Fluid Mechanics and Acoustics Laboratory - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique

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Flows generated by ultrasound waves

Flows generated by ultrasound waves

Sophie Miralles, Valéry Botton, Séverine Millet, Daniel Henry, Hamda Ben Hadid, S. Kaddeche

Propagation of acoustic waves in a fluid can lead to the creation of a large scale steady flow known as acoustic streaming. We are principally interested by the Eckart streaming for which the flow is created inside the fluid by the Reynolds stresses resulting from the action of the acoustic wave. These flows can be used to stabilize certain situations or in contrast to favor instationnarities and chaos and promote mixing.

Video showing the onset of the flow by acoustic streaming.

An experiment in water has been developed in our team: the objectives are to measure the characteristics of Eckart streaming in connection with the properties of the acoustic field and to show its effect on the instabilities in a heated fluid. Interesting results have been obtained on the characteristics of the acoustic streaming jet, in the near-field and in the far-field zones, and on the oscillations which could occur. A model has been developed, which allows to obtain good comparisons between the numerical results and the experimental measurements [A111, A112, A115] (PhD of B. Moudjed).

Video showing the oscillation of the jet (up: longitudinal component of the velocity, down: transverse component).

The flow created by an acoustic beam reflected on a glass wall has also been analyzed experimentally and numerically. Good comparisons have been obtained [A118].

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Flow generated by a reflected acoustic beam (experimental results).

A four jet situation corresponding to three successive reflections of the acoustic beam on the walls, has then been studied experimentally and numerically. We were particularly interested by the transition towards chaotic states [A128, A131].

Video showing the oscillation of a four jet situation corresponding to three successive reflections of the acoustic beam on the walls (numerical simulation showing the velocity perturbations (arrows and colored iso-values) and the mean jets (black iso-value)).

Older work: stabilization of convection by acoustic streaming.

We also studied the effect of the Eckart streaming on the instabilities in the Hadley flow. For small ultrasound beam widths, the flow is destabilized, whereas for larger widths, stabilizing effects can be obtained. Stabilization can be favored by an adequate decentring of the beam [A77, A92, A97]. Simulations using continuation methods in a 3D heated cavity with dimensions 4x1x1 show that, in this situation too, the oscillatory transition can be stabilized by the Eckart streaming. The stabilizing effect has been shown to depend on the cavity length and on the Prandtl number [A85, A88] (thesis of W. Dridi). We also studied the stabilizing effect that could be obtained by Eckart streaming in the Rayleigh-Bénard situation [A102].