Journal of Hydraulic Engineering

A two-phase air-water shear flow generated by a submerged jet and characterized by a relevant void fraction and laden with fluorescent particles has been investigated experimentally by means of particle image velocimetry (PIV) combined with the laser-induced fluorescence (LIF). Two air-water data sets have been recorded in order to explore two different regimes, namely two-way coupling and four-way coupling, according to air–water interactions. A novel robust discrimination algorithm based on the geometric features and pixel intensity of tracers and bubbles has been introduced and validated. A statistical analysis of the flow field for the two phases and of the bubble-phase geometric features and distribution has been conducted. The increase of the air-flow rate involves an upward orientation of the jet due to the interaction between the air bubbles’ buoyancy forces and the water, with a turbulence increase. Furthermore, greater interactions between air bubbles grouped in clusters occur, backed up by less variation of the air bubbles’ shape and orientation passing from the jet zone to the zone above the same. The results of this study have led to better knowledge of bubble–water and bubble–bubble interactions and to an estimation of the effects of air bubbles in the shear layer of a bubbly water jet.

In the context of the restoration of ecological continuity, it is essential to ensure that fishways be as efficient as possible. The biological efficiency of a vertical slot fishway (VSF) is highly dependent on its hydraulic design. When hydraulic conditions are not satisfied, sills (an insert that functions like a weir) are often introduced at the bottom of the slots, between the pools. In an attempt to facilitate the passage of benthic species, macroroughness (an array of blocks or boulders on the VSF bed) are positioned at the bottom of fishways. The geometry of the pools and the presence of sills or macroroughness have a strong influence on both the discharge through the pass and the flow pattern. Furthermore, the discharge coefficient, which is used by engineers to estimate the discharge through the pass, is affected by the topology of the flow. This paper provides a methodology to predict both the topology of the flow and the discharge coefficient. The methodology could be implemented in design software used to ensure the correct hydraulic performance of the device.

Hydrodynamic, computational fluid dynamics, and finite-element modeling were performed for a novel floating membrane reservoir system design for closed-loop pumped storage hydropower application. The conceptual design, which is now protected under an invention disclosure with a patent pending, offers a potential low-cost, low-impact solution to address the high costs, long investment return periods, and environmental disruptions encountered with traditional pumped storage development while offering modularity to enable replication at many locations. Prior to physical tests on a prototype, this paper documents the response analysis and modeling completed to simulate hydraulic and structural performance under different reservoir deployment and alignment arrangements, evaluate system stability, and refine the conceptual design. The results indicate that the excitation frequency from vortex shedding is at least an order of magnitude lower than the water sloshing frequencies in the reservoir, the structural natural frequency of the entire reservoir, and the vibrational frequencies of the side membranes, although excitation frequencies from other sources could cause mechanical resonance under certain conditions. To control destabilizing effects and prevent rocking motion and vibration, the authors conclude that the design could be improved by including a support structure around the floating reservoir, which could also provide floating-membrane containment, improve safety, and facilitate vertical reservoir movement. These conclusions, based on hydrodynamic and structural response modeling, help define specifications for upcoming full-scale prototype construction, deployment, and testing. This study demonstrates standard modeling technique application to an innovative design for which similar applications have not been previously evaluated. The refined design is capable of improving the scalability and feasibility of pumped storage hydropower in the United States and will be considered for commercialization following prototype testing.

Local scour on noncohesive beds caused by horizontal circular wall jets in submerged environments is investigated in this study. The effects of the ratios of sediment size-to-hydraulic radius, $K_s=d_{50}/R_h$, on the jet scour are considered. A total of 420 datasets of previous observations are compiled and 12 laboratory experiments in the $K_s$ range of 0.44–2.44 are conducted to investigate the effect of $K_s$ on scour dimensions. A dimensional analysis shows that both the particle gravity and bed resistance to the flow play important roles in the scour. Analysis on the data shows that the maximum scour dimensions vary linearly with the densimetric Froude number $F_{84}$ and nonmonotonically with a manner of a Gaussian function of $K_{\mathrm{s}}$, respectively. Finally, the formulas to predict the maximum scour dimensions of a submerged horizontal circular wall jet are proposed, which are fairly well in line with existing laboratory and field data.