https://cyberleninka.org/article/n/1387160.pdf

A LES-based Eulerian–Lagrangian approach to predict the dynamics of bubble plumes

The method of large-eddy simulation (LES) is used increasingly to address research and engineering problems of modern hydraulics. LES simulates directly the large-scale motion of the flow and employs a model to account for the effects that small-scale turbulence imposes on large eddies. This paper summarizes recent hydraulic and hydro-environmental research in which LES has been used. It demonstrates a wide range of applicability of the method and highlights some important research contributions that have been made in studies of large-scale turbulence-dominated flows in which LES delivered accurate predictions. Despite its recent successes, LES is not yet considered to be a universal tool in hydraulics; it cannot (yet) simulate certain flows of hydraulic interest, either because of lack of adequate supergrid models to handle utterly complex flow physics or because current computing resources hinder its applicability to real-life flows at realistically high Reynolds numbers. The paper discusses the...

Large-eddy simulation in hydraulics: Quo Vadis?

An immersed boundary-based large-eddy simulation approach to predict the performance of vertical axis tidal turbines

Hydrodynamic loadings on a horizontal axis tidal turbine prototype

The paper examines the problem of prediction of uniform turbulent flow in a compound channel with the nonlinear k‐e model. This model is capable of predicting the secondary currents, caused by the anisotropy of normal turbulent stresses, that are important features of the flow in compound channels, as they determine the transverse momentum transfer. The model is applied to reproduce experimental runs available in the literature. The comparison shows that the model predicts with accuracy the distribution of the primary velocity component, the secondary circulation, and the discharge distribution. The numerical results are used to search a subdivision surface between main channel and floodplain on the basis of the flow field and to compare different subdivision surfaces on the basis of the discharge distribution by a simple uniform flow formula. The better subdivision surfaces as predicted by the model are the diagonal surface going from the corner between main channel and floodplain to the free surface on ...

Closure of "Velocity Distribution in Compound Channel Flows by Numerical Modeling"

Two separate large eddy simulations (LES) are carried out to investigate the effects of accurate computation of the curvilinear water-surface deformation of the flow through a bridge contraction. One LES employs the rigid-lid boundary condition at the water surface, while the other uses a highly accurate level-set method (LSM), which allows the water surface to adjust itself freely in response to the flow. The simulation with the LSM is validated with data from complementary physical model tests under analogous geometrical and flow conditions. Streamwise velocity, bed-shear stress and second-order turbulence statistics obtained from both simulations are compared, and it is shown that the turbulence structure of this flow is influenced strongly by the water-surface deformation. While bed-shear stresses and first-order statistics are very similar for both cases, the instantaneous turbulence structure and consequently, the second-order statistics, are distinctly different. The correct prediction of the water-surface deformation of such flows is deemed important for the accuracy of their simulation.


Read More: http://ascelibrary.org/doi/10.1061/%28ASCE%29HY.1943-7900.0001028

Free-Surface versus Rigid-Lid LES Computations for Bridge-Abutment Flow

The results of large eddy simulations (LESs) of turbulent flow in a compound open channel with deep and shallow flood plain depths are presented. These LESs are validated with experimental data, resulting in a good agreement between measured and calculated data. The floodplain-depth-to-main-channel-depth ratio is an important parameter affecting first- and second-order turbulence statistics. The streamwise momentum balance is analysed with respect to the momentum transfer at the interface between the main channel and the floodplain. Depth-averaging of the streamwise momentum equation reveals the dominance of turbulent shear stress terms in the main channel and of secondary currents in the floodplain. Comparisons of the LES results with an analytical solution of the depth-averaged streamwise momentum equation that demonstrate the importance of case-specific calibration of the parameters of the analytical solution. The turbulence anisotropy is quantified and its role in generating secondary currents is illu...

Turbulence statistics in compound channels with deep and shallow overbank flows

This paper reports the results of detailed numerical simulations of the flow over a submerged bridge The method of Large Eddy Simulation (LES) is applied, which allows elucidation of the instantaneous flow and accurate quantification of its turbulence statistics The in-house LES code employs a free surface algorithm based on the Level Set Method (LSM) to determine the complex water surface profile over the bridge, which is validated with data from a physical model of the bridge under analogous flow conditions Numerically predicted water surface profiles show good agreement with measured data The water surface resembles that of the flow over a broad-crested weir with a plunging nappe and a standing wave downstream of the bridge The mean flow is characterized by a multitude of complex flow features including horizontal recirculation zones upstream and downstream of the bridge abutment and vertical recirculation zones of the separated plunging flow The latter influences significantly the near-b

Flow dynamics through a submerged bridge opening with overtopping

Large Eddy Simulations (LES) are performed for an open channel flow over a mildly sloped pool-riffle sequence that had been investigated experimentally at the Ven Te Chow hydrosystems laboratory at the University of Illinois at Urbana-Champaign. A train of low-angled ( 7.2° ) bedforms were placed in a 60cm wide rectangular flume at a water-depth-to-bedform-height of H/k ≈ 1 . The Reynolds number Re , based on the bulk velocity U(bulk) and the maximum flow depth H, is approximately Re=20,000 . Measured velocities are used to validate the simulations at selected verticals along the center-line of the flume. The code HYDRO3D is used to solve the filtered Navier Stokes equations on a curvili-near non-uniform grid. Overall, good agreement between measured and computed quantities is found. A shear layer forms in the decelerating part of the pool-riffle sequence and alters turbulence intensities con-siderably. The instantaneous flow field is investigated with emphasis on the occurrence of turbulence structures. Keywords:

Sibel Kara

Papers

Free-Surface versus Rigid-Lid LES Computations for Bridge-Abutment Flow

Turbulence statistics in compound channels with deep and shallow overbank flows

Flow dynamics through a submerged bridge opening with overtopping

Turbulent flow over a mildly sloped pool-riffle sequence

Water surface response to flow through bridge openings