Experimental investigations of the scattering of sound by turbulence were performed in a wind tunnel. Turbulence was produced by grids of parallel circular rods (with diameters of 0.1 to 1.0 cm and grid meshlengths of 0.5 to 2. 5 cm); the sound frequencies covered a range of 100 to 500 kc. Disturbances of the measurements due to reflections of sound waves at the tunnel walls were avoided by the application of short sound pulses. The dependence of the damping of the sound waves on the sound frequency, the Mach number of the turbulence, the length of the sound path in the turbulent flow and a predominant direction of the turbulent eddies was measured. Theoretical predictions were confirmed and partly extended. In the range of the parameters which is of interest for practical use the most important results are the proportionality of the damping to the square of the sound frequency and to the square of the turbulent Mach number. Based on the measurements and the theoretical considerations, a formula is derived which is applicable to the damping of sound by turbulent scattering in the atmosphere. (Author).

Experimental investigations of the scattering of sound by turbulence were performed in a wind tunnel. Recent theoretical predictions concerning the sound attenuation are well confirmed and partly extended by the measurements. In the range of the parameters which is of interest for practical applications the most important results obtained are the proportionality of the sound attenuation to the square of the sound frequency and to the square of the turbulent Mach number. A formula is derived from which the turbulent attenuation of directed sound (such as aircraft noise in the free atmosphere) can be calculated. A method for measuring large phase variations is described in preliminary form; it will be used to investigate the influence of turbulent scattering on the phase angle of the sound waves.

The scattering of sound by the nonlinear interaction of two sound beams in the presence of turbulence is used to experimentally measure the turbulent velocities generated by a submerged water jet. When two sound beams of primary frequencies f01 and f02 intersect in a region of turbulent flow, the nonlinear scattering generates sum and difference frequency components (f0+ = f01 f02 and f0- = f01 - f02) which radiate outside the interaction region. In the absence of turbulence, the crossed beams do not produce radiated sum and difference frequencies. In this experiment, two transducers emit continuous wave focused sound beams of frequencies f01 = 2.0 MHz and f02 = 2.1 MHz, respectively. A receiving transducer, located outside the interaction region, detects the scattered sum frequency (f0 = 4.1 MHz.) Scattering results measured at 80 degree angles for each of 11 scan positions across the jet are used to map out the velocity correlation coefficients of the turbulence. Results are then compared with earlier published experiments that use conventional hotwire probes to measure a similar turbulent jet flow in air. nonlinear acoustics; sound- scattering; sound-waves; ultrasonic-waves.