Rectangular Open Channel Research Articles

Sensitized Reynolds stress modeling of a bubbly jet emerging into a water cross-flow

The present work is concerned with the computational study of an air–water mixture stream emanating from a nozzle submerged in a water cross-flow inside a rectangular open channel to form a curved, intensively dispersed, bubbly jet. The work focuses on evaluating the predictive performance of an eddy-resolving turbulence model applied to the described case of a multiphase gas–liquid flow system characterized by a variety of closely coupled phenomena, including: turbulence anisotropy-induced secondary motion, free surface flow, bubbly jet propagation, and the varying interaction dynamics of the carrier water flow with the air bubble dispersion. Correspondingly, an appropriately extended differential near-wall Reynolds stress model, which describes the dynamics of unresolved subscale structures within the Sensitized Reynolds-Averaged Navier–Stokes (RANS) computational framework, is currently used in conjunction with a two-way coupled Euler–Lagrange approach to simulate this gas-water bubbly flow, with the operating and boundary conditions following the experimental reference of Zhang and Zhu (2013). Accordingly, the conditions at the free surface are adequately derived for all components of the residual turbulence stress tensor and the corresponding length scale determining variable. It is shown that the statistics of the bubble phase can be accurately captured, and the proper-orthogonal-decomposition analysis of the dynamic properties of the flow reveals at least two large-scale transient effects associated with the bubbly jet. Furthermore, in the preliminary part of this work it is shown that the currently applied turbulence model can be successfully used to correctly capture the effects of Reynolds stress anisotropy in the single-phase open-channel configuration, representing the incoming flow field of the main two-phase flow configuration.

Experimental study of simple flumes with converging triangular walls

For water management, the accurate measurement of discharge in irrigation channels is essential. Static flow measuring devices such as weirs and flumes play a significant role in discharge measurement in open channels. Flumes are one of the most commonly used devices for flow measurement. Many researchers have focused on application of simple flumes in irrigation networks. This investigation aims to study the flow discharge through a simple flume with converging triangular walls under free-flow conditions. The flume is constructed by placing two right-angled triangular plates on either side of a rectangular open channel. The channel cross section is rectangular while height of the converging walls reaches to zero at the end of the flume opening. The proposed flume is inexpensive, its operation is simple, its installation is easy and does not require high maintenance (maintenance free). The present study is designed to determine the effect of different variables on flow discharge of this kind of flumes. For this, an experimental program was conducted under upstream subcritical flow regime and under free outflow conditions to formulate the flow discharge of the flume. Flume discharge relationship was deduced using dimensional analysis method and then calibrated using the experimental data collected in this study (318 runs). The proposed discharge equation has an average absolute relative error of 1.66 %, and for 96.5 % of the measured discharge values, the relative errors are within ±5 %. To reliably estimate the flume discharge, free-flow and submerged-flow conditions should be distinguished. For this, suitable equation with an average absolute relative error less than 3.44 % was presented to estimate the submergence threshold. This flume is suitable for the rectangular channel for accurate measurement of free flow at any location on field. This particular device has considerable advantages over the other devices, as it can be quickly installed and removed for use in irrigation channels. The findings and results of this study will be of interest for practical applications.

Numerical research on the wake characteristics and drag reduction of a square cylinder in the presence of control partitions

This study presents the effect of the position of the control partitions on fluid flow around a square cylinder in a rectangular open channel. The numerical simulations are carried out with the lattice Boltzmann method at a fixed Reynolds number (Re=150). In the first case, two downstream partitions are inserted, whose spacing gap (g) varies as a function of the cylinder dimension (d), ranging from 0 to 13d. In the second case, four partitions are implemented such that g is fixed at 3.9d and the upstream spacing varies from 0 to 4d. The numerical results of the first study reveal the existence of a critical spacing at g=3.9d, where the average drag coefficient reaches a minimum (16.28%). Likewise, the vortex shedding between the square cylinder and the two detached partitions or behind these two partitions are also affected. Furthermore, a significant decrease in the drag coefficient, reaching 36.33%, is attained when situating the two upstream partitions at a distance of g1=0.25d.

PERENCANAAN SISTEM JARINGAN DRAINASE DI DESA KARANG DIMA KECAMATAN LABUAN BADAS KABUPATEN SUMBAWA BESAR

Structurally, the drainage in Buin Pandan Hamlet is generally masonry in cement, but due to poor planning, the water flowing on the road and also the planned drainage channel is not in accordance with the water discharge so that water overflows from the drainage channel, which is in Dusun Buin. Pandan, aims to determine whether the current condition of the drainage system is appropriate. After the research has been done, it is known that the value of Cv = 0.485, the value of C_s = 0.026 and C_k = 3.973, it can be concluded that in planning this drainage system the type III log method is used and the rainfall intensity is 0.229 mm/hour in Buin Pandan Hamlet. Then a calculation is carried out with the aim of knowing whether Qr < Qs or Qr > Qs in the drainage in Buin Pandan Hamlet and it is known that the difference between Qr = 5.46 (m^3/s) and Qs = 0.60 (m^3/s) is in the drainage. With steps that can be taken to prevent flooding, namely by re-planning the drainage channel. From the results of the re-planning of the drainage channel, the value of the channel capacity Qs is 5.86 (m^3/s) and the size of the channel that can accommodate water discharge is 1 m wide and 1.60 m high. Channels planned for the same channel, namely open rectangular channels, only have different dimensions.

Preissmann Four-Point Methods for Solution of Simplified Saint-Venant Equations Applied to Flood Routing in Prismatic Open Channels

This research goal to compare the flow properties in the rectangular and trapezoidal open channels by examining the influence of the channel side slope is depicted by simplified Saint Venant Equations. The solution of these equations has been completed numerically by using Preissmann four-point scheme. The model is simulated using the Matlab application to point out the flow properties. The proposed model is validated by the model without simplification which was selected from the literature. The validation outcomes indicate that in common, the simulation outcomes of the two models have a good agreement. The simulation results show that the greater the slope of the channel side, the greater the peak discharge and the greater the time shift. The analysis emphasizes how channel geometry influences flow behavior, indicating that trapezoidal channels, with inclined side slopes z, yield slightly higher peak discharges compared to rectangular ones. For z = 0, discharge of peak Q = 7.38 m3/s and t = 18 s. For z = 2, discharge of peak Q = 7.39 m3/s and t = 21 s. For z = 4, discharge of peak Q = 7.45 m3/s and t = 23 s. For z = 6, discharge of peak Q = 7.51 m3/s and t = 24 s.

Flow structure of the confluence between an open channel and a pipe.

It is common that the sewage is discharged into rivers through a municipal drainage network. The hydraulic properties of the confluence between a lateral drainage pipe and a rectangular open channel are investigated using numerical simulation. The simulation results show that the recirculation zone, the separation area, and the secondary flow are highly influenced by the tailgate height and flow rate ratios. Both the recirculation zone and the separation zone enlarge with the increasing flow rate ratios. The recirculation zone also enlarges with the tailgate height within a certain range. It is worth noting that as the tailgate height increases, two vortices rotating in opposite directions at the same level initially merge into a counter-clockwise rotating vortex, and then one vortex splits into three. Ultimately, one of them dissipates and there are two vortices left on a vertical line. The tailgate can reduce the vertical velocity gradient and the streamwise velocity to moderate the erosion of the channel bed caused by the pipe flow inlet.

Degradation of typical environmental pollutants (ciprofloxacin, carbamazepine and 17-β estradiol) on supported TiO2 photocatalysts: Identification of degradation products and in silico toxicity assessment

The study describes a few significant aspects of photocatalytic studies: (i) the methodology for finding optimal support for TiO2 photocatalytic films with possible environmental application and (ii) degradation of pollutants of widespread concern including detailed kinetic study and identification of degradation products with respective in silico toxicity assessment. Different cotton textiles and glass fiber mesh were studied as flexible supports for TiO2. Preliminary experiments were done with an aqueous solution of 2-HBA in a rectangular open channel reactor under UVA light, due to known kinetics and photocatalytic degradation pathway of 2-HBA. Further environmental application of the photocatalytic film on the most appropriate support was studied in the same reactor using ciprofloxacin (CIPRO), carbamazepine (CARBA) and 17β-estradiol (E2) as model environmental pollutants under UVA and artificial solar irradiation. A detailed kinetic study, including photon absorption effects, was performed using recently published models. Degradation products were identified by means of high-resolution mass spectrometry (UHPLC-QTOF MS system) with electrospray ionization analysis of the water samples. The environmental impact of photocatalytic oxidation of CIPRO, CARBA and E2 was addressed via in silico toxicity assessment of initial pollutants and respective degradation products.

Semi-analytical method to estimate boundary shear stress in smooth rectangular and trapezoidal open channels

The boundary shear stress is obtained from the continuity and momentum equations in smooth prismatic open channels. Shear stress is a function of gravity, secondary flow, and gradient velocity. In this research, semi-analytical equations were obtained to estimate the average boundary shear stress in smooth rectangular and trapezoidal open channels by 0.5, 1, 1.5 and 2 side slopes using conformal mapping techniques. After dividing the channel cross section into the bed and wall sub-sections, the present study used the method by Guo and Julien (2005) to estimate the average shear stress of the bed and the wall in open channels. For the studied case, by the first shear stress estimation, secondary current and constant eddy viscosity were neglected. After recommending two secondary current and eddy viscosity correction factors, a second approximation well matched the experimental measurements of the average shear stress for all aspect ratios.

Flow Control in a Rectangular Open Channel using Two Impermeable Spur Dikes: A Numerical Study

The present study examines how adjusting vegetation patches in a rectangular open channel with two impermeable spur dikes alters the displacement of the recirculation region. The Reynolds stress turbulence model is implemented via the 3D numerical code FLUENT (ANSYS). Mean stream-wise velocity profiles were drawn at selected positions and at mid of flow depth i.e., 3.5 cm, a horizontal plane is cut through the open channel for analyzing velocity contours and streamline flow. The findings indicate that the stream-wise velocity profiles showed fluctuations in the presence of different shapes and arrangement of cylindrical patch discussed and the maximum velocity within the field of spur dike is of the order of 0.018 m/s due to the prism shape. By changing the position of the cylindrical patch, the location of the recirculation region displaces within the field of impermeable spur dike.

A partitioned model for predicting the spatial development of flow in ecological vegetated rivers with submerged vegetation

The evolution of the velocity caused by submerged vegetation in river courses with regular cross sections has been poorly investigated using analytical methods. Fully understanding the longitudinal profiles of the velocity is significant and essential to study the hydrodynamic processes taking place in wetland ecosystems, which is the most important indicator of energy transfer and material exchange in fluvial ecosystems. Based on the experimental data in the literature, the streamwise velocity gradually is found to decrease in the submerged vegetation and increase in the free surface layer. A four-panel analytical model derived from exponential decay theory was developed to predict the streamwise velocity occurring both upstream and within vegetation along the main flow direction in a rectangular open channel with a submerged vegetation patch. We aim at the development of velocity, which is averaged across the vegetation and free surface layers separately, and the length scales shown in the velocity evolution. The explicit calculation expression for each parameter in the analytical model was provided, and sensitivity analysis was conducted by changing the parameters to check how the predicted velocity changed. The change in the drag coefficient of vegetation (CD) and the velocity at the leading edge of the vegetation (U0) influenced the development of velocity. The former mainly enlarges the velocity difference between the vegetation and free surface layers after the leading edge as it increases, and the latter mainly diminishes the velocity difference before the leading edge as it increases. The error statistics is conducted and shows that the predicted and measured velocities are consistent within a relative error of 11%, indicating that the partitioned model is applicable in predicting longitudinal velocity in flows with submerged vegetation of various flexibility. The theoretical analysis of velocity development paves the way for the future studies on the flow turbulent structure and sediment transport in partially vegetated rivers.

THE INFLUENCE OF THE CHANNEL BED RECTANGULAR CONFIGURATION ON SEDIMENT TRANSPORTATION

Sediment transport is the movement of organic and inorganic particles caused by gravity, a moving fluid’s force, the wind, and ice motion. Sediment deposition degrades dams’ safety, leading to environmental pollution and channel area reduction. This study describes the effect of the weir height and spacing of used and non-used rectangular configuration structures on sediment transport rates in an open channel. This project was created using a rectangular open channel (30 cm wide and 60 cm deep). A sharp-crested weir was installed in the channel, and the rectangular wooden configurations were fixed in specific locations on each weir to reduce the bedload transportation rate and sediment motion. The weir heights were different (0.25B, 0.35B, 0.45B, and 0.55B, where B is the channel width). Also, the spacing between the baffle blocks (S) was set to 4Y, 8Y, 12Y, and 16Y, where Y was the maximum water depth without installing blocks and weirs. The results showed that the maximum transported bedload for the lowest weir was 1.4 kg/min, but only 4.4 × 10-3 kg/min was transported for the weir 16.5-cm high with baffle blocks. Using long baffle blocks yielded a worse result than using no blocks. The sediment-transport rate increased to 1.66 kg/min for the 7.5-cm weir due to block configurations. In conclusion, the obtained result contradicts the predicted result, as using baffle blocks increased the sediment transportation rate.

Experimental and Numerical (Fluent-VOF, k-ϵ, DPM) Study of Variation of Trap Efficiency of Irregular Hexagonal SIT (Sediment Invert Trap) for Particle Removal in Rectangular Open Drains and Sewers

At some locations along the length of open sewers and drains, sediment particles get deposited on the bottom bed, reducing hydraulic efficiency. A sediment invert trap (SIT) can be implemented on the bottom of open sewers and drains to trap sediment particles moving on the bed surface. Several investigators have conducted experimental and computational studies to understand the particle trapping behavior of invert traps of various shapes and depths under varying sediment and flow parameters. In experimental studies, previous investigators have used actual and artificial sediment particles; in computational analyses, spherical particles have been considered. The current study investigated the particle trapping behavior of an irregular hexagonal sediment invert trap (SIT) through experiments and two-dimensional (2D) numerical modeling. Seventy-two experiments were performed using actual sewage solid particles in an open rectangular channel with a bottom-fitted invert trap with multiple depths. Sixty numerical simulations were performed using ANSYS Fluent 2020 R1 computational fluid dynamics (CFD) software, considering spherical and nonspherical sewage solid particles. The velocity field was predicted using the volume of fluid (VOF) model combined with the realizable k-ϵ turbulence model. Particle trap efficiency was predicted using a stochastic discrete phase model (DPM). Trap efficiency varied significantly with depth of flow, invert trap depth, slot aperture size, and particle size and shape. Analysis of the simulated flow field showed that variation of turbulent kinetic energy above the trap’s slot aperture was also responsible for variations in trap efficiency values. Fluent simulations considering particles as nonspherical (using shape factors) agreed well with experimentally measured trap efficiency, with mean absolute percentage errors (MAPE) of 6.23%, 8.79%, and 13.77% for particle size ranges SS1, SS2, and SS3, respectively, with both slot apertures at all flow depths. The 2D-CFD study consistently overpredicted trap efficiencies compared to the experimental findings. With a fixed length and width of 0.32 and 0.15 m, respectively, the optimal depth of the irregular hexagonal SIT was found to be 0.65 m with slot aperture sizes of 0.15 and 0.03 m, whereas with slot aperture size of 0.15 m only, invert trap depths equal to 0.58, 0.43, and 0.38 m was found as optimum.

Experimental study of simple flumes with trapezoidal contraction

There are different devices available for measuring the flow discharge. Static measuring devices such as weirs and flumes (without any moving parts) play a significant role in discharge measurement in open channels. Many researchers have focused on application of flumes in irrigation networks. This investigation set out to study the flow discharge through a trapezoidal cut-throated flume (TCTF). The flume is simply constructed by placing two triangular plates on either side of a rectangular open channel to form a trapezoidal throat. The channel cross section is rectangular while throat cross section of the flume is trapezoidal. The proposed flume is simple, low-cost, easy to install and does not require high maintenance. The present study was designed to determine the effect of different variables on the flume discharge. For this, an experimental study was carried out under free outflow conditions and under upstream subcritical flow regime to formulate the flume discharge. Three models are defined for flume discharge relation based on the Buckingham's theorem of dimensional analysis, and then calibrated using the experimental data collected during this study. The first discharge model has an average error of 1.81%, while the second and third improved models have average errors of 0.96% and 1.44% respectively. To reliably estimate the flume discharge, free-flow and submerged-flow conditions should be distinguished. For this, suitable equations with an average error less than 2.23% were presented to estimate the submergence threshold. The results of this study indicate that while the downstream wall slope influences the submergence threshold, the flume discharge is not influenced by this variable. The proposed models are simple and accurate and present appropriate estimation of discharge for flows through the TCTFs. The findings of this study will be of interest for practical hydraulic engineers.

Promotive Effects of Siltfence on Deposition of Suspended Particles: Evaluations of Diffusion Suppression of Radionuclides in Rectangular Open Channel via Numerical Simulations

A siltfence is installed to prevent the spread of suspended sediments generated by engineering construction works in rivers and on the coast. Thus, the siltfence is regarded to be a tool to prevent radioactive materials adsorbed on suspended sediments from diffusing into the sea in ports of nuclear power plants during nuclear accidents. However, the prevention effects of the siltfence as sediment control structures have not yet been fully evaluated. Therefore, in this paper, we simulate the behaviors of suspended sediment particles using a coupled simulation scheme composed of water flow and deformation of the siltfence in a rectangular open channel under uniform steady flow, and evaluate the promotive effects of the installed siltfence on suspended sediment deposition. The results demonstrate that the installation of the siltfence significantly promotes deposition, especially of particles with low settling velocities. However, it should be noted that the opposite case is also possible, i.e., the siltfence promotes the diffusion of suspended sediments under particular conditions. These results suggest that a careful installation strategy is necessary. The present simulation scheme is useful in assessing the prevention effects of siltfences prior to their installation.

Discharge coefficient relationship for the sharp-edged width constriction new theory and experiment

In the field of flow measurement, what is needed in general rule is to design devices that are inexpensive, fairly accurate, and easy to implement. Some devices are more accurate than others but are very expensive.The present study examines a device for measuring flow in rectangular open channels that combines the three abovementioned advantages. It is made up of two separate vertical thin plates arranged in such a way that they form a central opening of width b less than the rectangular channel width B in which they are inserted. It is the simplest device ever imagined and designed for flow measurement in open channels.It is planned to derive the stage-discharge relationship by borrowing a rigorous theoretical development based on classical hydraulic formulas, accounting for the effect of the approach flow velocity. The intended stage-discharge relationship will allow us to derive the resulting discharge coefficient equation of the device.It is established that the resulting theoretical discharge coefficient is formally identified as being exclusively dependent on the contraction rate β = b/B, and this finding is predicted by dimensional analysis. Both dimensional and experimental analyses show no effect of the upstream water depth on the discharge coefficient for the selected values of β. The derived theoretical discharge coefficient relationship is straightforward, although it contains trigonometric functions that are somewhat cumbersome when the designer needs to perform a rapid field calculation.The theoretical and mean-experimental discharge coefficients of the eight tested devices are carefully compared using the one hundred and fifty-seven experimental values collected. An excellent agreement, even perfect, is observed since the maximum deviation worked out over the tested range of β is only 0.05%. This confirmed the validity of the theoretical relationship governing the discharge coefficient, which does not need any correction.

An investigation of induced free-surface wave oscillations in prismatic open-channel

ABSTRACT This paper reported on the free-surface wave behavior in a rectangular open-channel, induced by sluice-gate maneuvers. Numerical computations used the McCormack scheme to solve the one-dimensional extended St-Venant model embedding the Prandtl power-law momentum correction coefficient. The fundamental pulsation of the hydraulic system was inspected using the analogy with the water-hammer theory, known in pressurized-pipe flows. Different flow scenarios were reported; including the superposition between (i) downstream water-hammer maneuver and sine excitation of upstream flow depth and (ii) sinusoidal fluctuations of upstream lateral inflow and downstream flow-depth. Results highlighted that such sluice-gates maneuvers involved severe scenarios leading to significant amplifications of the depth peak and crest values above the initial value.

Developing a Lagrangian sediment transport model for open channel flows

A three-dimensional stochastic Lagrangian particle tracking sediment transport model is developed to solve the discrete advection–dispersion equation using a combination of empirical dispersion equations. The performance of three widely-used longitudinal dispersion coefficient equations was examined to select one of them as the primary dispersion equation term in the developed model. Also, a conditional empirical equation was used to consider the effect of vertical dispersion term in top layers near the water surface. The performance of particle tracking model (PTM) to calculate the sediment concentration was evaluated for various sediment classes (very fine sand, fine sand, and medium sand) using available laboratory dataset. Multiple statistical measures were calculated using the Taylor diagram for each dispersion equation. Based on the result, the developed particle tracking model estimated the suspended sediment concentration in a rectangular open channel with a correlation coefficient (R) of 0.96, standard deviation (STD) of 0.262, and root mean square deviation (RMSD) of 0.06 for three different sediment classes proving the acceptable accuracy of the developed model for different range of sediment gradations. In addition, the accuracy of PTM was compared to recently developed models. Comparison between the particle tracking model and the analytical solution of the advection–dispersion equation showed that the developed model predicted the maximum concentration of suspended sediment 6% and 9.4% lower than the analytical solution result for 30 and 50 s simulation time in the straight channel, respectively. However, there was a good agreement between the longitudinal and transverse sediment concentration distribution from the model and the analytical solution approach. The result of the sensitivity analysis and validation process showed that the model could be used to simulate sediment transport in open channel flows.

Energizing Process for Levitating the Boat Vehicle Attached with Air Vessels at Static Conditions: A Novel Method of Waterway Transportation

Levitation generally refers to the force that resists gravitational force in any particular direction. This article postulates an experimental setup that is used to describe the application of hydrostatic force for developing a new mode of hovering-based levitation system. This research work explores how a new hovering process can be created with the help of a water vehicle attached to the air vessels. With this hovering process, it is likely to test that the lateral force of the water acts on the bottom of the boat vehicle and creates a new levitation system. By minimizing the resistance forces such as rolling, aerodynamic and skin friction resistances, it is possible to ensure that new modes of transportation systems such as Maglev and Hyperloop were introduced. The relationship between the amount of water in the open rectangular channel, the draft value of the boat vehicle, the volume of air vessels attached and the payload is estimated. In both boat vehicle models with and without air vessels, changes in buoyancy, changes in draft value and changes in the momentum of the water beneath the vessel are experimentally tested and compared. This comparative study confirms the formation of levitation on a boat vehicle to which air vessels are attached. Thus, with a boat model attached to the open-bottomed air vessels, the hovering process is tested and demonstrated how much the levitating force developed at static conditions. In the future, this method can be used as a low-cost levitation method in the transportation sector.

FEATURES OF THE APPLICATION OF THE BUNEMANN ALGORITHM FOR NUMERICAL SOLUTION OF THE THREE-DIMENSIONAL PROBLEM OF MOTION OF A VISCOUS LIQUID IN AN OPEN CHANNEL

The article deals with a three-dimensional turbulent model of the flow of a viscous liquid in an open rectangular channel. On the free surface, the condition of friction in the longitudinal direction is taken into account, on and near the wall of the channel the conditions are set: adhesion, laminar and turbulent layers, and along the longitudinal axis of the flow - the condition of periodicity. To solve the problem, a cosine-shaped spectral function by vertical coordinate and a predictor-corrector scheme of the method of fractional steps by horizontal coordinates are used. For isoperimetric data, the corrector scheme uses the Buneman algorithm, which is particularly complex.

Supercritical Flow over a Submerged Vertical Negative Step

The transition from supercritical to subcritical flow around a fully submerged abrupt negative step in a horizontal rectangular open channel has been investigated. In a laboratory experiment the one-dimensional energy and the momentum conservation equations were studied by means of depth and pressure measurements by piezometers installed along the bottom and the step face. Froude number varied in the range 1.9 to 5.8 while the step height to critical depth ratio was in the range 1.34 to 2.56. The results are presented in dimensionless form using mainly a characteristic length scale that is the sum of critical depth and step height and the Froude number of the supercritical flow upstream. Five different types of rapidly varying flow are observed when the subcritical downstream tailwater depth varied. The supercritical water jet at the top of the step either strikes the bottom downstream of the step when the maximum pressure head is greater, or moves to the surface of the flow when it is lower than tailwater depth, and the separation of the two flow regimes occurs when the tailwater depth to the characteristic length scale is around 1.05. The normalized energy loss and a closure parameter for the momentum equation are presented in dimensionless diagrams for practical use by the design engineer. Finally, the one-dimensional equations of motion including Boussinesq terms are solved numerically and the results found are congruent to the experimental findings.