Hydraulic jumps at drop and abrupt enlargement in rectangular channel

Abstract

The different types of hydraulic jumps that occur in a rectangular channel at an abrupt increase in section are experimentally studied. The abrupt section increase is due to both a drop and an increase in the channel width. Experiments were carried out with three different values of the ratio L/l between the channel widths respectively downstream and upstream of the abrupt section increase. For each L/l value five values of Froude number F₁, of the supercritical flow upstream of the section increase were considered, and for each of them live values of the depth y₁ of the same flow. The experiments showed that, as the depth y₂ of the downstream subcritical flow increases, several types of hydraulic jumps occur. The sequence of hydraulic jump types and several characteristics of hydraulic jumps of the same type change with the flow parameters L/l, F, and s/y₁, with s the drop height. Physical explanations of these changes are proposed, based on both direct observation of phenomena and comparison with results of other authors relative to the cases of either drop only or enlargement only.