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The characteristics of air entrainment in hydraulic jumps below a sluice gate were systematically investigated. The air entrainment region is divided into the advective diffusion region and the breaking region. For the advective diffusion region, it was found that the air concentration for a fully developed inflow is larger than that for an undeveloped inflow under a given inflow Froude number. For a partially developed inflow, the air concentration in the advective diffusion region depends on the boundary layer development of the supercritical inflow. The air concentration in the breaking region is nearly independent of the inflow conditions of the boundary layer development. Regarding the effect of the inflow Froude number, the air concentration in both the advective diffusion and breaking regions increases with the inflow Froude number under a given boundary layer development. The air entrainment mechanism in jumps is explained for both the advective diffusion and breaking regions. [ABSTRACT FROM PUBLISHER]

Knowledge of hydrodynamic processes is essential for engineers who assess the stability of energy dissipation structures undergoing extreme pressure fluctuations caused by turbulence during high discharge. Methods are in particular required to evaluate the frequencies of occurrence of extreme pressures. This work explores the use of the generalized extreme value (GEV) distribution to represent frequencies of instantaneous pressures recorded in a structure designed for energy dissipation by a hydraulic jump in a hydroelectric power station at Porto Colombia in central Brazil. The goodness of fit of the GEV distribution was evaluated using probability plots and the Kolmogorov-Smirnov test. The results indicate that it is appropriate for studying the maximum and minimum pressures for a range of discharges corresponding to Froude numbers between 3.88 and 6.42. [ABSTRACT FROM AUTHOR]

The study of bubble clustering processes may provide a significant insight into turbulent air-water flows. Previous studies investigated these processes in plunging jets, dropshafts and hydraulic jumps. This research investigates the bubble clustering process in hydraulic jumps using experimental data collected in a rectangular horizontal flume with partially developed inflow conditions for inflow Froude numbers in the range 6.5-14.3. Two criteria for cluster identification were applied: one criterion was based upon a comparison of the local instantaneous water chord time with the median water chord time, whereas the second identified a cluster if the water chord time was smaller than the air chord time of the preceding bubble, i.e. a bubble was in the near-wake of the leading bubble. The results highlight significant patterns in clusters production both over the flow depth and the distance from the jump toe. The effect of the inflow flow Froude number on the clustering process is also discussed. [ABSTRACT FROM AUTHOR]

The undular hydraulic jump is a transitional flow phenomenon where both streamline curvature and frictional effects are important. In the past, streamline curvature effects were treated with the Boussinesq equations for the potential flow approach, thereby overlooking the real flow features. If friction is included, additional terms appear, because the specific energy variation along the undular jump is related to the boundary shear stress. However, these effects are neither addressed in the literature, nor compared with the classical Boussinesq-type solutions. Also, neither information on how boundary layer methods for adverse pressure gradients behave in undular flows is available, nor experimental data. Herein the frictional effects on the Boussinesq equations are systematically analysed using boundary layer methods for adverse pressure gradients. Based on these results, a new simplified approach is proposed to reasonably reproduce the oscillatory boundary layer characteristics in weakly undular hydraulic jumps under a steadily changing pressure gradient from adverse to favourable, and vice versa. [ABSTRACT FROM AUTHOR]

Despite being widely used for the solution of one-dimensional subcritical flows governed by Saint-Venant's equations, the Preissmann's scheme cannot solve transcritical flows. This inability is due only to the solution methods created for non-transcritical flows. Transcritical transitions present specific properties that have to be adequately represented in the numerical method. A modified version of Preissmann's method is presented herein that changes the formulation only in transcritical zones, while keeping its conservative property and shock capturing form otherwise. A solution method is proposed for the implicit system, through storing the transcritical positions. This enables to solve the system with simple and double-sweep methods. The transcritical transition problem is solved locally, either by associating the cells involved in a bore and adding an equation to characterize the information transferred into the subcritical domain, or by the addition of an internal boundary condition to characterize the expansion fan at the critical point. [ABSTRACT FROM AUTHOR]

This note presents experimental measurements on the turbulence characteristics in the transition region from the end of a hydraulic jump to open channel flow in a rectangular channel. An acoustic Doppler velocimeter was used to measure mean velocities, turbulent intensities, Reynolds stress and turbulent kinetic energy for two supercritical Froude numbers. General correlations for the variation of the normalized maximum values of the Reynolds normal stresses as well as the shear stress and the turbulent kinetic energy have been developed, using the present results and those from the literature. The supercritical Froude number was found to be an effective scale in addition to the supercritical approach flow velocity in obtaining the general correlations. [ABSTRACT FROM AUTHOR]

The article reflects on two-dimensional physical model evaluating the effectiveness of baffles and sills along with its flow characteristics and energy dissipation. Topics discussed include hydraulic jump defined by total energy dissipation rate, energy dissipation rates causing formation of vortex zones and graphs representing several spillways. Also presented is a table featuring several abbreviations used for Sharp-stepped spillway, Rounded-stepped spillway and Sill-edged spillway.