Channel Bend Research Articles

Snap-through dynamics of a buckled flexible filament in a channel flow

The flow-induced snap-through dynamics of a buckled flexible filament in a channel flow was explored using the penalty immersed boundary method. Two edge condition distributions were considered for comparison. One edge condition was a simply supported leading edge and a clamped trailing edge (SC); the other condition was two clamped edges. The effects of channel height and bending rigidity on the energy harvesting performance were systematically examined. The presence of the channel wall compresses the activation space of the vortex, leading to the formation of a high shear flow near the wall, which, in turn, strongly influences the wake pattern. In the snap-through oscillation mode, a wake pattern of 2S + 2P is observed in both narrow and broad channels, whereas the mechanism of vortex shedding varies between the two cases. Both cases demonstrate greater critical rigidity and greater elastic energy compared with conditions under external flow, suggesting an enhancement of the energy harvesting performance. The greater energy harvesting ability of the SC case is derived from both the larger deflection and the higher strain energy in this system. The wall effect is inversely proportional to the channel height, becoming nearly negligible when the nondimensional channel height exceeds 2. These findings provide valuable insights into the dynamics of flexible filaments in the channel flow and their potential for energy harvesting applications.

Evaluation of the performance of the Savonius hydrokinetic turbines in the straight and curved channels using advanced machine learning methods

Evaluation of the performance of hydrokinetic turbines is an essential subject in the renewable energy field. In this regard, advanced machine learning methods including hybrid CatBoost and standalone Catboost and linear regression were used for the first time for the straight channel data and channel bend data. The hybrid models were developed using whale optimization (WO), grey wolf optimization (GWO), and Bayesian optimization (BO) algorithms. Sensitivity analysis was also conducted to find the most influential parameters in the best model. Results showed that the hybrid models can predict the goal parameters, including the coefficient of the power (CP), the maximum value of the coefficient of the power (CPmax), and the tip speed ratio corresponding to the Cpmax (TSRmax) better than the standalone models. Among the models, GWO-CB is the best model, even in the k-fold cross-validation scenario. The R2 value of the GWO-CB reached 0.97, 0.94, and 0.84 for the CP, CPmax, and TSRmax, respectively. Among the effective parameters, the lateral position of the returning blade deflector and the number of stages had the maximum and minimum effects on the best model, respectively. The effect of the position of the turbines in the channel bend, which was considered in this research for the first time, was significant in the models.

Backscattering reduction in a sharply bent water wave channel

Backscattering reduction in a sharply bent water wave channel

Two‐Dimensional Numerical Modeling of Large Wood Transport in Bended Channels Considering Secondary Current Effects

AbstractThe modeling of large wood (LW) transport in rivers has received increasing interest from researchers in the last decade due to the widely recognized role of LW concerning flooding risk. For this purpose, few 2D depth‐averaged hydraulic models have been coupled with LW transport models. However, such models usually neglect the effects of secondary currents on LW trajectories in river bends. In this work, the model Iber‐Wood was enhanced to simulate the effects of secondary currents in river bends on LW trajectories. The proposed methodology presents a new formulation for considering secondary current effects on the flow field derived from the Manning formula and considers a new approach for reproducing the surface flow field that develops at channel bends. The enhanced model was tested to reproduce a series of laboratory experiments on wood transport in a sharp channel bend. The methodology introduces two new parameters in the model related to the secondary current effects, that is, the secondary current intensity and the adaptation length. These parameters were calibrated using available data from laboratory experiments. The good agreement between observed and simulated dowel trajectories in a sharp channel bend validated the proposed approach to simulate LW transport in the case of secondary currents.

Effects of Pressure Gradient on Fluid Flow and Energy Distribution in a Bending Square Channel

A precise knowledge on fluid flow and energy distribution in a bending channel is important for the thermal management of various engineering problems. The literature currently lacks a comprehensive understanding on how fluid characteristics and heat transfer in a bending channel are affected by pressure gradients, as well as when and how fluids transit into a turbulent state under continuous pressure gradient. The present study aims to explore the bifurcation structure of the steady solutions, linear stability and velocity distribution of the solutions and the transitional behavior from stead-state to other flow states (i.e., periodic or chaotic) for an extensive domain of the Dean number 0 < Dn ≤ 5000. The geometry of the problem is that the outer and bottom walls are heated while the inner and top are at room temperature. A proper grid analysis and validation are performed as well. The study successfully analyzed four branches of steady solutions where stability exists only in the first branch up to Dn = 2593.3709 and 2- to 7-vortex solutions are observed in the secondary flow. The flow transitions in the unsteady solutions are analyzed exquisitely by performing time-advancement of the solutions followed by inquisition of the phase space of time-dependent solutions. Results show that, if Dn > 2593.3709, the steady-state flow becomes periodic followed by a chaotic solution and 2- to 5-vortex solutions are observed for the unsteady flow. It is noticed that, if Dn > 0, the value of the Nusselt number (Nu) was initially higher on the cooling wall compared to the heated wall and at Dn = 102.67, Nu is found to be equal on both sidewalls and then it started increasing rapidly on the heated walls. The present study figured out how centrifugal force impacts fluid flow for larger pressure gradient, which assists fluid mixing and consequently enhances heat transfer in the fluid.

Study of the convergence of the Meshless Lattice Boltzmann Method in Taylor–Green, annular channel and a porous medium flows

The Meshless Lattice Boltzmann Method (MLBM) is a numerical tool that relieves the standard Lattice Boltzmann Method (LBM) from regular lattices and, at the same time, decouples space and velocity discretizations. In this study, we investigate the numerical convergence of MLBM in three benchmark tests: the Taylor–Green vortex, annular (bent) channel and a porous medium flow. We compare our MLBM results to LBM and to the analytical solution of the Navier–Stokes equation. We investigate the method’s convergence in terms of the discretization parameter, the interpolation order, and the LBM streaming distance refinement. We observe that MLBM outperforms LBM in terms of the error value for the same number of nodes discretizing the domain. We find that LBM errors at a given streaming distance δx and timestep length δt are the asymptotic lower bounds of MLBM errors with the same streaming distance and timestep length. Finally, we suggest an expression for the MLBM error that consists of the LBM error and other terms related to the semi-Lagrangian nature of the discussed method itself.

Confluence simulations based on dynamic channel parameters in the grasslands lacking historical measurements

Technology has greatly promoted ecohydrological model development, but runoff generation and confluence simulations have fallen behind in ecohydrological model development due to limited innovations. To fully understand ecohydrological processes and accurately describe the coupling between ecological and hydrological processes, a distributed ecohydrological model was constructed by integrating multisource information into distributed dynamic process model (DDPM). We mainly describe runoff generation and convergence modules. Based on the improved HBV model and degree-3 h factor method, runoff generation and snow routines were constructed for semiarid grassland basins. In view of meandering and variable steppe river channels and steep hydrological relief characteristics, a confluence module was constructed; the 1-km bend radius equivalent concept was innovatively proposed to unify river channel bend degrees. The daily runoff simulation validation results obtained using two datasets were R2 = 0.947 and 0.932, NSE = 0.945 and 0.905, KGE = 0.971 and 0.680. In the 3-hour flood simulations, the DDPM could better restore small long-distance water flows than the confluence method that did not consider actual river lengths or bend energy losses; the DDPM more accurately simulated the flood peak arrival time than the confluence method that did not consider overflow. The simulated mainstream overflow frequency increased by 0.84/10 years, and significant interaction periods of 10 to 13 years occurred with local precipitation, ecological status, and global climate change. An approximately 2-year lag occurred in the global climate change response. This study helps us further understand and reveal the ecohydrological processes of steppe rivers in semiarid regions.

Numerical study of solution structure and nonlinear behavior of Dean flow with vortex structure in a bending square duct

Fluid flow and heat transfer in bending channels are topics of much research interest because of increasing demand in various fields, particularly in the medical and industrial arenas. This paper presents a numerical study of fluid flow and heat transfer in a bending channel with a square cross section. Numerical calculations using spectral methods were performed for a curvature of 0.001 and a Dean number (Dn) in the range of 0<Dn≤5000. A temperature difference was maintained between the horizontal walls for a Grashof number of Gr = 1000, with the bottom wall heated and the outer and inner walls thermally insulated. Applying Newton–Raphson iteration and path continuation, two branching structures of steady solutions with two to eight vortices were obtained. The first branch comprises multi-vortex up to eight and it occurs at Dn≥3500 while the second branch comprises to multi-vortex up to a maximum of four. The first branch forms symmetric solution while the second branch for its complexity forms asymmetric solutions. For unsteady solutions, time-evolution calculations were performed to investigate the nonlinear behavior, and it was found that with increasing Dn, the unsteady flow experienced various flow instabilities. The time evolution was plotted in phase space to clarify the unsteady flow characteristics. Distinctive contours of the secondary flow patterns, streamwise velocity distributions, and isotherms were also obtained, and the unsteady flow was found to comprise two to six vortices. Finally, convective heat transfer was explored by obtaining temperature contours, and the secondary flow was found to magnify the convective heat transfer significantly. Because of the increase of several secondary vortices in the chaotic solutions, heat transfer occurred markedly in the flow.

A computational modeling on two-dimensional laminar flow and thermal characteristics through a strongly bent square channel

In order to have a precise knowledge on how pressure gradients and buoyancy force affect fluid flow and energy distribution in a bending channel, it is important to perform a comprehensive study on flow characteristics and heat transfer mechanisms that trigger out the transition of fluids into a turbulent state, subject to a sustained pressure gradient. The present paper explores a computational modeling on two-dimensional fluid flow and thermal characteristics in a bent square channel of strong curvature. The Newton–Raphson (N-R) iteration method is applied to obtain a bifurcation structure depending on the pressure-driven force, the Dean number (De), covering 0 < De ≤ 5000. As a consequence, four branches of asymmetric steady solutions are identified for each of the cases of the Grashof number, Gn (=1000, 1500, and 2000), where only the first branch is found to exhibit asymmetric two-vortex solutions while the remaining branches encompass two- to four-vortex solutions. The similarity and disparity in the branching structure are also demonstrated. Then, adopting the Adam–Bashforth (A-B) method together with Crank–Nicholson (C-N) formula, the unsteady solutions (US) have been explored, validated by power spectrum density (PSD) and phase space Within the realm of US, two- and three-vortex solutions are found and these solutions exhibit transitions from steady to chaotic behavior profoundly. Effects of the Grashof number with convective heat transfer (CHT) are also compared. By analyzing the Nusselt number (Nu), it is observed that in case of highly chaotic flow, CHT experiences substantial enhancement. This intensified CHT arises from increased turbulence and mixing, facilitating more efficient thermal energy exchange under such chaotic flow conditions.

Numerical solution of Lock-exchange flow in a curved channel with an obstacle

Gravity currents modify their flow characteristics in the presence of an obstacle. Also, the flow path to the dam reservoirs is not always direct. Since no studies have addressed the feedback between the hydrodynamics of a gravity current in a curved channel and the location effects of the obstacle, in this research, a Lock-exchange density current flows in a 120[Formula: see text] bending channel. The numerical simulation has been performed using OpenFOAM software. The models include no-obstacle curved channel and a curved channel with an obstacle in different positions concerning the increased radius of the curved channel. Results indicated that the obstacle directed the concentration towards the banks, with its maximum value tending from the outer to the inner bank, especially in the tail. The tail longitudinal velocity maximized near the channel bed in areas far from the obstacle, and in the outer bank in areas near it. The secondary flow reduces its lowest and most different pattern observed around the obstacle. In displacing the latter, if the front has at a certain distance, the secondary flow does not change much, but if it has at the channel end, the post-obstacle secondary flow would increase as the obstacle neared the Lock.

Optimizing Rapid Prototype Development Through Femtosecond Laser Ablation and Finite Element Method Simulation for Enhanced Separation in Microfluidics

In recent years, microfluidic systems have emerged as promising tools for blood separation and analysis. However, conventional methods for prototyping microfluidic systems can be slow and expensive. In this study, we present a novel approach to rapid prototyping that combines femtosecond laser ablation and finite element method (FEM) simulation. The optimization of the prototyping process was achieved through systematic characterization of the laser ablation process and the application of FEM simulation to predict the flow behavior of the microfluidic devices. Using a dean-coupled inertial flow device (DCIFD) that comprises one channel bend and three outlets side-channels. DCIF is a phenomenon that occurs in curved microfluidic channels and is considered by the existence of inconsequential flow patterns perpendicular to the main flow direction. The DCIF can enhance the separation efficiency in microfluidic devices by inducing lateral migration of particles or cells towards specific locations along the channel. This lateral migration can be controlled by adjusting the curvature and dimensions of the channel, as well as the flow rate and properties of the fluid. Overall, DCIF can provide a valuable means of achieving efficient and high-throughput separation of particles or cells in microfluidic devices. Therefore, various microfluidics designs that contain different outlet channels were studied in this research to improve blood plasma separation efficiency. Results from imitated blood flow experiments showed positive results for fluid flow and particle separation. The study also found that incorporating three various channel widths is the key to achieving efficient plasma separation, indicating that this result could serve as a guideline for future microfluidics geometry specifications in the field of blood plasma separation. According to the FEM simulation, the highest separation percentage for both microparticle sizes was obtained by incorporating a variable outlet channel width into the same microfluidic device. The FEM simulation revealed that around 95% of the larger microparticles separated while 98% of the smaller microparticles separated. This is consistent with the imitated blood separation results, which showed that 91% of the larger microparticles separated and around 93% of the smaller microparticles were separated. Overall, our results demonstrate that the combination of femtosecond laser ablation and FEM simulation significantly improved the prototyping speed and efficiency while maintaining high blood separation performance.

Geomorphologic evidences and hydrologic reconstruction of Holocene catastrophic flood events in the Yarlung Tsangpo Grand Canyon, Eastern Himalaya

Catastrophic floods from breaching of natural dams on the Namche Barwa and Giala Peri play an important role in shaping high-mountain landforms in the eastern Himalayan syntaxis. However, there is limited knowledge of geomorphologic evidences and magnitude of outburst flooding in the Yarlung Tsangpo Grand Canyon. In this paper, geomorphic impacts of high-magnitude outburst floods (104–106 m3/s) were analyzed using palaeoflood hydrology technology. Well-preserved 2018 Sedongpu (SDP) flood and 2000 Yigong (YG) flood sand bars are charactered by grey sands with parallel laminations, whereas megaflood geomorphic evidences in the Grand Canyon are dominated by massive slackwater deposits and lateral gravel bars. The palaeoflood events were dated to 4.3–2.4 ka, corresponding to the known Holocene megafloods in the lower Yarlung Tsangpo River. These flood ages are obviously younger than most of remnant lacustrine deposits during the late Pleistocene, but consistent with the ages in the top part of palaeolake and glacial moraines of the Namche Barwa. The chronological data help to confirm the highest probability phases of outburst floods from moraine-dammed lakes. The repeated megaflood peak discharges range from 0.5 to 1.1 × 106 m3/s, which are approximately 5–10 times greater than the maximum peak discharge of 2000 YG flood (9.5 × 104 m3/s) and 20–40 times than that of 2018 SDP flood (2.5 × 104 m3/s) in the Medog reach. Megaflood waters are always deepest (∼200 m) and fastest (∼50 m/s), which are at least twice times larger than 2000 YG flood. Higher shear stress (>3.3 kPa) and stream power per unit area (>168 kw/m2) occurred in narrower channel and sharp bend with higher velocity. Our model also predicts some potential erosion and deposition landscapes resulted from floodwaters routing through the Grand Canyon. These results address the geomorphic impacts of catastrophic flood events with magnitudes (104–106 m3/s) in the Yarlung Tsangpo Grand Canyon. Our new palaeoflood geomorphologic evidences provide a key constraint on the age and magnitude of Holocene megafloods in the largest Himalayan River.

A numerical study of battery thermal management system with square spiral ring-shaped liquid cooling plate

The battery thermal management system is critical to the operating safety of power batteries. To alleviate the temperature gradient effect caused by the high local temperature of the battery, a centrally dispersed square-spiral-ring (SSR) mini-channel liquid cooling plate is designed for power batteries in this study. Through the simplification of the battery model, this liquid cooling plate battery thermal management system is investigated numerically. The effects of the number of SSR channel laps, channel width, channel bend radius and inlet mass flow rate on the temperature characteristics of the battery and coolant pressure drop are investigated. The results indicate that increasing the SSR channel laps and narrowing the channel width have a beneficial role in improving the battery and liquid cooling plate temperature distribution. The maximum battery temperature can be significantly dropped and the uniformity of battery temperature distribution can be considerably improved by enhancing the inlet mass flow rate. Moreover, additional branch channels could further improve the uniformity of the temperature distribution and the gradient effect of the battery. The maximum temperature decreases to 33.63 °C and the maximum temperature difference reduces to 6.45 °C during the 2C discharge process at a temperature of 25 °C. Furthermore, the SSR liquid cooling plate with a 5 mm-wide branch channel enables lower maximum battery temperatures and better temperature uniformity with lower pump power consumption than the existing serpentine plate. All these results and evidence provide an option for the development of novel mini-channel liquid cooling plates for battery thermal management.

Effects of relative curvature radius on erosion and sedimentation patterns in a 90o bend with and without bendway weirs

Bendway weirs are low-level transverse structures constructed on the outer bank of a channel bend to improve navigation, create aquatic habitat and control bend migration. This experimental study was aimed at investigating the erosion and sedimentation patterns in a 90° bend by varying the relative curvature radius (i.e. normalized to the channel width), in the absence and in the presence of bendway weirs, under different flow conditions. A series of flat weirs with relative heights of 30% and 70% were considered. The results indicate that as the relative curvature increases, the erosion near the weirs decreases while the point-bar at the inner bend wall extends. Regardless of the weir height, the increase in the relative curvature leads to a deeper scour depth at the tip of the weirs. Bendway weirs with submergence ratio of 70% are found to be the most efficient in protecting the outer bank from erosion.

Insight into the particle-laden turbulent flow statistics in sharply bent channels

In canonical wall-bounded flows, point particle-laden turbulence exhibits a substantial interaction between scales with a variety of regimes, and the dynamics of the point particle-laden fluid are primarily identified by the Reynolds number. Such interactions are even more augmented in curved channels with variable curvature, and fixed Reynolds numbers demonstrate distinct flow behavior, as shown by Brethouwer [J. Fluid Mech. 931, A21 (2022)]. In this work, we demonstrate the characteristics of wall-bounded point particle-laden turbulent flows in sharply bent channels by evaluating the time-averaged velocity profiles at the straight section, at the bend, and in the inclined sections. The mean (time-averaged) normalized velocity profiles retain their well-known logarithmic features, with the von Kármán and additive constants taking different values depending on the acute inclination of the bend. Near-wall fluctuations at the bend are found to be intensified due to the bend that leads to increased turbulent activity. On examining the friction Reynolds number along the bent channel walls in the streamwise direction, a modulated behavior with an abrupt change at the bend is observed. Budgets of turbulent kinetic energy (TKE) are delineated for various inclinations of the bend at different sections of the channel and are compared with the unladen sharply bent turbulent channel flows, which illustrate that TKE is modulated at the bend and there is an overall attenuation of TKE on loading the channel with point particles.

Developing a numerical model for sediment transport in channel network by considering multigrade bed load sediment

ABSTRACT Predicting transport rates is difficult for the morphological features of marine, river, and coastal ecosystems. To design a model bed load sediment transport rate along with the surface layer, a mesh-based numerical method is used, and for the sediment transport the governing equations are employed and depth-averaged is used to create open channel flow and in three-dimensional horizontal space the evaluation is performed. By utilizing the governing equations, the open channel flow discretization and the numerical hydrodynamic model of sediment transport rate are calculated, and in the flow channel by using the solution method the settling velocity is determined. The complex issues involved nonlinear equations for the numerical modelling with solution methodology. The chicken swarm optimization algorithm is revealed by multi-objective metaheuristics optimization, and a better outcome is acquired by optimization. Finally, if polygonal mesh modelling is used in the diversion flow channel and curved bend channel, several experimental models were employed in the model experiments. A numerical measured and improved model is used to estimate the results in comparison, and the optimally developed model forecast rates with accuracy. In some open-channel flows such as reservoirs and rivers, the struggling flow and bed load sediment transport were dealt with in this model. Based on the results obtained, the proposed technique demonstrates significant improvements in both accuracy and prediction performance compared to the existing techniques. The proposed technique achieves an accuracy of 96.87%, outperforming the BCNN technique with an accuracy of 89.77% and the H-ANN-FA technique with an accuracy of 84.65%. Moreover, the proposed technique exhibits a lower RMSE value of 0.12, indicating a substantial reduction in the average deviation between predicted and observed values. Based on the NSE and R2 results, the proposed technique demonstrates remarkable improvements in prediction accuracy compared to the other techniques. The proposed technique achieves an NSE value of 0.998 and R2 value of 0.99, compared to the existing technique with an improvement of 46.47% and 11.24%.

Water purification modeling by functionalized hourglass-shape multilayer nano-channel

In this study, inspired by the overall structure and operation of the aquaporin channel, graphene-based nanochannels are proposed to be used as potential membranes for the water purification process. To this end, an hourglass-shaped channel has been designed using the three-layer porous graphene sheets and the effects of some main channel's elements, such as the channel bending angle and attached functional groups to it, on the filtration performance have been examined by using molecular dynamics simulations. We find that a suitable bending channel shape can improve the channel efficiency, i.e. both the water permeability and the ion rejection rate of the suitable bent channels were more than for the straight channels. In addition, regarding the different functionalized channels, the half-functionalized channels were more efficient than the completed functionalized ones. Furthermore, by monitoring the dynamics of water molecules as they pass through the narrowest part of the channels, it was found that water molecule rotation assists water transport.

Non-unique regimes of oscillatory transonic flow in bent channels

Non-unique regimes of oscillatory transonic flow in bent channels

Numerical Investigation of Bed Shear Stress and Roughness Coefficient Distribution in a Sharp Open Channel Bend

The helical flow leads to the redistribution of the bed shear stress and roughness coefficient in open-channel bends, influencing the transport of sediment and riverbed evolution process. To explore the mechanisms underlying this redistribution, a 3D numerical simulation of a 180° sharp bend was performed by solving the Reynolds-averaged Navier–Stokes (RANS) equations using the Reynolds stress equation model (RSM) as the anisotropic turbulence closure approach. The results indicate that the high bed shear stress zone appeared in the inner bank region from the 50° to 110° sections, and the section maximum bed shear stress gradually shifted outwards, owing to the advective momentum transport by the circulation cells. The quantitative analyses of the terms in depth-averaged Navier-Stokes equations indicate that the contributions of the cross-stream circulation and cross-flow to the downstream bed shear stress were of the same order of magnitude, and the overall contribution rate of the cross-stream circulation was 20%. The contribution rates of the cross-flow, cross-stream circulation, turbulence, and pressure gradient to the transverse bed shear stress were approximately 30%, 7%, 3%, and 60%, respectively, indicating that the pressure gradient term arising from the transverse water surface slope played a dominant role. The Chezy resistance coefficient showed an overall decreasing trend along the bend. Therefore, an effective expression considering the streamwise variation along the centreline and transverse variation was successfully established to predict the uneven distribution of the Chezy resistance coefficient.

Channel Bed Deformation around Double Piers in Tandem Arrangement in an S-Shaped Channel under Ice Cover

Flow structure and channel bed deformation caused by double piers in a tandem arrangement under ice-covered flow conditions in a bent channel is more complicated than those around a single pier in a straight channel. Based on experiments in an S-shaped flume, the scouring phenomenon at double piers in a tandem arrangement under an ice cover has been conducted by varying pier spacing distance, bend apex cross section (BACS), and hydraulic parameters. Results show that, under identical hydraulic conditions, the variation trend of the scour depth in the vicinity of double piers in a tandem arrangement in a bent channel is similar to that in a straight channel. The deepest depth of scour holes at the upstream BACS is more than that at piers at the downstream BACS. At each BACS, the effect resulting from the interaction of double piers gradually decreases with the pier spacing distance. Different from the characteristics of local scour at double piers in a tandem arrangement in the straight flume, when the ratio of pier spacing distance to pier diameter (L/D) is more than 15, the horseshoe vortex generated by the front pier has negligible impact on the rear pier, and the maximum depth of scour hole at the rear pier scour hole is about 90% that of the front pier. Also, when L/D is higher than 15, the influence of the rear pier on the front one is negligible, and the scour hole depth at the front pier remains the same. However, this phenomenon occurs when the straight flume’s L/D is greater than 17.