Experimental studies of impulse noise produced by spheres moving through water

It is known from previous experiments that freely falling spheres produce sudden noise bursts. The source of this noise is unknown and little is known about the conditions under which it occurs, In an attempt to study this phenomenon under controlled conditions, spheres were towed in an anechoic tank. Velocities up to 5 m/sec and Reynolds numbers up to 4 x 10/5 were obtained with spheres of 2", 4" and 10" diameter. After eliminating all mechanical and acoustical disturbances, no noise bursts could be detected, However, the impulsive noise was still observed in free-fall experiments, and a ranging system allowed the location of these noise bursts with respect to a fixed point. A frequency analysis was done with a digital signal processor.http://archive.org/details/experimentalstud00kunzLieutenant Commander, Federal German NavyApproved for public release; distribution is unlimited