Acoustic streaming jets in liquids

Theoretical and experimental investigations of acoustic streaming jets in water are described. The jet is produced by a plane circular ultrasonic transducer in a cavity inside a water tank, either in the near field or in the far field of the acoustic beam. The approach combines an experimental characterization of both the acoustic field and the obtained acoustic streaming velocity field on one hand, with both scaling analysis and CFD using an incompressible Navier-Stokes solver on the other hand. It is shown that good comparisons between experimental and numerical results can be obtained with a theoretical model based on a linear acoustic propagation model accounting for diffraction coupled to a hydrodynamic model including inertia effects. The coupling is obtained by the introduction of a momentum source term, the acoustic streaming force, in the hydrodynamic model. Both experimentally and numerically, the shape of the flow is thus found to be directly affected by both the overall shape of the acoustic beam and the local variations in acoustic pressure amplitude, in particular in the acoustic near field. Through scaling analysis, two scaling laws featuring linear or square root variations of the streaming velocity level with the acoustic power have been found. These scaling laws are shown to apply with a reasonable agreement to our numerical and experimental data, as well as to other former experimental investigations found in the literature.