Modeling flows over gravel beds by a drag force method and a modified S–A turbulence closure

Calibration of Acoustic Doppler Current Profiler Apparent Bedload Velocity to Bedload Transport Rate

“…The parameterization of bed roughness is an additional topic in which high fidelity models can contribute to improve representations at larger scales. Rameshwaran, Naden, and Lawless (2011) and Zeng and Li (2012), for example, have recently demonstrated that three-dimensional RANS simulations perform better with wall models based on a spatially averaged roughness that considers the forminduced momentum due to drag, which can also be included in spatial correlations terms that emerge from the double-average approach presented by Nikora et al (2007). A similar methodology can be applied on vegetated streams, in which the roughness depends on the area obstructed by vegetation and properties of the canopy as explained by Nepf (2012).…”

Potential Application of Mesh-Free SPH Method in Turbulent River Flows

“…The roughness reduces velocity near the bed to produce a velocity gradient, and this effect can be transferred to the upper layers of the flow by the turbulent shear stress. According to the summary presented in Table 1, the drag force method coupled with a suitable turbulence model has been shown to be an appropriate way of modelling the roughness effect in grid-based methods [29,33,34], which can be also applied in mesh-free particle methods. Ideally, the production of near-wall velocity gradient can be modelled by an appropriate drag force model and the transportation of shear to upper layers can be modelled by a suitable turbulence model.…”

“…3) and below this level l m is assumed to be zero. However, in some other studies, the distribution of mixing length in the interfacial sub-layer is assumed in a different way (For instance see [34]). In the present work, the zero-reference of the mixing length has been found by using numerical trials so as to achieve the best fit of mean velocity profile to the measured data.…”

SPH modelling of depth‐limited turbulent open channel flows over rough boundaries

“…Wiberg and Smith divided the total shear stress into a fluid shear component and a form‐induced component and used a mixing‐length model for the former and a drag force equation for the latter to calculate the velocity distributions in a steep stream over coarse gravel beds. Besides these, Cui et al , Carney et al and Zeng and Li are some other examples of studies in which the drag concept has been applied to model the effect of wall roughness on the flow. Among them, Zeng and Li used a wall function approach to treat the shear boundary for small‐scale rough bed elements and a drag force model for large‐scale rough beds when the wall function approach was unable to reproduce the correct velocity distributions.…”

“…Besides these, Cui et al , Carney et al and Zeng and Li are some other examples of studies in which the drag concept has been applied to model the effect of wall roughness on the flow. Among them, Zeng and Li used a wall function approach to treat the shear boundary for small‐scale rough bed elements and a drag force model for large‐scale rough beds when the wall function approach was unable to reproduce the correct velocity distributions.…”