Abstract: To explore the dynamic characteristics of a thin plate draping in open channel flow and its deflection to the flow, a relationship between the flow discharge and plate angle is determined, and flow forces acting on the plate and the moments about its axis are analyzed. With the vertical pressure on the plate assumed to be hydrostatic, an analytical relationship of its deflection angle α versus the channel discharge Q is derived by the momentum theorem and its moment equilibrium. A prototype plate is tested in a U-shaped channel to verify the analytical formula derived. It shows that relative to the measurements, the error in Q calculations is less than 10% at Q > 10 L/s and less than 5% at Q > 17 L/s. Thus, the range of Q for effective measurement is 10-44 L/s. When the shape and size of the plate nearly matches the channel cross-section, a well-defined relationship exists between Q and α. As α increases, the water level drop Δh across the plate decreases gradually and approaches a fixed value (about 3 cm), and the flow under the plate changes from supercritical to subcritical flow regime. With the Reynolds number increasing, the flow resistance R of the plate increases while its resistance coefficient Cd decreases. The plate angle α is related to the drop Δh and coefficient Cd .

Key words: angle, discharge, flow resistance, drag coefficient, stress direction