Aspects of super to subcritical flow transition without a jump

Abstract

2In some cases, the flow head loss is not the main concern of design engineers, who instead prefer to exclude the hydraulic jump from super-to subcritical flow due to unfavourable flow conditions. The present study investigates the flow field and hydrodynamic aspects of the transitional region from super-to subcritical flow without a hydraulic jump. It is found that inside the transitional region the velocity and pressure profiles deviate slightly from uniform flow velocity and hydrostatic pressure. According to evaluation of the velocity measurements in conjunction with the continuity equation, the characteristics of the transitional region are determined. Furthermore, Reynolds stresses are analysed and the mechanisms of transition from super-to subcritical flow without a jump are demonstrated qualitatively. Results relating to the profiles of shear stresses, vorticity and the total angular momentum along the transition are developed. Results indicate that the first short part of the flow field downstream of the transition structure floats on the incoming high-speed fluid where the shear stress is maximal. It is observed that, downstream of the structure, both the shear stresses and the vorticity are maximal along the streamlines. Inside the shear layer, the vorticity spreads upward by diffusive mechanisms.

Editorial

“…This problem is tackled in detail by Kabiri-Samani and Naderi (2017), who used a set of experiments under carefully controlled conditions in which they adopted a transitional structure to force a change in flow regime, taking vorticity, angular momentum and shear stress into account. Again there is a reliance here on both advanced computational techniques to analyse the data and on state-of-the-art sensors (acoustic Doppler velocimeters and pressure transducers) to produce accurate results.…”