Transition of super-to subcritical flow without a hydraulic jump by a cross-sectional transition structure

Abstract

Shock waves complicate the design of hydraulic structures, involving the transitions in a channel with supercritical flow regime. Abrupt changes in characteristics of a supercritical flow, e.g., in convergent transitions, would result in a rapidly varied flow associated with a hydraulic jump, causing waves and surface fluctuations. Therefore, by applying an appropriate transition structure inside the channel, the hydraulic jump can be eliminated, and these disruptions are minimized. In the present study, an analytical/experimental investigation is conducted to design a cross-sectional transition structure CSTS, eliminating the hydraulic jump with supercritical inflow Froude numbers between 2.5 and 5.5. An analytical study was performed to design the transition structures based on the fluid shock waves theory, resulting in a conceptual design diagram for excluding the hydraulic jump from super-to subcritical flow regime. According to the results, the present CSTSs are more efficient than the corresponding bed transition structures BTSs, indicating great potential of the CSTSs to change the flow regime from super-to subcritical flow without a hydraulic jump. Flow inside the CSTSs was analyzed and the analytical results were verified, applying the present experimental measurements. Based on experimental observations, weak vortices are generated downstream of the critical section, disappearing after a fall in the water free-surface profile across the critical section.