Production of Sounds in Distensible Tubes

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Abstract
A photocell was used to record vibrations in a solution of white Hector bentonite passing through a constriction introduced into Tygon or cellophane tubing, or into a transparent flat flow section with distensible sides. These vibrations were compared with those simultaneously recorded from the walls of the model. Both vibration spectra were also subjected to frequency analysis. At low steady flow rates in either three-dimensional system, the jet lost its laminar characteristics downstream from the constriction, but this disturbance was not accompanied by wall vibrations. At somewhat higher flow rates, the eddies impinged upon the walls and set up local wall vibrations, below the audible range. At still higher velocities, the turbulence became greater and the wall vibrations spread along the walls and became audible. However, the frequencies of the fluid motion did not necessarily appear in the frequency spectrum of the walls. The amount of energy necessary to set the walls in motion was partly determined by their physical characteristics; vibrations were more easily produced in the thin, flexible cellophane than in the thicker Tygon. Thus, the absence of murmurs does not mean that flow is laminar nor does the presence of wall vibrations mean that they are audible.