Nonlinear sound scattering of crossed focused beams in the presence of turbulence—Angular measurements

Abstract

Experiments are performed involving the interaction of mutually perpendicular crossed, ultrasonic beams overlapping (at a common focal point) and interacting in the presence of turbulence generated by a d = 0.64‐cm‐diam submerged water jet (Re = 8.5 × 105). Measurements of the radiated sum‐frequency intensity, Doppler shift, and‐spectral broadening are recorded from the scattered spectra. In the absence of turbulence, no sum frequency can be detected. The two cw primary beams (f1 = 1.9 MHz, f2 = 2.1 MHz) are generated by individual transducer units of 15.2‐cm focal length. The receiver (a circular plane array located outside the interaction region) is positioned with its axis perpendicular to the jet at a distance of 30d from the nozzle (the interaction region). Previously, very good theoretical predictions of mean flow and rms turbulent velocity were determined from the Doppler shift and spectral broadening data from a similar crossed‐beam scattering experiment [M. S. Korman and R. T. Beyer, J. Acoust. Soc. Am. 84, 339–349 (1988); 85, 611–620 (1989)]. The primary beams were generated by circular plane array elements. Results suggested that the interaction involved an averaging across a large region of flow. The localized crossed‐beam interaction region allows turbulent flow properties to be predicted with reasonable spatial resolution. [Work supported by the Naval Academy Research Council.]