An experimental investigation of the effect of a constriction on turbulent pipe flow

Measurements have been made of the distributions of the mean-velocity and the axial turbulence velocity component in a cross-section of a circular tube at various distances downstream from a number of different constrictions. Also spectral distributions of the turbulence velocity have been measured in the axis of the tube and in a point very close to the wall. The constrictions had a contraction ratio of 0.25 except one which had a ratio of 0.5. One of the constrictions was made of a thin rubber hose. When for this constriction the contraction ratio was reduced to a value smaller than 0.25, self-excited vibrations of the hose took place, producing an oscillating flow of the air in the tube. The Reynoldsnumber was kept at roughly 5,000. As could be expected, after 40 tube diameter distance downstream from the constrictions an almost complete recovery of the disturbed turbulent flow, as far as the distributions of the mean velocity and relative turbulence intensity are concerned, was obtained. Depending on the shape of the constriction even a shorter distance appeared to be sufficient. The flexible constriction then was in the non-vibrating condition. However, the spectral distributions showed in some cases still a difference with the undisturbed case, in particular in the low frequency range. If the flexible constriction was vibrating, the induced oscillations of the flow which showed up as discrete peaks in the spectral distributions, persisted over the entire length of the tube, again as expected.