Characterizing bulk-driven acoustic streaming in air

Abstract

The time-independent fluid flows induced by the attenuation of acoustic energy known as acoustic streaming have been experimentally measured in air using particle image velocimetry for two high powered ultrasonic transducers. The literature declares that these bulk-driven “Eckart” streaming flows are observed as turbulent jets in the direction of the acoustic wave propagation. The aim of this work is to increase the understanding of the coupling between the acoustic and fluid domains and to validate these well-established theoretical relationships. Langevin horns and focused arrays of parking sensor transducers, which operate at ∼26 and 40 kHz, respectively, and are both capable of producing sound pressure levels of up to 170dB, were used to assess the relationship between the first order acoustic field and the second order streaming velocity field. Streaming velocities of the order of 0.2 and 0.3 m/s were measured for the Langevin horn and the focused array, respectively. Two-step COMSOL Multiphysics models were created for both transducers, first solving the acoustic fields in the frequency domain, then using the results to drive a streaming volume force in a stationary fluid mechanics study. Both laminar and turbulent k-ε fluid mechanics models were compared to the experimental results.