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The objective of the study is to use a 3D Acoustic Doppler Velocimeter (ADV) to gauge the typical flow and turbulence characteristics within a non-uniform open channel. The findings of experimental examinations of the subcritical flow along the channel are presented in this work. The behavior of sand grains in turbulent open channel flow across porous and rough bed surfaces was examined in laboratory research, and the results were obtained. The properties of turbulent flow, i.e., turbulence intensity, turbulent kinetic energy, and Reynolds shear stresses, are determined from ADV data. The continuity equation and the Reynolds equation of open-channel flow have been used to build theoretical formulations for the velocity distribution and Reynolds stress distribution in the vertical direction. Measured profiles of vertical velocity and Reynolds stress are compared to the derived expressions. The impact of the size of particles on the distribution of mean flow characteristics is discussed. This work provides a novel origin for the profile and analyzes the behavior of the vertical velocity distribution in the region where fully formed turbulence is dominating in open channels using the Navier–Stokes equations. In comparison to other sand roughness, Chopan sand bed (with greater density) exhibits the strongest turbulence intensities in both vertical and streamwise direction just next to the bed when away from the channel boundary. In contrast to flow across a rough surface, the variance ranges between 150 and 250% concerning the channel bed's roughness type, impacting the velocity triple products that signifies transfer of turbulent kinetic energy. [ABSTRACT FROM AUTHOR]

This work proposes the use of an array of yawed porous vanes to control the lateral bedload transport by locally steering bedform migration and maximize the amount of sediments redirected toward a potential sediment extraction system or bypass channel. A laboratory experiment was conducted in a quasifield-scale channel with an array of permeable vanes installed on one side, in live-bed conditions under bedload dominant regime, i.e., negligible suspended load. A baseline experiment without vanes was also performed for comparison. The evolution of migrating bedforms of different scales was tracked in space and time using a high-resolution, state-of-the-art laser scanning device. The bedload transport rate in the streamwise direction was first calculated using bedforms' geometry and migration velocity, and then spatially distributed over the entire monitored area using a new Eulerian-averaged grid-mapping method. This allowed us to introduce a new methodology to estimate the lateral bedload transport using control volume theory and applying mass conservation. Quantitative assessments of lateral bedload transport along the channel yield consistent results, suggesting that the vanes effectively move sediments laterally as intended. Under the investigated setup, the maximum lateral sediment transport rate ranges from 9% to 18% of the whole domain-averaged streamwise transport rate. The developed methodology also allowed to identify the location where sediment capture could be maximized for the given vane spatial distribution. Practical Applications: In river engineering, in-stream structures are used to control flow and sediment movement to prevent erosion, intake clogging, and habitat disruption. Submerged vanes are small, angled structures that are installed to redirect sediments toward a preferred direction by creating secondary flow circulations. This study tests experimentally an array of porous vanes in an open channel to measure and quantify the lateral displacement of sediment. Porous plates were selected to minimize local scour and anchoring requirements while directing flow, bedforms, and sediment laterally. The amount of sand moved laterally is measured by comparing the streamwise bedform transport within and outside of the vane array. The proposed vane array is part of a modular hydrosuction sediment bypass system being developed for low-head dams, which features inlets to collect coarse sediments and siphon them over the dam via a slurry conduit. The vane array is meant to be installed upstream of the collector to increase the lateral transport of coarse sediment toward the intake structures. Porous elements can potentially be replaced by vegetation and log structures for nature-based alternatives. [ABSTRACT FROM AUTHOR]

This study investigates the impact of insufficient spanwise spatial resolution on the measurement accuracy of streamwise velocity fluctuations over rough walls. We use a direct numerical simulation (DNS) database of turbulent open-channel flow over three-dimensional sinusoidal roughness with varied wavelengths and roughness heights. Employing a triple decomposition, we investigate both the attenuation of the turbulent fluctuations (about the local mean), u ′ and the dispersive stresses (roughness-induced fluctuations of the time-averaged mean about the global mean), U ~ . A boxcar filter on DNS data is applied to investigate the effects of spanwise spatial filtering on these quantities. Our analysis reveals the significance of two key length-scale ratios for velocity measurements over rough walls: the wire length relative to the spatially and temporally plane-averaged Kolmogorov scale at the roughness crest ( l / ⟨ η ⟩ k ), and the wire length relative to the roughness spanwise wavelength ( l / Λ y ). We observe that maintaining l / ⟨ η ⟩ k constant while increasing l / Λ y attenuates the variance of U ~ and u ′ within the roughness sublayer. When fixing l / Λ y , an increase in l / ⟨ η ⟩ k influences the turbulent fluctuations across all wall-normal locations. These findings highlight the necessity of considering both length scales when evaluating spanwise spatial resolution in turbulence measurements over rough walls. [ABSTRACT FROM AUTHOR]

Computational models in hydro-environmental engineering are diverse in their background formulation and span from two-dimensional depth-averaged shallow water models, to complex fully three-dimensional turbulence models resolving large-eddy simulation with surface capturing techniques, and to Lagrangian particle-based methods. This paper presents a first-of-its-kind comparison of six different computational hydraulics fluid dynamics models, namely Iber+, HO-SWM, GBVC, OpenFOAM (RANS), Hydro3D (LES) and DualSPHysics (SPH), in the prediction of mean velocities and free-surface dynamics in two benchmarks involving open-channel flows with symmetric lateral cavities. Results show that shallow-water models capture relatively well the main large-scale coherent structures of the in-cavity flow, with wider shear layers compared to three-dimensional models, and higher velocities in the main channel. Three-dimensional RANS, LES and SPH yield improved predictions of mean velocities compared with experimental data. Computational cost has been quantified for all models with a logarithmic growth when increasing model complexity. The transverse standing wave is captured by most models, with the shallow-water ones matching the theoretical value, while the three-dimensional models overestimate it slightly. [ABSTRACT FROM AUTHOR]

This document is a discussion of various research papers on different topics. The first paper explores the influence of downstream channel width on flow features in a T-shaped open-channel confluence. The authors conducted numerical simulations to study flow characteristics such as stagnation zone location, tributary inflow angles, separation zone dimensions, flow acceleration, secondary flow patterns, and bed shear stresses. The second paper focuses on the backwater effect in a T-shaped junction channel, examining the impact of junction angle, width ratio, discharge ratio, and bed level discordance. The third paper discusses the backwater effect in river channels caused by variations in bed level and width ratios, finding that increasing discharge upstream and enlarging the downstream width of the main channel can mitigate the backwater effect. The final report analyzes the properties of the star system GJJ211936, including its spectral type, luminosity, and distance from Earth. It also examines the potential habitability of the system's exoplanets and emphasizes the importance of further research in the search for extraterrestrial life. [Extracted from the article]

Zero-plane is an important reference level included in the logarithmic velocity profile. The prediction of the zero-plane displacement remains challenging, especially in open-channel flows with submerged vegetation. In this study, we first review the existing formulas for estimating the zero-plane displacement. Then, we conducted a series of laboratory experiments of open-channel flows with submerged rigid vegetation, by varying flow rate, water depth, vegetation density, and stem diameter. By utilizing particle image velocimetry (PIV) technique, the spatio-temporal averaged (double-averaged) flow velocity and Reynolds shear stress profiles were obtained. The data analysis shows that the zero-plane displacement is almost proportional to the surface layer depth for the shallow flow cases. As the flow depth increases, the zero-plane displacement tends to be constant and increases with decreasing vegetation density. This result substantiates the hypothesis that the zero-plane displacement is related to large-scale eddies. Lastly, a heuristic model is developed to explain possible variations of the large-scale eddies, which yields a formula for predicting the zero-plane displacement for flows subjected to submerged rigid vegetation. [ABSTRACT FROM AUTHOR]

The commercial CFD package Fluent and the Reynolds stress model were used to simulate the hydraulic characteristics with three types of vegetation distribution: longitudinal, interlaced and patch. Each type was aggregated to the middle line l of the water flow in an equal proportion of 0.5, resulting in a total of nine landscape vegetation arrangements. The numerical model was verified and showed a high level of consistency with the experimental comparison; the results indicate the following: (1) As the distribution of landscape vegetation on both sides becomes increasingly concentrated from a loose state to the middle line l of the flow, the flow velocity declines and the maximum Reynolds stress rises, and the greater the Reynolds stress, the more powerful the shear layer, contributing to turbulence, generating mass and momentum exchange and enhancing the vertical transport of momentum. (2) Compared with the gap area, the flow velocity in the vegetation area is smaller, the turbulent kinetic energy is larger and the maximum Reynolds stress of the bottom flow is larger; the larger sediment particles tend to deposit in the gap area, while smaller sediments tend to deposit in the vegetation area. At the same time, the vegetation area is more prone to deposits than the gap area. (3) Under the same vegetation density, whether in the test area or the wake area, the water blocking capacity and the deposition capacity are in the following order: patch distribution pattern > interlaced distribution pattern > longitudinal distribution pattern. [ABSTRACT FROM AUTHOR]

The drainage systems of tunnels situated in limestone regions frequently encounter crystallization blockages. Numerous studies have addressed this issue, and their findings identified factors such as the flow velocity and temperature as influencing the crystallization process. However, these studies could not predict the occurrence of crystallization. Regarding theoretical approaches, most studies have focused on full-pipe operations or have solely considered flow-field dynamics without including simulations of the chemical reactions and mass transfers. This study introduces a mass-transfer model for drainage pipes based on a two-phase flow (water and air) with a free surface and non-full pipe flow that simulates the crystallization deposition process in drainage pipes. This model can predict the deposition conditions at varying flow velocities and intuitively visualize the crystallization process under the influence of various factors. The impact of flow velocity on the overall crystallization deposition process can be directly analyzed through simulations developed using this model. The results show that under conditions of incomplete pipe flow with no pressure at the outlet, the weight of the deposition first increases and then decreases within a certain velocity. This model can depict the variations within a 30 d period. [ABSTRACT FROM AUTHOR]

The primary objective of this study was to investigate the vertical distribution of streamwise velocity in open-channel flow carrying sediments. The governing equations encompassing mass and momentum balances for the fluid are employed, with the Reynolds stress term linked to the mixing length of the flow, which is treated as a function of concentration. Both wall-normal and settling velocities are considered as functions of concentration. Notably, a concentration-dependent von Kármán constant, incorporating the effect of suspended sediment particles, is utilized in the mixing length expression, rendering the model more realistic. The resultant nonlinear ordinary differential equations are solved numerically. The model was analyzed for particle-free flow, wherein the concentration term was set to zero. The deviation of the velocity profile in this scenario from the original scenario with concentration underscores the significance of incorporating the concentration term in the study of velocity models in sediment-laden flows. Additionally, the developed velocity model was validated against pertinent experimental data available in the literature. Subsequent error analysis was conducted to compare the model with experimental data. [ABSTRACT FROM AUTHOR]

The study delves into the impact of degassing on bubble populations in air-entraining flows, highlighting the dominance of degassing over fragmentation in balancing entrainment. Through theoretical models and computational simulations, researchers identified a split power law for bubble size distribution in turbulence-driven and buoyancy-driven regimes. The findings shed light on bubble dynamics in multiphase flows, offering insights into various aspects such as bubble breakup, fragmentation by small eddies, and the effect of nonlinear drag on bubble rise velocity. [Extracted from the article]

Two-dimensional free-surface flow over localised topography is examined, with the emphasis on the stability of hydraulic-fall solutions. A Gaussian topography profile is assumed with a positive or negative amplitude modelling a bump or a dip, respectively. Steady hydraulic-fall solutions to the full incompressible, irrotational Euler equations are computed, and their linear and nonlinear stability is analysed by computing eigenspectra of the pertinent linearised operator and by solving an initial value problem. The computations are carried out numerically using a specially developed computational framework based on the finite-element method. The Hamiltonian structure of the problem is demonstrated, and stability is determined by computing eigenspectra of the pertinent linearised operator. It is found that a hydraulic-fall flow over a bump is spectrally stable. The corresponding flow over a dip is found to be linearly unstable. In the latter case, time-dependent simulations show that ultimately, the flow settles into a time-periodic motion that corresponds to an invariant solution in an appropriately defined phase space. Physically, the solution consists of a localised large-amplitude wave that pulsates above the dip while simultaneously emitting nonlinear cnoidal waves in the upstream direction and multi-harmonic linear waves in the downstream direction. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to identify the behaviour of neutrally buoyant microplastics (specific density, 0.94) in different hydrodynamic conditions while focusing on combined wave–current conditions and the mixing across the hyporheic zone. For in-water-column microplastics, it was observed that the streamwise dispersion of neutrally buoyant microplastics is comparable to solute dye in both slow open-channel flow conditions and combined wave–current conditions. However, for in-bed microplastics, when compared to soluble tracers, the longer timespans associated with the hyporheic exchange process allowed the density effects to enhance the vertical exchange when compared to solutes. [ABSTRACT FROM AUTHOR]

Tsunamis, though infrequent, wield devastating power on coastal regions, necessitating accurate simulation techniques to comprehend their impact and enhance disaster preparedness. Despite significant advances in modern computational fluid dynamics, these simulations continue to pose considerable challenges, including numerical intricacies and substantial computational costs. Owing to its remarkable computational efficiency and high performance, the lattice Boltzmann method (LBM) is being increasingly used for simulating large-scale tsunamis. This review paper systematically surveys the application of the free-surface flow model using the LBM to simulate tsunamis, covering its theoretical underpinnings, numerical implementation, and validation against real-world events. Furthermore, the paper discusses challenges, limitations, and ongoing developments in the application of the LBM for tsunami simulations, elucidating avenues for future research. By amalgamating insights from diverse studies, this review underscores the role of the LBM as a tool for advancing our understanding of tsunamis and increasing coastal resilience. HIGHLIGHTS: Lattice Boltzmann method investigated for tsunami simulations Challenges, limitations, and ongoing developments in tsunami simulation discussed Systematical survey of the application of the free-surface flow model Theoretical underpinning, numerical implementation, and real-world validation [ABSTRACT FROM AUTHOR]

Spur dikes are deployed to regulate the flow in an open channel for navigation and bank protection as well as protection of beaches against erosion. The spacing between spurs is a crucial design parameter. The reattachment length at the lee side of a single spur dike may be viewed as the maximum spacing between consecutive spurs, as a larger spacing may result in propagation of the recirculation flow toward the bank between them. This paper presents a physically based approach to characterize and compute the reattachment length in the lee side of a vertical spur dike under both fixed and mobile beds. A new model is introduced based on the principles of momentum and energy. The reattachment length is inversely proportional to the scour depth, resulting in approximately a 4%‒38% reduction when reaching the equilibrium scour compared to no scour condition, and the relative reattachment length ranges from 8.5 to 13.5b for the scoured bed. The model is applied to the field data, and the predicted reattachment length is compared with the spacing between two consecutive spurs. This formula performs better in estimating the reattachment length than other reported formulas. It proves useful for hydraulic engineers to decide the efficient design spacing between spurs during bank protection and navigation channel regulation design. [ABSTRACT FROM AUTHOR]

An understanding of turbulence and mixing is essential to the knowledge of turbulent dissipation, sediment transport, advection of nutrient-rich and organic effluents, and stormwater runoff in prototype water systems, as well as in laboratory channels used for physical modeling of geometrically-scaled full-scale water bodies and for validation of computational models. The acoustic Doppler velocimeter (ADV) system is a robust instrument well suited for such turbulence measurements in open channel flows. The application of acoustic Doppler velocimeter to transient free-surface flows is reviewed in this paper. Based upon field applications and laboratory experiments, the intricacy and inherent difficulties are discussed. The experience and expertise in transient flows highlighted the importance of the signal processing and precise synchronization. Finally, we stress a major benefit of the acoustic Doppler velocimetry for its capability to be used in both field and laboratory, in turn providing some level of confidence in the comparison between full-scale and laboratory data. [ABSTRACT FROM AUTHOR]

Understanding the ecological conditions of vegetation growth in water sources is vital to appraise the influence of vegetation on river engineering. Based on the experimental information that is accessible, the consequences of vegetation on flow resistance is described as an alteration in the drag coefficient and the planned area. The current study analytically estimates the vertical distribution of stream-wise velocity in open-channel flow while considering rigid and flexible vegetation. The flow is vertically separated into top free water layer and bottom vegetation layer using the projected deflection height of both vegetation. Related momentum calculations for each layer are then derived. Based on the gathered experimental data, a 3D numerical model with various simulation situations is used to model, calibrate, and evaluate the artificial cylinders. A considerable deflection analysis is utilised to calculate the velocity-dependent stem height. This has proven to be more precise compared to formerly deflection investigation. The estimated outcomes show that precise predictions may be made for the vertical contours of vertical Reynolds shear stress based on mean horizontal velocity. The numerical simulations demonstrate that plant flexibility reduces the vertical Reynolds shear stress and prompted flow resistance force of the vegetation. [ABSTRACT FROM AUTHOR]

In this article, the performances of the SPH method to solve Shallow Water Equations SWEs with three investigation parameters were studied, such as the type of kernel functions, namely: cubic spline, Gaussian and quintic spline kernels, the number of particles used and the stabilization terms injected, specifically: Lax Friedrichs flux, artificial viscosity and two shocks Riemann solver. Three benchmarking tests make the subject of unsteady free surface flow in this study. It is 1D typical dam-break on wet and dry bottom; 2D partial dam-break on a dry floodplain and 2D partial dam-break on channel with 90° bend. The analysis of the different errors between the numerical and analytical solutions and/or the experimental data shows that the SPH method gives reliable values with the selected optimal parameters which are the cubic kernel function and the artificial viscosity term. The increase in the number of particles increases the precision but also the calculation time. [ABSTRACT FROM AUTHOR]

The present paper focuses on the investigation of the turbulent characteristics of an open-channel flow by employing the micropolar model. The underlying model has already been proven to correctly describe the secondary phase of turbulent wall-bounded flows. The open-channel case comprises an ideal candidate to further test the micropolar model as many environmental flows carry a secondary phase, the behavior of which is of great interest for applications such as sedimentation transport and debris flow. Direct Numerical Simulations (DNSs) have been carried out on an open channel for R e b = 11,200 based on mean crossectional velocity, channel height, and the fluid kinematic viscosity. The simulated results are compared against previous experimental as well as Langrangian DNS data of similar flows, with excellent agreement. The micropolar model is capable of describing the same problem but in an Eulerian frame, thus significantly simplifying the computational cost and complexity. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to identify the behaviour of neutrally buoyant microplastics (specific density, 0.94) in different hydrodynamic conditions while focusing on combined wave–current conditions and the mixing across the hyporheic zone. For in-water-column microplastics, it was observed that the streamwise dispersion of neutrally buoyant microplastics is comparable to solute dye in both slow open-channel flow conditions and combined wave–current conditions. However, for in-bed microplastics, when compared to soluble tracers, the longer timespans associated with the hyporheic exchange process allowed the density effects to enhance the vertical exchange when compared to solutes.

Understanding the ecological conditions of vegetation growth in water sources is vital to appraise the influence of vegetation on river engineering. Based on the experimental information that is accessible, the consequences of vegetation on flow resistance is described as an alteration in the drag coefficient and the planned area. The current study analytically estimates the vertical distribution of stream-wise velocity in open-channel flow while considering rigid and flexible vegetation. The flow is vertically separated into top free water layer and bottom vegetation layer using the projected deflection height of both vegetation. Related momentum calculations for each layer are then derived. Based on the gathered experimental data, a 3D numerical model with various simulation situations is used to model, calibrate, and evaluate the artificial cylinders. A considerable deflection analysis is utilised to calculate the velocity-dependent stem height. This has proven to be more precise compared to formerly deflection investigation. The estimated outcomes show that precise predictions may be made for the vertical contours of vertical Reynolds shear stress based on mean horizontal velocity. The numerical simulations demonstrate that plant flexibility reduces the vertical Reynolds shear stress and prompted flow resistance force of the vegetation.

This paper investigates the impact of flood-induced hydrodynamic forces and high discharge on the masonry arch "Hannibal Bridge" (called "Ponte di Annibale" in Italy) using the Hydraulic Engineering Center's River Analysis Simulation (HEC-RAS) v6.5.0. hydraulic numerical method, incorporating Unmanned Aerial Vehicle (UAV) photogrammetry and aerial Light Detection and Ranging (LIDAR) data for visual analysis. The research highlights the highly transient behavior of fast flood flows, particularly when carrying debris, and their effect on bridge superstructures. Utilizing a Digital Elevation Model to extract cross-sectional and elevation data, the research examined 23 profiles over 800 m of the river. The results indicate that the maximum allowable water depth in front of the bridge is 4.73 m, with a Manning's coefficient of 0.03 and a longitudinal slope of 9 m per kilometer. Therefore, a novel method to identify the risks through HEC-RAS modeling significantly improves the conservation of masonry bridges by providing precise topographical and hydrological data for accurate simulations. Moreover, the detailed information obtained from LIDAR and UAV photogrammetry about the bridge's materials and structures can be incorporated into the conservation models. This comprehensive approach ensures that preservation efforts are not only addressing the immediate hydrodynamic threats but are also informed by a thorough understanding of the bridge's structural and material conditions. Understanding rating curves is essential for water management and flood forecasting, with the study confirming a Manning roughness coefficient of 0.03 as suitable for smooth open-channel flows and emphasizing the importance of geomorphological conditions in hydraulic simulation. [ABSTRACT FROM AUTHOR]

High Froude-number open-channel flows can entrain significant volumes of air, a phenomenon that occurs continuously in spillways, in free-falling jets and in hydraulic jumps, or as localized events, notably at the toe of hydraulic jumps or in plunging jets. Within these flows, turbulence generates millions of bubbles and droplets as well as highly distorted wavy air–water interfaces. This phenomenon is crucial from a design perspective, as it influences the behaviour of high-velocity flows, potentially impairing the safety of dam operations. This review examines recent scientific and engineering progress, highlighting foundational studies and emerging developments. Notable advances have been achieved in the past decades through improved sampling of flows and the development of physics-based models. Current challenges are also identified for instrumentation, numerical modelling and (up)scaling that hinder the formulation of fundamental theories, which are instrumental for improving predictive models, able to offer robust support for the design of large hydraulic structures at prototype scale. [ABSTRACT FROM AUTHOR]

This paper concerns a numerical stabilization method for free-surface ice flow called the free-surface stabilization algorithm (FSSA). In the current study, the FSSA is implemented into the numerical ice-flow software Elmer/Ice and tested on synthetic two-dimensional (2D) glaciers, as well as on the real-world glacier of Midtre Lovénbreen, Svalbard. For the synthetic 2D cases it is found that the FSSA method increases the largest stable time-step size at least by a factor of 5 for the case of a gently sloping ice surface (∼ 3°) and by at least a factor of 2 for cases of moderately to steeply inclined surfaces (∼ 6° to 12°) on a fine mesh. Compared with other means of stabilization, the FSSA is the only one in this study that increases largest stable time-step sizes when used alone. Furthermore, the FSSA method increases the overall accuracy for all surface slopes. The largest stable time-step size is found to be smallest for the case of a low sloping surface, despite having overall smaller velocities. For an Arctic-type glacier, Midtre Lovénbreen, the FSSA method doubles the largest stable time-step size; however, the accuracy is in this case slightly lowered in the deeper parts of the glacier, while it increases near edges. The implication is that the non-FSSA method might be more accurate at predicting glacier thinning, while the FSSA method is more suitable for predicting future glacier extent. A possible application of the larger time-step sizes allowed for by the FSSA is for spin-up simulations, where relatively fast-changing climate data can be incorporated on short timescales, while the slow-changing velocity field is updated over larger timescales. [ABSTRACT FROM AUTHOR]

Two-dimensional free-surface flow past a submerged rectangular disturbance in an open channel is considered. The forced Korteweg–de Vries model of Binder et al. (Theor Comput Fluid Dyn 20:125–144, 2006) is modified to examine the effect of varying obstacle length and height on the response of the free-surface. For a given obstacle height and flow rate in the subcritical flow regime an analysis of the steady solutions in the phase plane of the problem determines a countably infinite set of discrete obstacle lengths for which there are no waves downstream of the obstacle. A rich structure of nonlinear behaviour is also found as the height of the obstacle approaches critical values in the steady problem. The stability of the steady solutions is investigated numerically in the time-dependent problem with a pseudospectral method. [ABSTRACT FROM AUTHOR]

This study proposes the foremost application of the entropy concept to investigate the streamwise S-type mean velocity distribution with infection-phenomenon in turbulent open-channel flows and turbulent Couette flows. Probability based fractional entropy is used for this study. Using the concept of entropy maximization the velocity distribution models are derived. Proposed models are fully analytical and applicable to the whole flow depth in both for open-channel flows and the turbulent Couette flows. All the proposed models are validated with different experimental data sets, field data and DNS data available in the literature. The validation results show good performance for both of the velocity distribution models. Apart form validation, the present velocity distribution models are compared with deterministic (non-entropy based) models since there exists no entropy based velocity distributions to describe the infection-phenomenon in turbulent open-channel flows and turbulent Couette flows. To understand the performance of these models, the relative error and the coefficient of determination ( R 2 ) are computed. Results of the error analysis show the good efficiency of the proposed models for several experimental and field data sets. [ABSTRACT FROM AUTHOR]

This study investigates turbulent open-channel flows over beds of irregularly arranged particles, using direct numerical simulations at a friction Reynolds number of R e τ = 300. Two distinct cases are examined: a polydisperse bed (P800) composed of multiple layers of randomly distributed spheres of varying sizes, and a monodisperse bed (M1015) formed by a random distribution of uniform sized spheres, with a bottommost single layer of varied-sized particles to introduce realistic randomness. Our investigation unveils a rich network of low- and high-speed streaks within the flow field, exhibiting distinctive behaviors in different bed configurations. The P800 case presents a poorly organized flow pattern induced by the varied particle sizes and arrangements, while the M1015 case shows a more regular flow pattern, marked by larger streaks. We also observe that total wall shear stress is substantially influenced by surface roughness-induced drag, extending beyond the effects documented in existing studies of open-channel flows. The present study reveals intricate secondary flow patterns over irregular particle beds. Large-scale circulations are discerned around particle crests in the P800 case and localized circulations with increased turbulence in the M1015 case. Furthermore, analysis of Reynolds stress tensor components indicates that roughness disrupts coherent turbulent eddies, consequently mitigating peak stress. We quantify correlations between drag force and local fluid velocity fluctuations. Notably, a larger deviation in drag is observed in the P800 case compared to M1015, accentuating the influence of particle size and distribution on fluid–particle interactions. [ABSTRACT FROM AUTHOR]

In nature and engineering, fluid movements involving swirling patterns, or vortices, are common occurrences. Some flows involve free-surface vortices that can potentially lead to a phenomenon termed gas entrainment (GE). There is no validated tool that can predict the free-surface profile of the gas core prior and subsequent to the GE. This study focuses on experimental and numerical investigation of flows with unsteady free-surface vortices that can potentially lead to gas entrainment. An extensive experimental work, performed in a dedicated experimental setup built in the present study, yields two main contributions. First, a new GE onset criterion, based on implementing dimensional analysis to the experimental results, is developed. The onset criterion is found to be suitable also for other experiments in the literature. Second, the experimental acquisition of the free-surface profiles, obtained with a high-speed camera, is used for validating the numerical approach. This three-dimensional numerical tool incorporates Large Eddy Simulation to capture turbulence, with Volume-of-Fluid approach to simulate free-surface profiles. The model predicts with high accuracy the free-surface profiles in cases with and without GE, observed experimentally. Then, the detailed simulation results for this type of flows are analyzed quantitatively for the first time in the available literature, using radial, axial, and tangential velocity components. The present study sheds new light on free-surface vortex flows, in general. The experimental and numerical achievements in this study can serve as a tool both to predict the free-surface flow profiles with high accuracy and to prevent gas entrainment in the engineering systems. [ABSTRACT FROM AUTHOR]

In the gravity-driven free-surface flow of grains, the mechanism of the segregation phenomenon in binary granular flow is mainly attributed to kinetic sieving and squeeze expulsion. Although much literature has delved into the penetration of small grains through random fluctuation sieving, independent research on the microscopic mechanism of squeeze expulsion remains insufficient. Our previous research found that squeeze expulsion is particularly prominent in quasi-two-dimensional binary disk grain flow. Based on this result, we used the discrete element method (DEM) and experiments to explore the mechanism of squeeze expulsion. The results show that the anisotropy of the contact force chain network and the velocity difference of the grains in different positions play a key role in the expulsion behavior of the grains. This expulsion behavior is influenced by the dynamics and instability of the force chains, manifesting itself as a probabilistic phenomenon. Through DEM simulations, we quantified the probabilities of large grains being expelled at different positions and under various slope angles. It was found that as the slope angle increases, the probability of large grains being expelled to the upper layer also increases, intensifying granular segregation. The probability of large grains being expelled is highest in the granular flow substrate layer. The revealed mechanism of squeeze expulsion in this study is crucial for understanding grain mixing and separation. [ABSTRACT FROM AUTHOR]

Time-averaged velocity fields in uniform open-channel flows over rough beds may exhibit spatial heterogeneities due to the effects of bed roughness and secondary currents (SCs). The latter typically originate from the turbulence anisotropy and spatial heterogeneity introduced by the solid and mixed corners (i.e., between sidewalls and water surface), but may also appear due to roughness spanwise heterogeneities, e.g., associated with patchy vegetation distributions or streamwise sediment ridges on the channel bed. In this paper, we propose rigorous conservation equations for momentum, kinetic energy and fluid stresses accounting for the contributions of bed roughness and SCs, separately. Particular attention is given to the terms regulating the energy exchanges between roughness-induced and SC-related motions, which are expected to provide information on the physical mechanisms leading to the generation of roughness-induced SCs. The proposed approach is illustrated using a large-eddy simulation of a rough-bed open-channel flow. Article Highlights: A new set of double-averaged equations separating dispersive fluctuations due to bed roughness and secondary currents is presented. The proposed equations describe conservation of momentum, kinetic energy and fluid stresses. The equations are illustrated using a large-eddy simulation data set. [ABSTRACT FROM AUTHOR]

Lateral cavities are a popular object of study in hydraulic research as they are widely found in rivers and hydraulic facilities and significantly impact flow patterns, sediment transport, and water quality in aquatic ecosystems. While the effects of open-channel cavities on various aspects including characteristics of three-dimensional structures have been extensively studied, the role of vertical flow structures in the cavity has not been focused on. This study examines the relationship between the shallowness parameter and the three-dimensional flow effects on the dynamics of an open-channel lateral cavity flow with horizontal vortex motion, comparing the conventional two-dimensional model (2DC), advanced depth-integrated models including general bottom velocity calculation method (GBVC) with the ability to consider vertical flow structures, simplified bottom velocity calculation method with the shallow water assumption (SBVC), a three-dimensional model (3DC), and experimental data. The comparison results demonstrate that the three-dimensional flow effect significantly impacts the velocity distribution and vortex evolution in the cavity. The GBVC model demonstrates a good agreement with the flow patterns by the 3DC model and experimental results in the cavity, whereas the 2DC and SBVC models are unsuitable for deep-water conditions. [ABSTRACT FROM AUTHOR]

Standing flows in natural channels often cause phenomena that can be very serious, such as flooding, deformation of channel geometry, and destruction of infrastructure (dams, bridges, and culverts). This study focuses on the computation of gradually varying permanent flows (backwater curves) by two methods: direct integration (Chow) and successive approximation (depth variation). To solve the system of equations governing the problem of gradually varying one-dimensional stationary flows at a free surface, a large amount of data should be taken into account, namely, the flow rate, the water head, the mean flow velocity, the rugosity, and the slope. These parameters are very important, as they cause nonlinear behavior, making the problem and its mathematical solution complex. Digitizing these parameters can help to determine and visualize the longitudinal profile of the water line for known flow rates. This study aimed to: (1) determine the influence of rugosity on gradually varying steady flows and the overclassification of eddy curves in a prismatic channel, (2) study the effect of geometric shape on these flows, and (3) investigate and compare the effects of the calculation methods. The results reveal the great influence of rugosity on gradually varying permanent flows for four selected geometric shapes of the channel, as it has a direct influence on the normal depth and the critical slope. Each time the resistance of the bottom to the flow increases, these results increase. The influence of the geometric shape on these flows is less significant. The comparative study showed a difference between the results obtained. [ABSTRACT FROM AUTHOR]

The primary focus of this work is the coupling of dispersive free-surface flow models through the utilization of a thick interface coupling technique. The initial step involves introducing a comprehensive framework applicable to various dispersive models, demonstrating that classical weakly dispersive models are encompassed within this framework. Next, a thick interface coupling technique, well-established in hyperbolic framework, is applied. This technique enables the formulation of unified models across different subdomains, each corresponding to a specific dispersive model. The unified model preserves the conservation of mechanical energy, provided it holds for each initial dispersive model. We propose a numerical scheme that preserve the projection structure at the discrete level and as a consequence is entropy-satisfying when the continuous model conserve the mechanical energy. We perform a deep numerical analysis of the waves reflected by the interface. Finally, we illustrate the usefulness of the method with two applications known to pose problems for dispersive models, namely the imposition of a time signal as a boundary condition or the imposition of a transparent boundary condition, and wave propagation over a discontinuous bathymetry. [ABSTRACT FROM AUTHOR]

The adoption of baffles is relatively common in the construction of culverts, to assist with the upstream passage of migrating fish species. However, there still is a lack of systematic studies of the complicated hydraulic conditions induced by the baffles to optimize the designs. Herein, near-full-scale physical modeling was performed, focusing on the oscillation and instability of open-channel flow in a fish-friendly culvert equipped with full-height sidewall baffles. High-resolution measurements of the instantaneous flow velocity were obtained using an acoustic Doppler velocimeter. The physical results were marked by the existence of some low-frequency oscillations. A triple decomposition technique was applied to the free-surface and velocity time series. The low-pass components confirmed a unique flow structure, consisting of a high-velocity zone in the main channel and a low-velocity flow reversal within the lateral cavities. The band-pass components corresponded to the low-frequency flow oscillations, highlighting the complicated transverse interactions between the lateral cavity and the main channel. The high-pass velocity components were related to the true turbulence characteristics. This study provides a quantitative data set in support of the sustainable design of culverts to assist with upstream fish migration in artificial and natural fast waterways. [ABSTRACT FROM AUTHOR]

In this paper, we leverage the direct numerical simulation (DNS) data for closed-channel flow for a range of friction Reynolds number (Reτ∼180–5,000) to develop a new one-point friction velocity method (OPFVM) to calculate friction velocity U* in terms of free-surface velocity Um , flow depth h , and kinematic viscosity ν. In contrast to prevalent methods that require several cumbersome near boundary measurements to obtain friction velocity, the OPFVM relies on a single easy-to-measure free-surface velocity measurement. The formulation is used to obtain friction velocity for a closed-channel flow (CCF) DNS regime with Reτ=10,049 and on four open-channel flow (OCF) DNS regimes with Reτ∼180–2,000. The same formulation was then experimentally verified in our laboratory. To avoid being prescriptive, a sensitivity analysis was performed to determine the permissible variation in Um to restrict the error in estimated U* to 2%. The relationship between the depth-averaged velocity Ub and the maximum free-stream velocity Um is also explored using the DNS data sets and an approximate relationship between Ub and Um is proposed. With advances in remote-sensing technology that enables free-stream velocity measurements, this method extends the potential to measure even the friction velocity remotely. Practical Applications: Measuring friction velocity U* is difficult in both laboratory and field settings for engineers and scientists. The proposed new method overcomes this challenge to estimate the friction velocity U* by measuring the velocity Um close to the free surface, flow depth h, and temperature (for viscosity). Because near-surface measurement of velocity is not difficult, this method greatly simplifies the measurement of U* with better accuracy than other prevalent methods in practice. In addition, direct numerical simulation (DNS) data has been used to estimate the average velocity Ub using the measured free-stream velocity Um , which further enables measurement of discharge using a single-point measurement of velocity near the free surface in smooth channels. [ABSTRACT FROM AUTHOR]

Bioroughness plays an important role in modifying the velocity and sediment flux near the riverbed. It is therefore pertinent to study the influence of benthic fauna on the bed forms. To this end, large-eddy simulations are performed to investigate the influence of the arrays of mounds and their density on the turbulence characteristics in an open-channel flow. The simulated distributions of the time-averaged streamwise velocity and the turbulence intensity are in good agreement with the experimental data. Four numerical simulations are performed with varying streamwise spacings of mounds. Details of the time-averaged and instantaneous flow velocities are analyzed by multiple visualization methods, and the effects of the bioroughness density on the equivalent roughness height and the Darcy–Weisbach friction factor are quantified. The time-averaged flow in the wake of the mounds is characterized by a symmetric pair of vortices. The mounds behave like bluff bodies, increasing the riverbed roughness and heterogeneity in the flow environment. An increase in mound density is to promote the development of secondary currents and to increase the dispersive stress near the bed. The peaks of the Reynolds shear stress distributions decrease in both the streamwise and vertical directions for the high-density case due to a blockage effect. The instantaneous flow features, in the form of various turbulence structures, are generated near the top edge and the wake zone of mounds. The spacing between low-speed streaks decreases with an increase in equivalent roughness height. Multifrequency behavior that is observed is a result of shear layer roll-up from the edges of mounds and the flapping of wake. Finally, two formulas for equivalent roughness height and Darcy–Weisbach friction factor are proposed involving the bioroughness density and height. The findings demonstrate the effects of the bioroughness on the near-bed turbulence characteristics and sediment stability. Practical Applications: Bed forms produced by aquatic benthos are usually of small scale but with a large abundance. We performed a flume experiment as well as large-eddy simulations (a high-fidelity numerical simulation approach) to answer whether these microtopographies are important when studying flow and transport processes near the riverbeds. Four numerical simulations are performed with varying mound density. It was found that the microtopographies created by benthos indeed change the near-bed turbulence characteristics and sediment stability. Specifically at high abundances, benthos-induced bed forms could raise the bed roughness and the friction factor eightfold and threefold, respectively. This suggests the necessity of a modified roughness height formula and a friction coefficient formula based on the benthos abundance, which has been carried out in this study. Thus, engineers who are concerned with the flow and sediment transport in habitats of high-abundance benthos (e.g., wetlands and estuaries) may prefer to use these modified formulas and to develop a more accurate model of sediment transport. [ABSTRACT FROM AUTHOR]

The water hammer phenomenon, commonly acknowledged in pressurized pipe-flows is relevant to various water distribution systems. This phenomenon constitutes a major concern for hydraulic researchers and designer, given the dramatic consequences of this phenomenon on hydraulic structures and human life. This study aimed at expanding research on the water hammer waves in the free-surface flow framework. The main objective was to address a comprehensive simulation of the free-surface wave behavior caused by the abrupt closure of sluice-gate in prismatic open channel. The one-dimensional Saint-Venant equations embedding the Boussinesq add-on was used to predict the free-surface wave behavior; which was discretized using the (2–4)-dissipative scheme. Results evidenced the analogy between the water hammer wave behavior in free-surface and pressurized pipe flows. Furthermore, results illustrated that the water hammer maneuver produced a sudden depth rise, about three times of the normal depth value in the cross section adjacent to the gate. From a computational point of view, the proposed solver provided simplicity and accuracy attributes in simulating shock-waves in free-surface-flow. This solver also consumed low computational time compared with the conventional or multiple grid technique – based Finite Element Algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a solution verification and validation study for an overset mesh based numerical wave tank in OPENFOAM, which considers the coupling between a free-surface hydrodynamic flow model, a rigid body motion model, and an overset mesh. The coupling between the rigid body motion solver and the free-surface flow solver was achieved in a segregated manner. Free decay of roll motion of a barge was modeled using the numerical wave tank, and the damping coefficient was selected as the target quantity for solution verification. The least-square based solution verification procedure was adopted, where one of the four types of error estimators was fit to the data in the least-square sense. Both structured and unstructured mesh were tested, and their effects on the convergence order, numerical uncertainty, and error were carefully investigated. From the numerical tests, it is found that the numerical wave tank exhibits a very good convergence property for the floating body problems with structured mesh, i.e., nearly second order in space and first order in time. However, when switching the body-fitted mesh to unstructured mesh, the grid convergence is reduced to first order. Unstructured mesh does not significantly affect the convergence order in time domain, but results in a larger uncertainty due to data scattering. [ABSTRACT FROM AUTHOR]

In natural gravel-bed rivers, fine sediment deposition contributes to the bed morphology and entrapment of plant seeds often leads to the evolution of vegetated areas. Therefore, it is important to understand the transport mechanisms of fine particles between and over large-grain gravels. The present work explores influence of the bursting phenomena on transport of fine grain particles between roughness elements through laboratory experiments. The rough bed consists of hemispherical elements fixed to the flume bed to mimic a natural gravel riverbed. First, two-components of flow velocity within and over the rough bed were measured by particle image velocimetry (PIV) combined with refractive-index matching (RIM). This visualizing method reveals the complex flow structure in a valley of the rough bed; especially, the formation of a horseshoe-shaped vortex at the upstream side of a roughness element. The linear stochastic estimation (LSE) of the conditional velocity field given an upward flow event near the channel bed demonstrates that the horseshoe vortex is temporarily enhanced after a high-momentum flow passes over the roughness crest and a sweep impinges onto the roughness surface. Next, the simultaneous analysis of particle trajectories and flow velocities was performed for some particle entrainment events between roughness elements. Most upward particle motions in the near-bed region are initiated by the upward flow induced by sweep and terminate below the roughness height. On the other hand, some of the particles lifted by sweep are transported beyond the roughness height by a following ejection event. [ABSTRACT FROM AUTHOR]

For the last five decades, a number of overflow stepped chutes were built because the staircase shape is conducive to reduced construction costs and increased rate of energy dissipation. The stepped chute operations are characterised by air‐water flows that are highly turbulent flows with a large rate of energy dissipation, in comparison to smooth chutes. Herein, physical measurements were performed in a large‐size 1 V: 0.80H stepped chute model, with a steep slope typical of modern concrete gravity dams. The results are compared to visual observations of prototype spillway operation under Froude similar conditions. The detailed two‐phase flow measurements were conducted to characterise finely the self‐aeration and air diffusion process downstream of the inception region of free‐surface aeration. The bubble count rate profiles scaled with the instantaneous void fraction variance, and the relationship was biased close to the stepped invert under the influence of large‐scale vortical structures. The rate of energy dissipation was carefully estimated based upon the two‐phase flow measurements and the results are compared to earlier results on similar steep invert slopes and prototype data estimates. At the downstream end of the stepped chute, the rate of energy dissipation ranged from 43 to 46%, i.e. more than twice that on a smooth-invert chute for a similar chute length and discharge range. Characteristics of self-aerated stepped chute flows for dc/h = 1.3—(I) Prototype flow at Hinze Dam (Re = 4.0 × 107); (II) Air-water flow properties in the large-size laboratory model (1:15) stepped spillway (Re = 6.1 × 105) Article Highlights: Air-water measurements were performed in a large‐size 1V:0.8H stepped chute model. The results are compared to visual observations of prototype stepped chute operation under Froude similar conditions. The energy dissipation was estimated, taking into account the air-water flow properties inclusive of air-water pressure and velocity correction coefficients. The rate of energy dissipation ranged from 43 to 46%, i.e. more than double that on a smooth-invert chute. The contribution paves the way for future research to close the knowledge gap on self-aerated chute flows in full-scale structures. [ABSTRACT FROM AUTHOR]

In simulations using the particle finite element method (PFEM) with node‐based strain smoothing technique (NS‐PFEM) to simulate the incompressible flow, spatial and temporal instabilities have been identified as crucial problems. Accordingly, this study presents a stabilized NS‐PFEM‐FIC formulation to simulate an incompressible fluid with free‐surface flow. In the proposed approach, (1) stabilization is achieved by implementing the gradient strain field in place of the constant strain field over the smoothing domains, handling spatial and temporal instabilities in direct nodal integration; (2) the finite increment calculus (FIC) stabilization terms are added using nodal integration, and a three‐step fractional step method is adopted to update pressures and velocities; and (3) a novel slip boundary with the predictor–corrector algorithm is developed to deal with the interaction between the free‐surface flow with rigid walls, avoiding the pressure concentration induced by standard no‐slip condition. The proposed stabilized NS‐PFEM‐FIC is validated via several classical numerical cases (hydrostatic test, water jet impinging, water dam break, and water dam break on a rigid obstacle). Comparisons of all simulations to the experimental results and other numerical solutions reveal good agreement, demonstrating the strong ability of the proposed stabilized NS‐PFEM‐FIC to solve incompressible free‐surface flow with high accuracy and promising application prospects. [ABSTRACT FROM AUTHOR]

Tensile instability is one of the major obstacles to particle methods in fluid simulation, which would cause particles to clump in pairs under tension and prevent fluid simulation to generate small-scale thin features. To address this issue, previous particle methods either use a background pressure or a finite difference scheme to alleviate the particle clustering artifacts, yet still fail to produce small-scale thin features in free-surface flows. In this article, we propose a dual-particle approach for simulating incompressible fluids. Our approach involves incorporating supplementary virtual particles designed to capture and store particle pressures. These pressure samples undergo systematic redistribution at each time step, grounded in the initial positions of the fluid particles. By doing so, we effectively reduce tensile instability in standard SPH by narrowing down the unstable regions for particles experiencing tensile stress. As a result, we can accurately simulate free-surface flows with rich small-scale thin features, such as droplets, streamlines, and sheets, as demonstrated by experimental results. [ABSTRACT FROM AUTHOR]

Numerous indirect methods for estimating the bed shear stress using velocity or turbulent stress profiles have been suggested in previous research. Although these methods have proven effective for simple boundary‐layer‐type flows, their efficacy in complex flow scenarios remains largely unexplored. This study aimed to evaluate the predictive capabilities of three popular indirect bed‐shear‐stress estimation methods—the logarithmic law, Reynolds shear stress (RSS), and turbulence kinetic energy (TKE) techniques—in a complex flow environment involving an obstacle in an open channel, producing massive flow separation and unsteady vortex shedding. To circumvent the difficulties of direct bed shear‐stress measurements, the reference bed shear stress was obtained from a high‐resolution wall‐resolving large‐eddy simulation (LES) data set. The key findings of this study are as follows: First, the logarithmic law and TKE methods were effective only in regions where the streamlines were almost parallel to the primary flow direction. Second, the ratio of the bed shear stress to TKE varied significantly in space in complex‐flow regions, rendering TKE methods virtually ineffective in these areas. Third, the RSS methods successfully reproduced the LES‐computed bed shear stress distributions, both qualitatively and quantitatively. Fourth, the accuracy of the RSS methods was influenced by two critical factors: (a) the incorporation of the transverse RSS component in the RSS extrapolation and (b) the selection of extrapolation techniques. Finally, this study recommends the use of RSS methods employing two‐point extrapolation for bed shear‐stress estimation in complex flows. Key Points: Indirect methods were tested to estimate bed shear stress in a complex flow setting using high‐resolution large‐eddy simulation dataLog‐law and turbulence kinetic energy methods were effective for straight flow regions but unsuitable for regions with complex flowsThe Reynolds shear stress method using two‐point extrapolation with a lower point close to the bed was the most effective [ABSTRACT FROM AUTHOR]

Bu çalışmada bitki örtüsünün, dikdörtgen bir açık kanal üzerindeki akım özelliklerine olan etkisi, Hesaplamalı Akışkanlar Dinamiği analizi kullanılarak incelenmiştir. Hesaplamalı Akışkanlar Dinamiği (HAD) için ANSYS Fluent yazılımı kullanılmıştır. Akımın üç boyutlu, sıkışmayan, türbülanslı ve kararlı olduğu kabul edilmiştir. Sayısal çalışma literatürde yapılan deneysel bir çalışma ile doğrulanmıştır. Sayısal çalışmanın deney sonuçlarını başarılı bir şekilde tahmin ettiği gözlemlenmiştir. Sayısal çalışma ve ölçüm sonuçları arasındaki bağıl hata %10’un altında bulunmuştur. Yapılan sayısal çalışmalar sonucunda, bitki örtüsünün kanalın akım ve türbülans özelliklerini önemli ölçüde değiştirdiği gözlemlenmiştir. Bitki örtüsü olan bölgelerde, su yüzeyinde hızların çok düşük olduğu, yaprak örtüsünün altında kökler arasında ise hızların yüksek olduğu ve maksimum hızın 0,1177 m/s ile bu bölgede gerçekleştiği tespit edilmiştir. Ayrıca türbülans viskozitesinin serbest alanlarda fazla olduğu gözlemlenirken türbülans enerji kırılımının katı-sıvı temas bölgelerinde fazla olduğu görülmüştür. Bu çalışma, açık kanal akışının bitki örtüsüyle etkileşimini anlamak ve açık kanal sistemlerinin hidrolik açıdan performansını geliştirmek için önemli bilgiler sağlamaktadır.

Surface tension and wetting are dominating physical effects in microscale and nanoscale flows. We present an efficient and reliable model of surface tension and equilibrium contact angles in smoothed particle hydrodynamics for free-surface problems. We demonstrate its robustness and accuracy by simulating several three-dimensional free-surface flow problems driven by interfacial tension. [ABSTRACT FROM AUTHOR]

New experiments in highly turbulent, steady, subcritical and uniform water open-channel flows have been carried out to measure the mean turbulent kinetic energy (TKE) budget of sediment-laden boundary layer flows with two sizes (dp =3 mm and 1 mm) of Plexiglas particles (relative density = 1.192). The experiments covered energetic sediment transport conditions (Shields number of 0.35 < θ < 1.2) ranging from non-capacity to full-capacity flows in bedload-to-suspension-dominated transport modes (suspension number of 0.5 < ws/u∗ < 1.3 where ws is the settling velocity and u∗ is the friction velocity) and for weakly to highly inertial, finite size turbulence-particle conditions (Stokes number of 0.110 where η is the Kolmogorov length scale). It was shown that the effects of sediments on the TKE budget are very pronounced in all large particle experiments for which a bedload layer of several grain diameter thickness is developed above the channel bed. When compared with the corresponding reference clear-water flows, the TKE shear-production rate for the 3 mm particle flows is strongly reduced in the wall region corresponding to the bedload layer. This turbulence damping is seen to increase with sediment load until full capacity for flows with constant Shields value, as well as with Shields number value. Inside this damped TKE shear-production zone, a distinct peak of maximal turbulence production appears to coincide with the upper edge of the bedload layer delimited by a sharp gradient in mean sediment concentration. This vertically upshifted peak of TKE production is accompanied by an enhanced net downward oriented TKE flux when compared with the reference clear-water flows. The downward diffused TKE is found to act in the bedload layer as a local energy source in reasonable balance with the sediment transport term. The mechanism behind this downward TKE transport was further analysed on the basis of coherent flow structure dynamics controlled by ejection- and sweep-type events. The agreement between the height of downward directed mean TKE flux and the height below which sweep-type events dominate the Reynolds shear-stress contribution over ejections, revealed the leading role played by sweeps in mean TKE transport. This agreement holds for all reference clear-water flows supporting the well-known wall-roughness-induced dominance of the sweep contribution in turbulent, rough clear-water boundary layer flows. Furthermore, for all 3 mm particle flows, the two referred to transition levels were significantly and similarly upshifted to the upper edge of the bedload layer. Only for these sediment-laden flows, the bedload layer thickness is seen to exceed the wall-roughness sublayer of the reference clear-water flows. This supports a strong analogy between wall-roughness effects in clear-water flows and bedload layer effects in sediment-laden flows, on the mean TKE budget induced by a similarly modified coherent flow structure dynamics. The bedload layer-controlled wall roughness is finally confirmed by the good prediction of the wall-roughness parameter ks of the logarithmic velocity distribution. An empirical formulation fitting the presented measurements is presented, valid over the range of Shields number values covered herein. [ABSTRACT FROM AUTHOR]

Measuring the flow field not just above but also inside the canopy of rough beds in open-channel flows is challenging when optical access from below or the side is not possible. To this end, a new stereo-PIV arrangement was implemented and tested. To optically access the area in between the roughness elements, a top-viewing stereo-PIV system was installed at a steep viewing angle of 70 ∘ . Furthermore, a glass plate was installed at the water surface to avoid random image distortions from surface waves. Finally, in-house-produced low-cost fluorescent particles were used to filter out laser reflections on the canopy's surface. To validate the stereo-PIV measurements with respect to the steep viewing angle of the stereo cameras, the instantaneous flow field above a bed of spheres was measured simultaneously with the stereo-PIV system and with a third side-looking camera for standard 2D-PIV processing. Two different water depths and two different Reynolds numbers were investigated under uniform flow conditions. Finally, to assess the influence of the glass plate on the flow, 2D-PIV measurements were performed with and without the glass plate. It is shown that the steep viewing stereo PIV can properly reconstruct the instantaneous, mean and turbulent statistics except for the vertical normal turbulent stresses, which are overestimated due to peak-locking errors. Also, the boundary layer developing below the glass plate induces a slight acceleration in the bulk flow, which can be considered negligible for higher water depths. In all instances, the flow acceleration does not affect the near-bed region. [ABSTRACT FROM AUTHOR]

The study of kinetic sorptive effects on the transport phenomena of reactive solute has numerous real-world applications, including in the industrial and environmental sectors. These kinds of investigations become more realistic when an oscillatory pressure gradient with both the reversible and irreversible reactions at the channel walls is considered in a magnetohydrodynamics flow. In the past, Ng and Yip [J. Fluid Mech. 446, 321–345 (2001)] studied the effect of sorptive phase exchange at boundaries on the solute transport phenomena in an open-channel flow using Mei's multiple-scale homogenization technique. They considered fluid flows without magnetic field and boundary absorption. This work uses the above-mentioned method to investigate the phase exchange kinetics of Taylor dispersion phenomena in a two-dimensional magnetohydrodynamics fluid flowing through a parallel channel. The paper discusses how various parameters and dimensionless numbers, such as the Hartmann, oscillatory Reynolds, and Damkohler, affect the flow velocity, transport coefficient, multi-dimensional concentration distributions, and transverse variation rate. Due to the strong magnetic field, the flow velocity and Taylor dispersivity are adversely affected and conspicuously reduced. Additionally, for large Damkohler numbers, the total dispersion coefficient and the Taylor dispersion coefficient both decrease. However, the longitudinal concentration distribution rises with the Hartmann number and partition coefficient. It is worth noting that in the presence of unequal boundary absorption, there is no occurrence of transverse symmetry in solute concentration at any given time. Controlling various processes of tracer dispersion in environmental systems, especially water purification and the chemical industry, may benefit from these intriguing findings. [ABSTRACT FROM AUTHOR]

Climate change will be pronounced in sub-arctic and arctic regions. Consequently, a shorter ice-cover period, increased precipitation and changes in the timing and magnitude of discharge are expected. These hydroclimatic changes can have an impact on sediment transport in northern rivers. Studying spatial and temporal variation of the processes in low-flow open-water and ice-covered conditions is crucial to improve the prediction of future changes. The investigation of under-ice conditions has been challenging and new approaches for their measurement are much needed. We analyse the spatial sediment transport in a meandering subarctic river during different flow conditions, i.e., low flow open-channel during autumn and ice-covered during winter. We use one-dimensional (1D) morphodynamic models with imagebased sediment transportation data sets. We also simulate sediment transport with different ice thicknesses to better understand the overall bedload transport in a subarctic river in mid-winter conditions. Simulations for the studied meander bend showed a considerable flow-driven decrease of sediment transport in ice-covered conditions when compared to open-water conditions. Erosion was more pronounced in open-water conditions and deposition was the prevailing process in ice-covered conditions. When an additional increase in ice thickness was simulated, bedload increased, because the thicker ice narrowed the river channel substantially and thus leading to an increase in flow velocity and shear forces. Instead of solely relying on the sediment samples, the additional consideration of an image-based sediment data set enabled a more reliable model calibration in ice-covered conditions. This encourages further usage of image-based methods for sediment transport estimations, especially in ice-covered conditions. In the future, changes in river-ice can be expected to decrease under-ice sediment load but increase annual open-water sediment loads. The increasing summative sediment transport of small arctic and subarctic rivers can have significant consequences on the downstream waterbodies. [ABSTRACT FROM AUTHOR]