Hydraulic Jump Downstream of a Stepped Chute: An Experimental Study

Hydraulic jump is a rapidly varied phenomenon, in which supercritical inflow is transformed into a subcritical flow. Hydraulic jumps with a marked roller are characterized by high rate of energy dissipation and thus are frequently used as a tool for energy dissipation in spillway structures such as stilling basins. In the present study, the effect of smooth or stepped chutes on the flow properties of the hydraulic jump is investigated experimentally on a large scale facility assembled at the Laboratory of Hydraulic Constructions (LCH) of the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. The experimental set-up comprised a 30 degrees sloping, 6.0 m long and 0.5 m wide chute, followed by a 5.8 m long and 0.5 m wide stilling basin. A flap gate installed at the outlet allowed to control the tailwater level. Both smooth and stepped chute (with step heights of 3 and 6 cm) approach flow conditions were investigated for unit discharges ranging between 0.2 and 0.36 m²/s. Several flow parameters were measured, namely: inflow air concentration, flow depth and velocities; flow depths along the hydraulic jump; air concentration and velocity distributions in the hydraulic jump; dynamic pressures below the hydraulic jump. In the present paper, results and comparison between smooth and stepped chute approach flow conditions will be presented and discussed.