Acoustic return from density fluctuations in turbulent jets

The acoustic scattering from density discontinuities in turbulent jet flows has been studied to determine the conditions under which high frequency acoustic soundings can be useful as a flow-field diagnostic tool. Laboratory experiments employing a variable-density turbulent jet exhausting into ambient water are described. The acoustic returns from the jet at 3 and 6 MHz were correlated with turbulent density fluctuation data; the acoustic data can then be extrapolated to full-scale flow situations. The study shows that field measurements of the acoustic return from a turbulent, density-stratified jet can be used to determine the flow-field properties without direct sampling or measurements in the jet. Such full-scale measurements could provide a viable technique for studying both effluent plumes in connection with pollution abatement efforts, and oceanic diffusion processes and thermocline structures. The applications of this technique to the coolant water discharge from an electric power plant, and to the flow in a stratified estuary are considered.