Open Channel Flow Research Articles

Characteristics of hydraulic jump in asymmetrical trapezoidal channel with rough beds: experimental investigations

Understanding the dynamics of hydraulic jumps is crucial for optimizing the design of stilling basins in dams, enhancing energy dissipation efficiency, and reducing corrosion risks in hydraulic structures. This work aims to investigate the effect of bed geometry and roughness on the properties of hydraulic jump in an asymmetric trapezoidal channel, including parameters such as sequential depths, roller length and energy loss. Experiments were carried out under open channel flow conditions using three different bottom roughness element heights and mm. The channel's bottom is inclined transversely with a slope of covering a wide range of inflow Froude Number . Results indicate that the increase in bottom roughness leads to a decrease in the subsequent depth ratio by 28.91% compared to a hydraulic jump in a smooth bed. It was also found that the average reduction in roller length on the shallow and deep sides is 21.62% and 20.4%, respectively. Increasing the height of the roughness element enhances the relative energy dissipation by 8.53%. Finally, empirical equations were developed to describe hydraulic jump characteristics based on the Froude number and roughness element height, aiding in the optimal design of stilling basins.

Experimental investigation of turbulent energy spectra affected by submerged vegetation in shallow open channel flows

In the presence of vegetation in open channel flows, various physical processes, such as sediment transport, may be dominated by large-scale eddies, of which mechanisms are not well understood at present. In this study, we aimed to explore vegetation-affected turbulence from the perspective of energy spectral analysis. First, we conducted a series of laboratory experiments of open channel flows with submerged vegetation by varying the flow rate, water depth, and vegetation density. With flow velocities measured using the particle image velocimetry (PIV) technique, energy spectral analyses were then performed over several representative locations in the flow field. The results show that the Kelvin–Helmholtz (KH) vortices dominate the flow in the surface layer, while the shedding wake controls the flow in the vegetation layer, particularly downstream of individual vegetation stems. The normalized frequency of the KH vortices increases for flows with dense vegetation, of which the peak value, when normalized as the Strouhal number, has an average of 0.21. Furthermore, by applying Taylor's frozen turbulent hypothesis, it is shown that both the scale of the KH vortices and the penetration depth reduce when the vegetation becomes dense. Within the vegetation layer, the minimum of the peak streamwise wavelength is observed to be related to the shedding wake, while its maximum scales with the size of the penetrating KH vortices.

Hydrokinetic energy applications within hydropower tailrace channels: Implications, siting, and U.S. potential

Hydropower tailrace channels are unique and attractive locations for hydrokinetic energy harvesting due to fast currents, scheduled flow releases, proximity to existing structural and electrical infrastructures, and low risk of additional environmental impacts. However, energy-extracting devices create flow resistance, inducing a small but measurable water level increase which may diminish the available hydraulic head and reduce hydropower generation, defeating the initial value proposition. This study combines a one-dimensional momentum balance approach with the backwater equation for surface-varying open channel flow to analyze the water level increase and determine the optimal turbine siting distance that maximizes the net power production (balancing hydropower loss vs. hydrokinetic gain), as a function of the channel hydraulic conditions and the hydrokinetic turbine characteristics. Finally, using a subset of sites from the U.S. hydropower fleet, we provide a high-level estimation of the hydrokinetic potential available in tailraces in the United States and discuss two case studies. This work advocates for the adoption of hydrokinetic turbines downstream of dams as an opportunity to increase energy production at existing plants and Non-Powered Dams (NPDs) with minimal structural intervention, and, alternatively, as viable sites for large-scale field testing for hydrokinetic devices.

Turbulent flow structure around a single submerged angled spur dike under ice cover

Abstract This experimental study examines the velocity fields around the single submerged spur dike in a large-scale flume under three flow conditions: open channel, smooth ice-covered, and rough ice-covered. The effects of dike orientation were investigated for alignment angles of 90°, 120°, and 135°. Instantaneous three-dimensional velocity components were recorded using an acoustic Doppler velocimeter. Results show that the spur dikes generate distinct transverse flow regions in the streamwise, lateral, and vertical directions. Alignment angles greater than 90° reduced streamwise velocity near the dikes, while the frontal surface of the dike tip exhibited increased velocity magnitudes. Downstream, significant variations in Reynolds shear stress were observed, driven by flow separation and the formation of a recirculation wake zone. Quadrant analysis revealed that under ice-covered conditions, turbulent interactions near the dike tip were dominated by ejection and sweep events, whereas sweep events were more prevalent in open channel flows, influencing overall flow dynamics.

An open source electrochemical channel flow cell setup for kinetics studies. Application to investigations on oxygen electrocatalysis

Herein, an electrochemical channel flow cell setup that allows for conducting electrochemical investigations up to 80°C and pressurized gases up to 3 bar is presented in details, including technical drawings and list of parts, in an attempt to facilitate the adoption of such setup by the community for electrochemical/electrocatalytic kinetic studies. The oxygen reduction reaction (ORR) on a commercial Pt/C catalyst, chosen as a model reaction, was investigated to demonstrate the reliability of the experimental setup, including the hydrodynamic properties, to provide hands on practical guidelines to carry out experiments, and, on the other hand, to illustrate the capabilities of this electrochemical setup for an assessment of basic quantities. Among the various quantities that have be determined experimentally for the ORR, a monotonic decay of the activation enthalpy and bell-shaped variation of the entropy of activation were resolved as the overpotential for the ORR increases. These fundamental thermodynamic/kinetic data are briefly discussed within the frame of the established reaction mechanism and can serve as a feed for the benchmarking of the outputs from theoretical/computational models. Furthermore, a remarkable agreement was obtained between the change in the activation free Gibbs energy determined for the ORR with the flow cell setup and the kinetic region of fuel cell polarization curve obtained with the same Pt/C catalyst embedded in the cathode of an a hydrogen proton exchange membrane fuel cell. This enables potentially a bridge of the environmental gap existing between model experiments conducted at active material level in contact with liquid electrolyte and experiments with porous gas diffusion electrode embedding the same active material that are employed in practical device.

Influence of particle density on turbulence characteristics over a rough surface

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.

Turbulent stratified open channel flow with solar heating up to Pr=7 using Direct Numerical Simulation

This paper investigates the turbulent structure of stratified open-channel flow subjected to a radiative volumetric heat source modelled by the Beer–Lambert law, for Prandtl numbers (Pr) varying from 0.07 to Pr=7. Direct Numerical Simulation (DNS) was employed to model the open-channel flow. To overcome the increased computational resources required to resolve the thermal fields when Pr>1, a multi-resolution method using quadratic interpolation was employed to resolve the temperature and momentum fields on different spatial and temporal resolutions. This scheme was implemented in an in-house computational fluid dynamics (CFD) code. To further reduce the computation cost, the DNS of Pr=2.2 and 7 fluids were initialised using the outputs of minimal channel simulations. The simulations were conducted for Pr=0.07, 0.22, 0.71, 2.2, and 7 under neutral (λ=0), near-neutral (λ=0.1), and stable (λ=0.5) thermal stratification. The results demonstrate that Pr significantly affects the flow structure and turbulence characteristics of stratified flows, particularly near the free surface. This includes higher velocity, temperature gradient, and buoyancy effects for Pr=7 compared to lower Pr values. For stratified Pr=7 flow, examination of the Reynolds stresses and turbulent heat flux reveals significant damping of turbulence near the surface, with flow displaying near-laminar behaviour.

Modeling of non-equilibrium suspended sediment transport process in open channel flows with vegetation

A mathematical model based on advection-diffusion theory is established to study the non-equilibrium sediment transport process in vegetated channels. The effects of vegetation on velocity distribution and sediment diffusion coefficients were considered, respectively. Validation against experimental data from flume studies confirms the model's ability to accurately predict the longitudinal sediment deposition rate and the vertical distribution of suspended sediment concentration (SSC). A comparative analysis of three sediment diffusion coefficient formulations indicates that the linear-exponential formula provides a more precise estimate of εsz, and the linear-exponential formula performs well in predicting the turbulent diffusion coefficients of both rigid and flexible vegetation when gently swaying. Moreover, the distance required for SSC to regain equilibrium is influenced by the submergence level of the vegetation canopy. At lower submergence levels, the canopy shear vortices significantly affect the vertical exchange of sediment, and the sediment diffusion coefficients exhibit pronounced stratification near the vegetation canopy. An increase in vegetation density at these lower submergence levels intensifies the shear vortices, thereby extending the distance needed for SSC to reach equilibrium. At higher submergence levels, the impact of canopy shear vortices is lessened, which reduces sediment diffusion coefficient stratification characteristics, and the flow is similar to rough boundary layer flow. An increase in vegetation density increases flow resistance, which shortens the distance required for SSC to attain equilibrium. However, further efforts are required to explore turbulent characteristics with highly flexible vegetation motion and the grain size distribution of non-uniform sediments in vegetated flows.

Wake dynamics of side-by-side hydrokinetic turbines in open channel flows

Lateral placement of hydrokinetic turbines is an interesting topic, as the blockage effect can increase the flow speed and increase the power coefficient (CP) for neighboring turbines. This study investigates wake dynamics in hydrokinetic turbine arrays with single- (1T), double- (2T), and triple-turbine (3T) configurations under various tip speed ratios (λ = 3.5, 5.8, and 7.1) using large eddy simulation coupled with the actuator line (AL) model. Results indicate that CP increases as lateral spacing decreases, which highlights the advantages of tighter lateral placement. The CP of the 3T-S turbine (the side turbine in the 3T configuration) is larger than those of the other configurations, following the trend CP,3T−S>CP,3T−M>CP,2T>CP,1T, which reflects a growing blockage effect with more turbines. Wake dynamics are analyzed using time-averaged and instantaneous methods. In 3T scenarios, blockage enhances turbulence kinetic energy, facilitating faster wake recovery, aided by turbine interference. Mean kinetic energy budget analysis shows that 3T-S wakes recover fastest due to increased turbulent convection. For instantaneous analysis, pre-multiplied power spectral density reveals vertical meandering begins at approximately 3D (D is the rotor diameter) and horizontal meandering starts near 4D, with a dominant frequency of St=0.28. Integral length scales show an initial increase followed by a downstream decrease, with minima marking the onset of wake meandering. Dynamic mode decomposition analysis reveals that high-frequency disturbance amplitudes increase with the number of turbines. At the optimal λ, wake effects dominate over inflow effects.

Experimental Tests of Lateral Bedload Transport Induced by a Yawed Submerged Vane Array in Open-Channel Flows

Experimental Tests of Lateral Bedload Transport Induced by a Yawed Submerged Vane Array in Open-Channel Flows

Numerical investigation of turbulent flow over a randomly packed sediment bed using a variable porosity continuum model

A large eddy simulation (LES) is performed for a turbulent open channel flow over a porous sediment bed at permeability Reynolds number of ReK∼2.56 (Reτ = 270) representative of aquatic systems. A continuum approach based on the upscaled, volume-averaged Navier−Stokes (VaNS) equations is used by defining smoothly varying porosity across the sediment water interface (SWI) and modeling the drag force in the porous bed using a modified Ergun equation with Forchheimer corrections for inertial terms. The results from the continuum approach are compared with a pore-resolved direct numerical simulation (PR-DNS) in which turbulent flow over a randomly packed sediment bed of monodispersed particles is investigated [Karra et al.,J. Fluid Mech. 971, A23 (2023)] A spatially varying porosity profile generated from the pore-resolved DNS is used in the continuum approach. Mean flow, Reynolds stress statistics, and net momentum exchange between the freestream and the porous bed are compared between the two studies, showing reasonably good agreement. Small deviations within the transitional region between the sediment bed and the freestream as compared to the PR-DNS results are attributed to the local protrusions of particles in a randomly packed bed that are absent in the continuum approach but are present in the PR-DNS. A better representation of the effective permeability in the top transition layer that accounts for roughness effect of exposed particles is necessary. The continuum approach significantly reduces the computational cost, thereby making it suitable to study hyporheic exchange of mass and momentum in large scale aquatic domains with combined influence of bedform and bed roughness.

Vertical concentration distribution of fine settling particles in a pulsatile laminar open channel flow

Sedimentation in river and drainage systems frequently increases flood risks, making the study of particle dispersion crucial for effective flood damage control. In the present research, the transport of fine settling particles in a laminar, periodic flow through an open channel is analytically investigated using the multi-scale homogenization method. To investigate how settling velocity affects the dispersion process of fine particles in a tidal wetland, Dhar et al. (2022) studied the dispersion coefficient and mean concentration of the settling particles applying the method of moments. The mean and transverse real concentration distributions of settling particles are analytically derived from the governing equation, and the influence of settling velocity, oscillation Reynolds number, and Schmidt number on the dispersivity and concentration profile of the settling particles is investigated. The results show a vertical non-uniformity of longitudinal concentration distribution due to the introduction of settling velocity. It is also observed that the sedimentation effect for purely oscillatory flow is negligibly small compared to that of the steady and oscillatory flow with a nonzero mean. Pulsatile behavior is observed in the difference rate profile between Taylor’s mean and present mean concentration. The study sheds light on the behavior of settling particles and can be useful for understanding sedimentation and wastewater treatment processes.

Analysing Turbulence Patterns in Nature‐Like Fishways: An Experimental Approach

ABSTRACTNature‐like fishways are an important measure for restoring fish passage, mitigating the impacts of barriers, and providing valuable habitat benefits in a more natural and effective way than traditional technical fishways. Their ecological advantages make them a preferred solution in many river restoration projects. The turbulence at the fishway's pool is a key challenge in the design of fishways. This study evaluated the hydraulic performance of the nature‐like fishway section of the Zongyang Fishway Project in China. This utilized a trapezoidal cross‐section with a 1:242 bottom slope, 1:2 side slopes, and an operating water depth of 1–3 m. The bottom and sides were paved with 0.2–0.5 m diameter pebbles to create suitable habitat for bottom‐dwelling fish. The target design velocity was 0.7–0.9 m s−1. A physical model was constructed to assess the hydraulic characteristics of the nature‐like fishway, including flow velocities within the slots and turbulence levels in the pools. The results showed that the slot velocities were within the target range, the head loss was parallel to the bottom elevation, and the flow field near the bottom mimicked technical fishway conditions, whereas the surface flow resembled open channel flow. Turbulence intensity remained below 60% of the design velocity. These findings provide valuable insights into the hydraulic performance and suitability of this nature‐like fishway design for facilitating fish passage of the target freshwater species along with directly aiding to SDGs 6 and 14.

Physics-informed data-driven reconstruction of turbulent wall-bounded flows from planar measurements

Obtaining accurate and dense three-dimensional estimates of turbulent wall-bounded flows is notoriously challenging, and this limitation negatively impacts geophysical and engineering applications, such as weather forecasting, climate predictions, air quality monitoring, and flow control. This study introduces a physics-informed variational autoencoder model that reconstructs realizable three-dimensional turbulent velocity fields from two-dimensional planar measurements thereof. Physics knowledge is introduced as soft and hard constraints in the loss term and network architecture, respectively, to enhance model robustness and leverage inductive biases alongside observational ones. The performance of the proposed framework is examined in a turbulent open-channel flow application at friction Reynolds number Reτ=250. The model excels in precisely reconstructing the dynamic flow patterns at any given time and location, including turbulent coherent structures, while also providing accurate time- and spatially-averaged flow statistics. The model outperforms state-of-the-art classical approaches for flow reconstruction such as the linear stochastic estimation method. Physical constraints provide a modest but discernible improvement in the prediction of small-scale flow structures and maintain better consistency with the fundamental equations governing the system when compared to a purely data-driven approach.

Parametric Optimization For Power Generation Of Flow Induced Vibration Energy Harvester

Flow-induced vibration occurs when the motion of fluids through a structure induces oscillations or vibrations in the structure. An effective flow-induced vibration energy harvester has substantial challenges due to the river's irregular velocity flows. It is not practicable to use one parameter for all velocities. This work presents the testing of a flow-induced vibrational energy harvester in laminar flow using two circular cylinders positioned in tandem within an open-channel flow. A CFD simulation using COMSOL Multiphysics was performed for the proposed parameter. A comprehensive simulation run at multiple Reynolds numbers with varying gap lengths between the bluff bodies is studied to determine the maximum power generated. Simulation results show that the optimal gap lengths for Re 60, 80, 100, 120, 140, and 160 are 8.5, 6.0, 3.0, 3.0, 3.5, and 4.5, respectively. These gap lengths result in power outputs of 0.0315 W, 2.616 W, 1.899 W, 0.6552 W, 0.5018 W, and 0.3782 W. By demonstrating the relationship between Reynolds number and gap length, this study provides important information for maximising the energy harvesting from flow-induced vibration (FIV).

Modeling transient mixed flows in sewer systems with data fusion via physics-informed machine learning

Transitions between free-surface and pressurized flows, known as transient mixed flows, have posed significant challenges in urban drainage systems (UDS), e.g., pipe bursts, road collapses, and geysers. However, traditional mechanistic modeling for mixed flows is challenged by the difficult integration of multi-source data, complex equation forms for the discovery of dynamic processes, and high computational demands. In response, we proposed a data-driven model, TMF-PINN, which utilizes a Physics-Informed Neural Network (PINN) to simulate and invert Transient Mixed Flow (TMF) in sewer networks. This model integrates experimental data, simulation results and Partial Differential Equations (PDEs) into its loss function, leveraging the extensive data available in smart urban water systems. A status factor (α) has been introduced to seamlessly link open channel and pressurized flow dynamics, facilitating rapid adjustments in wave speed. On this basis, Fourier feature extraction and quadratic neural networks have been employed to capture complex dynamic processes featuring high-frequency. Validation through three classical cases using the Storm Water Management Model (SWMM) and comparisons with finite volume Harten-Lax-van Leer (HLL) solver reveal that the proposed model circumvents the constraints of spatiotemporal resolution, yielding accurate flow field predictions.

Numerical simulation of open channel basaltic lava flow through topographical bends

In this study, we utilised computational fluid dynamics to investigate the behaviour of open-channel basaltic lava flows navigating bends on shield volcanoes. Our focus was on understanding the relationship between flow velocity, rheology, and bend geometry. Employing a simple Force Balance Model (FBM), which considers the equilibrium between hydrostatic pressure and centrifugal force, we accurately approximated the changes in the height of the lava’s free surface through various bend geometries. Our analysis includes examining the influence of channel depth, width, and bend radius on the flow, revealing that variations in these parameters significantly affect the flow’s vertical displacement. Additionally, the bend sector angle emerged as a critical factor, indicating a minimum angle necessary for the flow to fully develop before exiting the bend.Further, we assessed the applicability of the Shallow Water Equations (SWE) for modelling the inertial displacement of the lava flow in bends, finding a good fit. The study extended to comparing the FBM’s predictions of the tilt angle of the flow’s free surface with the SWE results, showing notable agreement under specific conditions, particularly at a bend angle of 90 degrees. The impact of fluid density was also considered, revealing that density is a contributing factor to the development of the wetted line in the bend, a factor that is not captured by the simple FBM model. Finally, we explored different rheologies akin to natural lava flows, such as viscoplastic flow, and determined that factors like yield stress, consistency index, and power law index have a small impact on the flow behaviour in a steady-state condition within a bend.

Numerical simulation of an effective transform mechanism with convergence analysis of the fractional diffusion-wave equations

In the current study, we solve two very important mathematical models, such as the time fractional-order space-fractional telegraph and diffusion-wave equations using a reliable technique called the Adomian decomposition natural method (ADNM), which combines Adomian decomposition and natural transform. The diffusion wave equation describes the flood wave propagation, which is used in solving overland and open channel flow problems. For this reason, it is critical to fully understand and effectively solve the diffusion wave equations. Because telegraph equations are crucial for modeling and developing voltage or frequency transmission, they are widely used in physics and engineering. Furthermore, the designing process is greatly impacted by the uncertainty in the system parameters. For nonlinear ordinary differential equations based on the theorem of Banach fixed point, we provide existence and uniqueness theorem proofs. The present approach has been successfully used to explore exact solutions for time fractional-order and space fractional-order applications. The results show how effective and valuable the ADNM. This paper presents a methodology that will be used in future work to address similar nonlinear problems related to fractional calculus.

Modified stochastic diffusion particle-tracking model (MSDPTM) incorporating energy cascade theory and eddy intermittency for suspended sediment transport in open channel flow.

This study presents a modified stochastic diffusion particle tracking model (MSDPTM) that incorporates energy cascade theory to more accurately simulate suspended sediment transport. The impact of turbulent eddies on sediment particles is an intermittent process, which is also considered in this study. The study examines the time correlation between eddies using eddy turnover time and finds that closer-scale eddies exhibit higher correlations than those farther apart. The statistical properties of particle movement, such as the ensemble mean and variance of particle trajectories, have been calculated and compared with the stochastic diffusion particle tracking model (SDPTM) results. Notably, MSDPTM with intermittency demonstrates a significantly larger ensemble mean of particle trajectories in the streamwise direction than other particle tracking models. The proposed model is validated through comparison with available data, showing its enhanced performance. The results of the simulation indicate that MSDPTM outperforms SDPTM, especially when the intermittency effect of eddies is considered.

Morphological properties of two-dimensional and three-dimensional bedforms in open channel flow: A flume experiments study

Bedforms are formed by sediment particles under the action of flow, which in turn affect flow and sediment movement. However, the fundamental mechanisms behind the formation and development of bedforms under varying flow conditions, the interconnection between sediment particle movement and bed morphology development, as well as the influence of bedforms on flow and sediment transport, are still not well understood. In the current study, the moveable bed load transport flume experiments under different flow conditions were done, and the development processes of two-dimensional and three-dimensional dunes formed under different flow intensities were simulated. The detailed structure of the bedforms was measured by laser scanning technology, the characteristics of the bedforms were analyzed in detail, and the relations between the formation of the bedforms and the movement of sediment particles are discussed. The results found that the correlation coefficients of the longitudinal profile curve can serve as a quick reference for distinguishing two-dimensional and three-dimensional dunes. When the crestline ratio is used as the criterion for two-dimensional and three-dimensional dunes, the relative amplitude of the dune crestline and the included angle with the flow direction should also be comprehensively considered. The lee side angles of dunes calculated using the triangle generalization method and local section tangent method are compared and show that the values obtained by the former method are only about half of that of the latter. It is also found that the lee side angles of dunes are related to the dune height. The superimposed dunes generally exist in the downstream area of the stoss side of the dunes. The local bed slopes on the stoss side of the dunes show reverse slopes. The superimposed dunes improve the local bed height and further increase the reverse slope degree of the stoss side. A streamwise ridge is an important form located in the upstream area of the dunes stoss side, and they are symmetrically distributed on both sides. Multiple streamwise ridges divide the stoss side of the dunes into relatively independent movement areas, restricting the movement of sediment particles to specific regions. According to the distribution characteristics of bed morphologies, the effects of dunes on sediment particle movement and flow energy consumption are analyzed.