Mechanisms of the suppression of stimulated sound scattering in liquids and gases

Equations describing the propagation of a weak acoustic wave against the background of an intense pumping wave are obtained in the context of geometrical acoustics, with allowance made for the excitation of relaxation modes, including quasi-stationary entropy waves and vorticity. The effect of acoustic flow induced by an excitation beam is investigated in detail. It is shown that, due to the inhomogeneity of acoustic flow, the low-frequency acoustic pulsations may resonate with the relaxation modes only in a narrow zone of the interaction region. This leads to a sharp drop in the integral increment, and stationary scattering cannot compete with the pumping wave harmonic generation. The possibility of the observation of this type of scattering in the nonstationary regime is assessed.