Numerical Modeling and Verification of Acoustic Streaming Induced by Ultrasonic TreatmentD. Rubinetti , D. A. Weiss , J. Müller , A. Wahlen ,
 Institute of Thermal and Fluid Engineering, University of Applied Sciences Northwestern Switzerland, Windisch, Switzerland
 Institute of Product and Production Engineering, University of Applied Sciences Northwestern Switzerland, Windisch, Switzerland
Acoustic streaming (AS) describes a physical phenomenon where an oscillating sound emitter induces a steady fluid motion. Metal processing industry applies this treatment for grain morphology adjustments during the solidification of metal. Improvement and further development of this technique focus on numerical modeling to reduce substantial costs for test rigs and field tests.
This study presents a numerical model which takes the acoustics and fluid dynamics in a coupled way into account. The oscillating sonotrode is placed into the fluid, creating a time-averaged harmonic sound pressure field. A force term based on attenuation of sound waves due to viscous effects acts on the fluid inducing the steady fluid motion.
COMSOL Multiphysics® is used to carry out the simulations. The acoustic pressure field is evaluated with the Pressure Acoustics, Frequency Domain interface featuring an additional source term to include sound attenuation. By means of a force term correlation, the resulting time-averaged particle velocities are implemented as driving forces in the Laminar Flow interface. In order to correctly incorporate law of mass conservation, weak contributions are defined.
The results have been experimentally validated with a small scale laboratory model using water, seed oil and glycerin as fluid. The presented concept for the numerical modeling of AS is numerically stable and accurate. It can be transferred to related applications involving sound driven fluid motion.