Study on the Control of the Hydraulic Jump by Abrupt-Rise-and-Leveled-Reverse Jet

The phenomenon of the hydraulic jump has been well known as an efficient method to dissipate the energy of high velocity flow and has been widely studied for a long time. However, as almost all Japanese rivers are very steep, particularly at points where dams are constructed, and cannot keep a reasonable tail-water depth to contain the free jump, it is usual to provide stilling basins with appurtenances such as chute blocks, sills and baffle piers to produce such tail-water depth. But, these appurtenances are very susceptible to serious damage under high velocity flow.<BR>This study investigates the possibility of controlling the hydraulic jump by an abrupt-rise-and-leveledreverse jet (Fig. 1) where in this jet system is suggested for the prevention of cavitation of appurtenances used widely in energy dissipators, for the reduction of stilling basins construction, for an increased effect of energy dissipators, and for the effective utilization of spillways.<BR>The results of this study can be summarized as follows<BR>1. It is possible to form a hydraulic jump on a horizontal floor in a stilling basin so that the ratio of the tail-water depth to initial-flow depth (ψ) decreases as the leveled-reverse jet-flow parameter increases. The analytical depth ratio computed from Eq.(6) agrees closely with the experimental depth ratio to the extent of 0 to 70% of the β_L (Fig. 10).<BR>2. The energy dissipation agrees closely with the analytical result computed from Eq.(20) to the extent of 0 to 70% of the β_L, the same as ψ(Fig. 11)<BR>3. The analytical value (β_L) obtained by the boundary condition of Eq.(13)' agrees fairly closely with the experimental reverse jet-flow parameter (β_Lexp) (Fig. 12).<BR>4. The height of the abrupt rise decreases as the reverse jet-flow parameter increases for a constant δ and F_r1. A reduction of stilling basins construction is possible (Fig. 15).<BR>5. When the Froude number of the initial flow increases for a constant α and β, the hydraulic jump forms as the aperture parameter of the reverse jets (δ) increases (Fig. 16). The more the β value increases, the more remarkable the effect of this parameter will be.<BR>This paper presents the results of an analytical and experimental study of the control of the hydraulic jump by an abrupt-rise-and-leveled-reverse jet instead of chute blocks and baffle piers. It can be concluded that this jet system is an effective method to control the hydraulic jump. Further study of this system is needed under different conditions.