ASA 126th Meeting Denver 1993 October 4-8

5aPA7. Determination of turbulent velocity correlations by the nonlinear scattering of crossed ultrasonic beams.

Murray S. Korman James E. Parker, III

Dept. of Phys., USNA, Annapolis, MD 21402

The nonlinear interaction of two, mutually perpendicular crossed ultrasonic beams, overlapping in the presence of turbulence, generates a scattered sum frequency component that radiates outside the interaction region. In the absence of turbulence, virtually no scattered sum frequency component exists (outside the interaction region). A theoretical investigation is reported that relates the shape of the ensembled averaged scattered sum frequency intensity spectrum, I[sub +] ((omega),(theta)[sub *]) (which exhibits a Doppler shift, frequency broadening, skewness, and kurtosis), to the scattering angle (theta)[sub *], incident and scattered wave vectors (where K[sub +]=k[sub s]-[k[sub 1]+k[sub 2]]), and statistical properties of the turbulent velocity field v. The n spectral moments <(K[sub +](centered dot)v)[sup n]>(proportional to)(integral)I[sub +]((omega),(theta)[sub *]) ((omega)-<(omega)>)[sup n] d(omega) (obtained from experiment) are used to evaluate turbulent velocity correlations like , where n=2. The scattering geometry involves rotating the axis of the transmitting crossed beams (which are always perpendicular to each other) in the plane containing the submerged circular water jet and receiver axes. Angle (theta)[sub *] is measured between the ray bisecting the transmitting axes and the stationary receiver axis. The crossed beams are focused and overlap at the common focal point. Spectral moments, obtained from scanning the overlap region across the jet, are used to predict velocity correlations across the width of the jet with good spatial resolution.