Laboratory measurements were conducted to investigate the three-dimensional turbulent flow field around a single straight (SD) and two different T-shape groynes (TH and TF) under smooth flat-bed conditions. An acoustic Doppler velocimeter (ADV) was used in the measurements. Experimental results showed profound effects of the groyne shape on both the mean and turbulent flow characteristics, especially for the near bed region. The near bed velocity amplifications due to both of the local effects of groyne structure and constriction of the channel cross section in the SD is higher than T-shape groynes. The horseshoe vortex at the base of the SD has more compact and strong rotational momentum and lasts a longer distance downstream compared with T-shape groynes. By increasing the wing length of the T-shape groyne the flow structure at the upstream mini embayment changes from the vertical to the dominantly horizontal circulation, the horseshoe vortex disappears, and the wing segment acts as a scour coun...

In this study, the hydrodynamics of rectangular broad-crested porous weirs were numerically simulated using a nonlinear model between the pressure gradient and flow velocity through the porous medium. Computational fluid dynamics (CFD) analysis has been performed and renormalized group (RNG) $\mathrm{k}\text{-}ϵ$ model is used as the turbulence closure for Reynolds-averaged Navier-Stokes (RANS) equations. Solid and porous weirs with various properties were examined, and the drag coefficients of the porous weirs in the nonlinear flow resistance model were determined using sensitivity analysis. A logarithmic equation to determine the drag coefficient directly as a function of the hydraulic permeability is presented. By performing three-dimensional (3D) numerical simulations for a wide range of the approach discharge for different porous weir models, the discharge coefficient is described as a piecewise function of related parameters, such as head over the weir, porosity, and the grain diameter of the porous weir. Moreover, for the simulated scenarios, ratios of water passing through and over the weir are determined; consequently, new equations for the discharge ratio are developed. Finally, complex flow features over and through the different porous weirs have been expounded using developed discharge ratio curves.

In this work the performance of Reynolds Averaged Navier-Stokes (RANS) simulations to predict the flow structure developed by the presence of a sidewall obstacle in a uniform open-channel shallow flow is discussed. The tested geometry was selected due to its important role in several fluvial applications, such as the control of riverbank erosion and the creation of improved ecological conditions in river restoration applications. The results are compared against experimental laboratory velocity fields obtained after Large Scale Particle Image Velocimetry (LSPIV) measurements. It is shown that the length of reattachment of the separated shear layer generated by the obstacle is well predicted by a Reynolds Stress Model, while classical two-equation models show important limitations. All the performed RANS simulations are unable to properly predict the formation of a secondary gyre region, which develops immediately downstream the obstacle.