteristics of acoustic streaming flows and leading to an understanding of the driving mechanisms of streaming patterns experimentally observed in many practical acoustofluidic manipulation devices (Hagsater et al 2007;Hammarstrom et al 2012). …”

Leveraging collective effects in externally driven colloidal suspensions: experiments and simulations

“…Optimizing acoustically-driven suspensions will require the assistance of theory and numerical simulations, as in these systems inertia must taken into account. Numerical tools have been developed at the individual or pair level [111,172,173,105,112,107,115], but further development is necessary to simulate suspensions including the effects acoustic streaming, hydrodynamic interactions, and shape asymmetry.…”

Advances in Micromanipulation Actuated by Vibration-Induced Acoustic Waves and Streaming Flow

“…BAW devices usually have a certain depth and stable propagation medium. BAW devices have viscous boundary layers at the fluid cavity walls that cause boundary-driven streaming on the boundary parallel to the propagation direction [25]. The existence of boundary streaming restricts the wave's propagation in the boundary direction, which generated concentrated acoustic waves.…”