Dynamics of an acoustically levitated fluid droplet captured by a low-order immersed boundary method

We present a variant of the immersed boundary (IB) method that implements acoustic perturbation theory to model acoustically levitated fluid droplets. Instead of resolving sound waves numerically, our hybrid method solves acoustic scattering semi-analytically to obtain the corresponding time-averaged acoustic forces on the droplet. This framework allows the droplet to be simulated on inertial timescales of interest, and therefore works with much larger time steps than traditional compressible flow solvers. To benchmark this technique and demonstrate its utility, we implement the hybrid IB method for a single droplet in a standing wave. Simulated droplet shape deformations and streaming profiles agree with available theoretical predictions. Our simulations also yield insights into the streaming profiles for elliptical droplets, for which a comprehensive analytic solution does not yet exist.