Author(s): K. V. Rao; S. T. Hall
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Keywords: No Keywords
Abstract: The stability of laminar flow in a 90°triangular open channel was investigated experimentally. The critica1 Reynolds number (based on average velocity and slant depth of flow in the channel) at which the flow became unstable giving abrupt transition to turbulence was established. The most striking feature of this abrupt transition in the present investigation was the rapid development of instability into ful1y developed turbulent aotion. The instability manifested itseif with the sudden appearance of free surface disturbances, generated in the channel near the entry. The disturbances were intermittent and had the appearance of flashes or bursts of turbulence. The turbulent bursts were observed to be almost periodic. These bursts of irregularities were carried down the channel separated by short lengths of smooth surface. The bursts ' length depended on flow rate and a small increase in the flow changed entire length of the channel to turbulent flow. In order to determine the structure of the flow so as to distinguish the type of motion, the velocity profiles were measured using the Laser Doppler Anemometer techniques. The characteristic feature of the abrupt transition in the flow phenomenon and the resulting secondary flow patterns were observed by means of photographic technique. The resistance to flow was determined and this also clearly illustrates the occurrence of abrupt transition to turbulence in open channels.
Year: 1985