SOUND SCATTERING FROM A PARTICLE-LADEN, TURBULENT JET

Multifrequency acoustic scattering experiments were carried out in the laboratory using a free, turbulent water jet carrying solid particles in suspension. A crossed-beam geometry was used, in which the axis of the jet was perpendicular, or nearly so, to the direction of the incident sound. The suspended particles were either natural sand grains or lead-glass beads, 100-500-mu-m in diameter. The results, based on measurements made simultaneously at 1, 2.25, and 5 MHz, include backscatter and attenuation as a function of suspended sediment concentration. measurements of the total scattering and backscattering cross sections of natural sand grains and glass beads as a function of frequency and particle size, and two-point correlation measurements of the fluctuations in apparent suspended sediment concentration. The lead-glass bead cross sections exhibit both the resonance and diffraction extrema expected of solid spherical scatterers; the sand cross sections do not and, for acoustic wavelengths comparable to or less than the particle circumference, are larger than spherical scatterer theory would predict. The two-point correlation estimates of jet velocity and measurements of the time-averaged jet width as a function of particle size are related to the mean and turbulent structure of two-phase jets and illustrate the potential of acoustic methods for noninvasive investigations of two-phase turbulent flow.