The cavitation field radiated by a 20 kHz sonotrode-type transducer is experimentally and theoretically analyzed. Special interest is paid to the origin of the strong fluid streaming appearing in low frequency sonoreactors. A new experimental procedure is proposed to evaluate the mean acoustic pressure inside the fluid. This parameter has been quantified for different points and amplitudes. The velocity of the radiating surface is controlled by a laser interferometer and is always sinusoidal. Train wave excitation is used. The pressure wave and amplitude are measured in the tank with a calibrated hydrophone. The acoustic mean pressure is estimated from the total pressure value at the end of the pulse after an adequate filtering. An analytical nonlinear second order model based on the coupling of the equations of the fluid mechanics with the Rayleigh-Plesset equation is developed in order to relate the measured acoustic parameters to the cavitation state of the fluid. The distributions of the fundamental amplitude and mean pressure are calculated as a function of bubble density and bubble size. A qualitative theoretical description of the experimental data is presented. Quantitative differences and model limitations are commented.

The cavitation field generated by an ultrasonic horn at low frequency and high power is known to self-organize into a conical bubble structure. The physical mechanism at the origin of this bubble structure is investigated using numerical simulations and acoustic pressure measurements. The thin bubbly layer lying at horn surface is shown to act as a nonlinear thickness resonator that amplifies acoustic pressure and distorts acoustic waveform. This mechanism explains the self-stabilization of the conical bubble structure as well as the generation of shock wave and the focusing at very short distance.

During acoustic cavitation process, bubbles appear when acoustic pressure reaches a threshold value in the liquid. The ultrasonic field is then submitted to the action of the bubbles. In this paper we develop a model to analyze the cavitation phenomenon in one-dimensional standing waves, based on the nonlinear code SNOW-BL. Bubbles are produced where the minimum rarefaction pressure peak exceeds the cavitation threshold. We show that cavitation bubbles appear at high amplitude and drastically affect (dissipation, dispersion, and nonlinearity) the ultrasonic field. This paper constitutes the first work that associates the nonlinear ultrasonic field to a bubble generation process.