Interaction and diffraction of intense acoustic beams

Abstract

The propagation of intense acoustic beams at large Reynolds numbers having a complex temporal and spatial structure is studied theoretically and experimentally. For plane acoustic waves, dispersion can be neglected in a sufficiently wide frequency range. This leads to an avalanche-like increase in the number of interacting harmonics and, as a consequence, to the formation of discontinuities in the initially continuous wave [1]. To qualitatively examine the features of the evolution of complex signals, we used the one-dimensional Burgers equation. For acoustic beams, a spatial dispersion of the wave components propagating at different angles appears, but nevertheless for sufficiently intense fields the nonlinear interaction leads to the appearance of shock fronts. The experimental technique used makes it possible to investigate the propagation of beams at large acoustic Reynolds numbers, up to 700. The results of the following cycles of experiments are discussed. A) Degenerate parametric interaction in intense acoustic beams. B) Degenerate parametric interaction of an intense acoustic pump beam and a weak signal beam on a subharmonic. C) Evolution of noise quasimonochromatic beams at large Reynolds numbers. D) Diffraction of a nonlinear beam on a flat screen.