EXPERIMENTAL STUDY OF SUPER-CRITICAL FLOW THROUGH CHANNEL CONTRACTION

Abstract

The transitions in a channel serve as a connection between the original and the new channel. These channel transitions are a necessity in artificial or natural channels at bridges, barrages, weirs, siphons, falls, aqueducts etc. Transitions are also provided in water drains and sewage systems. The energy losses and determination of the surface profile to provide the required velocity distribution at the end of the transition are few problems areas that the hydraulic engineers need to consider. In this study, experiments were performed on a rectangular channel. The transition was contraction and expansion of the channel. It was found that for super-critical flow, till the contraction width is greater than the choking width, as the contraction width decreases the rise in water level increases and the velocity decreases. When the contraction width is reduced beyond the choking width, the water flow changes from super critical to sub critical at some distance upstream from the contraction through a small hydraulic jump. An afflux is developed, specific energy increases so that the flow can be maintained; velocity decreases abruptly some distance before the contraction. It continues to decrease till it reaches contraction.