Feasibility of Automatically Measuring of Large and Small Discharge in Open Channel Using Rectangular Sharp-Crested Weir

Rectangular sharp-crested weir used for flow measurement in flume is limited by the minimum head since head- discharge relation of clinging flow is different from free flow. Hydraulic characteristics of clinging flow under low head are studied via experiments associated with simulation in six rectangular sharp-crested weirs with different geometric parameters. The results show that head-discharge relation is stable under clinging flow; head relation between clinging and free flow is linearly correlated at the same discharge in a bistable regime, existing discharge formula of free flow can be applied to clinging flow by means of head transform; the pressure on downstream weir plate is negative, much less than atmosphere pressure, and flow regime can be judged based on the pressure. It is feasible to automatically measure large and small flow using the simplest weir without head limitation.