Velocity Measurements in Transient Flow Downstream of a Submerged Vertical Drop
(EN)
Retsinis, Eugene
Papanicolaou, Panos
(EN)
ntua
(EL)
Hydraulic jumps occur when supercritical flow becomes subcritical under momentum conservation conditions and is used as energy dissipation mechanism in the design of stilling basins. In some cases a vertical negative step is constructed at the entrance of a stilling basin in order to stabilize the hydraulic jump under all operating conditions. In laboratory experiments the flow is controlled by a sluice gate upstream, and a sharp crested overflow downstream of the step. Five different rapidly varying types of flow have been observed around a step under supercritical flow conditions upstream (Moore and Morgan, 1957, Ohtsu and Yasuda, 1991, Mossa et al. 2003) The minimum B-jump is the hydraulic jump at the toe of the step, the B-jump is a submerged jump downstream of the step, the wave-train is a transient, surface jet-type flow without formation of a hydraulic jump, the wave-jump is the flow of an ascending jet forming a standing wave downstream of the step, before it dives and results in a submerged hydraulic jump, and the A-jump is the flow where the hydraulic jump is formed upstream of the step. These flow profiles appear with this sequence by increasing the tailwater depth downstream continuously. The transition from supercritical to subcritical flow over a fully submerged negative step has been studied by experiments regarding the measurement of flow depths upstream and downstream of the jump as well as the pressure at the face of the step, but not the internal turbulent flow properties in terms of velocity measurements. Aim of the present work is the measurement of the two-dimensional velocity field in the region of a wave-train using Particle Image Velocimetry (PIV) for three upstream Froude numbers 1.99, 2.55 and 2.99.
(EN)
