Tests of two local optical flow techniques (Lucas-Kanade and Farneback) Application to high-velocity air-water skimming flows above a stepped chute Simultaneous comparison with phase-detection probe measurements Close agreement in terms of flow patterns and void fraction Underestimation of bubble count rate and longitudinal velocity.

In an open channel, a change from a supercritical to subcritical flow is a strong dissipative process called a hydraulic

No abstract

Traditional box culvert designs lead to development of high velocity zones in the culvert barrel that often impede upstream migration of fish. Herein, three‐dimensional Reynolds‐averaged Navier‐Stokes (RANS)‐ and Large eddy simulation (LES)‐based computational fluid dynamics (CFDs) simulations were performed to compare the effectiveness of smooth, asymmetrically roughened, and corner‐baffled barrels, in creating low‐velocity zones (LVZs) and providing opportunity for upstream passage of small‐bodied fish. The results revealed distinctive benefits provided by the asymmetrically roughened and corner‐baffled barrels relative to the smooth barrel. Cross‐sectional asymmetry, corners, and obstructions are important factors that contribute to the generation of LVZs conducive to fish passage, albeit contiguity of LVZs is required, particularly for weak swimmers. The study demonstrates the adequacy and effectiveness of CFD models to complement traditional laboratory studies in understanding basic mechanisms beneficial to fish passage and to provide insights into future designs.

In skimming flow on a stepped spillway, the upstream flow motion is non-aerated and a turbulent boundary layer develops until the outer edge of the boundary layer interacts with the free-surface: that is, at the inception point of air entrainment. Herein new experiments were performed in the developing flow region on a large size 1V:1H stepped spillway model with step height h = 0.10 m. The flow properties in the developing flow region were carefully documented. In the developing boundary layer, the velocity distributions followed a 1/4.5 th power law at step edges. Detailed velocity and pressure measurements showed some rapid flow redistribution between step edges and above step cavities. The application of the momentum integral equation indicated an average friction factor of 0.18, close to the observed air-water flow friction factor of 0.23, suggesting that the spatially-averaged dimensionless shear stress was comparable in the developing flow and fully-aerated flow regions.