Vortex Noise from Rotating Cylindrical Rods

A series of round rods of the same diameter were rotated individually about the midpoint of each rod. Vortices are shed from the rods when in motion, giving rise to the emission of sound. With the rotating system placed in the open air, the distribution of sound in space, the acoustical power output, and the spectral distribution have been studied. The frequency of emission of vortices from any point on the rod is shown to be given by the formula of yon Karman. From the spectrum, estimates are made of the distribution of acoustical power along the rod, the amount of air concerned in sound production, the “equivalent size” of the vortices, and the acoustical energy content for each vortex.