Submerged Flow Conditions Research Articles

Application of SVM, ANN, GRNN, RF, GP and RT models for predicting discharge coefficients of oblique sluice gates using experimental data

AbstractGates are commonly used to adjust water flow in open channels. By using an oblique/inclined gate, the water transferring capacity of open irrigation canals can be increased. Investigation of free and submerged discharge coefficients for inclined sluice gates is the focus of the present study. First an experimental apparatus incorporating an inclined gate was created. The inclined angle (β) and gate opening (a) were experiment variables, and the five inclination angles include: 0° (vertical gate), 15°, 30°, 45° and 60°. Experimental results showed a greater convergence of flow lines under the gate and increasing the gate angle causes the discharge coefficient to increase. Also experiments showed that increasing the submergence rate (yt/a), decreases the inclined gate discharge coefficient. Performance metrics were created for the experimental results. The metrics utilized Gaussian process (GP) regression, support vector machine (SVM), artificial neural networks (ANN), generalized regression neural network (GRNN), random forest (RF) regression and random tree (RT) based models which were used to predict discharge coefficients (Cd) in both submerged and free flow conditions. The model input parameters were the ratio of the upstream water depth to gate opening (y/a) and the inclined angle (β) for free flow and also the submergence rate (yt/a) for submerged flow. The prediction models show that the ANN model in free flow conditions has the following performance metrics: Coefficient of determination, R2= 0.9957, Root Mean Square Error (RMSE) = 0.0044, and Mean Absolute Error (MAE) = 0.0017. The performance metrics for submerged flow conditions were R2 = 0.9922, RMSE = 0.0079 and MAE = 0.0054. The ANN approach is the most accurate model compared to the others.

The effect of the obstacle on the hydraulic response of the composite hydraulic structure

Experimental investigations are carried out to study the physics of the flow that passes weir-gate hydraulic structure and encounters obstruction with or without installation of downstream opening. This study approaches the comparison between two different options; the first option deals with free flow condition while the second option deals with submerged flow condition. Various cases are performed considering different hydraulics variables and dimensions variables to evaluate the existence of obstruction with or without openings. Overall the flow pattern is more sensitive to the presence of obstruction at downstream region than in its absence. The hydraulic variables that are considered in the study are divided into dimensional variables such as discharge, downstream flow velocity and water depths at downstream and non-dimensional variables such as discharge coefficient, Froude number and Reynolds number. The obstacles which are used in this study have variable heights with constant width and length. Constant spacing between the obstacles is adopted. Different arrangements of obstacles are considered in this study and it is found that a significant and reasonable result is different among the cases. The effect of rectangular opening in the obstruction on flow pattern is studied. The effect of obstacles with rectangular opening gives a noticeable result in the assessment of the discharge coefficient of the composite hydraulic structure.

Hydraulics of sharp-crested weir culverts with downstream ramps in free-flow, partially, and fully submerged-flow conditions

Laboratory experiments were conducted to investigate the hydraulics and discharge characteristics of sharp-crested weir culverts with downstream ramps for hydraulically smooth wall boundary and for free, partially submerged, and fully submerged-flow conditions. Four weir-culvert models were tested with different weir heights, ramp lengths, and culvert heights. The partially submerged-flow conditions were created when a slight increase in tailwater caused the headwater to rise due to partial submergence of the culvert. In this flow regime, supercritical flow over the ramp interacted with culvert outflow and this flow regime was classified as Supercritical Jet Interaction Regime or SJIR. Once tailwater reached the weir crest, the weir flow regime became submerged indicating fully submerged-flow condition. Based on the variations of water surface profiles, submerged flows were further classified into Surface Jump Regime (SJR), Surface Wave Regime (SWR), and Deeply Submerged Regime (DSR) and the boundaries between each flow regime were defined by regime plots. To predict discharge of weir culverts with downstream ramps, variations of discharge coefficient with weir geometry and flow regimes were studied and empirical formulations were developed. In addition, free and partially submerged flow discharges were predicted by implementing the interaction factor. It was found that the interaction factor was independent of the Froude number in SJR, while it correlated with the Froude number in SJIR. Under submerged-flow conditions, evaluation of the discharge characteristics of the proposed weir-culvert model showed correlations with water surface flow regimes and a three-stage prediction formula was proposed for estimation of submerged flow. The energy losses over weir-culvert models were also calculated and it decreased with submergence.

Experimental study on free and submerged multi-jets

The flow characteristics of the hydraulic jump due to parallel jets are different from the classical jump emerging from a single gate. Due to the highly complex flow field at the downstream pool, deciding about the tailwater measuring location is a challenging issue affecting the flow measuring accuracy. Experiments are conducted herein, on different parallel jets’ configurations for both free and submerged flow conditions. To quantify the flow uniformity, for any downstream cross section, the associated momentum correction factors, β2, were estimated for the free-flow condition. It is found that β2-values depend significantly on the measuring location, and consequently the available conjugated depths relationship results in poor estimation when measuring location moves downstream. Employing Buckingham analysis, a general formula is proposed to calculate the momentum correction factors associated with the free hydraulic jump at different downstream measuring locations. The experimental results of this study indicated that such a formula enhances distinguishing between free and submerged flow conditions of the gates installed in parallel. Finally, a dimensionless stage-discharge formula is presented to predict the submerged flow rate through parallel gates of different gate openings and widths.

Energy Dissipation and Hydraulics of Flow over Trapezoidal–Triangular Labyrinth Weirs

In this work experimental and numerical investigations were carried out to study the influence of the geometric parameters of trapezoidal–triangular labyrinth weirs (TTLW) on the discharge coefficient, energy dissipation, and downstream flow regime, considering two different orientations in labyrinth weir position respective to the reservoir discharge channel. To simulate the free flow surface, the volume of fluid (VOF) method, and the Renormalization Group (RNG) k-ε model turbulence were adopted in the FLOW-3D software. The flow over the labyrinth weir (in both orientations) is simulated as a steady-state flow, and the discharge coefficient is validated with experimental data. The results highlighted that the numerical model shows proper coordination with experimental results and also the discharge coefficient decreases by decreasing the sidewall angle due to the collision of the falling jets for the high value of H/P (H: the hydraulic head, P: the weir height). Hydraulics of flow over TTLW has free flow conditions in low discharge and submerged flow conditions in high discharge. TTLW approximately dissipates the maximum amount of energy due to the collision of nappes in the upstream apexes and to the circulating flow in the pool generated behind the nappes; moreover, an increase in sidewall angle and weir height leads to reduced energy. The energy dissipation of TTLW is largest compared to vertical drop and has the least possible value of residual energy as flow increases.

Hydraulic performance of elliptical-LOPAC gate under submerged flow conditions

This study intended to investigate the hydraulic performance of the new types of LOPAC gates, namely the elliptical LOPAC (EL) gate, and the rectangular LOPAC (RL) gate for irrigation canals. To that end, 90 experiments were carried out at three different flow discharges (25, 35, and 45 l/s), three different submergence ratios (y2/y1 = 0.7, 0.8, and 0.9) and five different gate opening angles (35, 40, 45, 50, and 52.5°). In the EL gate, as the submergence ratio decreased by 20%, the maximum increase in Cd for the discharges of 25, 35, 45 l/s at 52.5° of gate opening angles happened in the order of 0.426, 0.475, and 0.506, respectively. Moreover, the maximum decrease ratios in ΔE/E1 followed by 20% increase in the submergence ratio for the same discharges at 35° of gate opening angles were 0.195, 0.1944, and 0.1922 respectively. Finally, the empirical rating curve and equations were proposed to predict Cd and ΔE/E1 for both the EL and RL gate models. For the EL gate, the RMSE ratios for the proposed Cd and ΔE/E1 equations were obtained 0.0027 and 0.0021 respectively.

Diversion of Flow and Sediment Toward a Side Channel Separated From a River by a Longitudinal Training Dam

AbstractA human‐made entrance to a side channel separated from the river by a longitudinal training dam can be considered a new, emergent type of river bifurcation. To understand the processes controlling the diversion of flow and sediment toward the side channel at such bifurcations, a comprehensive field monitoring program was performed in the Waal River, which is the main branch of the Rhine River in the Netherlands. Local processes govern the flow field in the bifurcation region. The angle between the main river flow and the flow into the side channel increases with decreasing lateral and longitudinal distance to the bifurcation point, which corresponds to the head of the training dam. The general flow pattern can be well reproduced with a uniform depth, potential flow model consisting of a superposition of main channel flow and lateral outflow. For submerged flow conditions over the sill, the side channel hydraulic conditions influence the exchange processes, yet free flow side weir theory describes the flow field at this bifurcation type qualitatively well. The vertical flow structure in the side channel, which governs the sediment exchange between the main channel and the side channel, is steered by the geometrical details of the sill. The presence of the sill structure is key to controlling the morphological stability of this type of bifurcation given its primary influence on bed load sediment import and exerts an indirect impact on suspended sediment exchange.

Karakteristik Kecepatan Aliran Di Dekat Dasar Pintu Peluapan Bawah (Sluice Gate)

Pintu air berfungsi sebagai pengatur aliran air yang berfungsi untuk mengendalikan debit, muka air dan monitoring debit. Aliran air yang mengalir melalui pintu dapat dalam kondisi aliran bebas maupun aliran terendam yang tergantung dari kedalaman tailwater . Karakteristik aliran yang mengalir melalui pintu air berdasarkan persamaan keseimbangan energi dan momentum, yang tergantung dari tekanan, kecepatan dan kedalaman air yang berada di hulu /hilir pintu air. Hidrolika pintu air terutama pada kondisi aliran bebas sangat dinamis, termasuk profil muka air, gaya yang terjadi pada pintu, atau distribusi pintu bagian bawah, yang banyak diabaikan. Terdapat beberapa pengembangan rumus dasar dari aliran yang mengalir melalui pintu air, terutama pada pengembangan vena kontrakta. Vena kontrakta akan menghasilkan nilai dari koefisein debit ( C d ) dan koefisien kontraksi ( C c ) yang didapatkan dari rasio perhitungan metode yang sudah ada. Metode dapat juga dengan rasio pengukuran, perhitungan kejadian secara teoritis dan melalui percobaan di laboratorium. Persamaan debit melalui pintu tidak terlalu efektif bila digunakan pada kondisi bukaan pintu yang besar dan pada kondisi pintu terendam penuh.

Experimental Investigation of One-Cycle Triangular Labyrinth Weirs with an Upstream Pool

AbstractThe hydraulic performance of triangular labyrinth weirs with an upstream pool was experimentally studied in both free and submerged flow conditions. The discharge coefficients based on chan...

Discharge characteristics and structure of flow in labyrinth weirs with a downstream pool

A new design of a labyrinth weir is introduced in this study by adding a square pool to the vertex of a one-cycle triangular labyrinth weir with a sidewall angle of 45°. The addition of the square pool increased weir length without causing an excessive nappe interaction, and as a result, reduced the head water over the weir with the same discharge. Laboratory experiments were carried out to investigate the hydraulic performance of the new design with a potential application in pool-weir fishways. Mean and turbulence characteristics of flow for different weir geometries and in both free and submerged flow regimes were measured to be used for prediction of fish behaviour in the upstream of the proposed weir models. Discharge coefficients based on channel width and weir length were calculated. It was found that the new design can significantly increase the capacity of triangular labyrinth weirs and provide financial advantages in construction over triangular labyrinth weirs without pools in low discharges. In submerged flow conditions, the proposed model performed better than sharp-crested linear weirs in low discharges. Contour plots of the three-dimensional velocity components showed a region of strong mean flow around the neck of the new weir model. Turbulent characteristics such as turbulent kinetic energy, power spectra, exuberance ratio, and joint probability distribution functions of velocity fluctuations were extracted from instantaneous three dimensional velocities for different weir depths and flow regimes. Two vertical planes were identified based on the highest turbulent mixing in free and submerged flow regimes. The depths contributing the most to turbulent mixing were identified; active depths decreased as the flow regime changed from free to submerge flow regime.

Robust Fractional Order Control of a Pool of a Main Irrigation Canal in Submerged Flow Condition

This work addresses the robust control of a pool of a main irrigation canal working in a submerged flow condition. A laboratory prototype of hydraulic canal at the University of Castilla-La Mancha is used in this study. A series connection of a non-linear static block and a linear first order plus time delay system is proposed to model the dynamics of such process for all the considered operating regimes. The gain variations in function of the operating regimes are counted and corrected by using a gain scheduling block that inverts the before nonlinearity. However, a residual gain variation remains, whose effect is corrected by a fractional-order proportional integral PI controller that is robust to process gain changes. Such controller is tuned to make the closed-loop system fulfill two temporal specifications: (a) a desired overshoot, obtained defining an equivalent phase margin frequency specification and (b) a desired settling time, obtained defining an equivalent gain crossover frequency specification. Moreover, a third specification is defined: the isophase margin condition, which accounts for the changes in the gain. The simulated results of our canal show the adequate performance of this control system.

Submergence coefficient of full-width sharp-edged broad-crested rectangular weirs

Abstract Full-width sharp-edged broad-crested rectangular weirs in the range 0.1 < h/L ≤ 0.3 situated in rectangular channels are frequently used in submerged flow conditions. To determine the discharge for the submerged flow, submergence coefficient and modular limit shall be known. This article deals with their determination upon a theoretic derivation and experimental research. The equation for modular limit has been determined from energy balance with simplifications. To validate it, extensive experimental research was carried out. However, the derived equation is too complicated for practical use which is why it was approximated by a simple equation applicable for the limited range. The equation for submergence coefficient was derived by modifying Villemonte’s application of the principle of superposition and its coefficients were determined using the data from experimental research of many authors. The new system of equations computes the discharge more accurately than other authors’ equations, with the error of approximately ±10% in full range of the measured data.

Experimental investigation of the effect of skew angle on partially or fully submerged deck scour

This paper presents the results of an experimental study investigating the effect of skew angle on clear-water contraction scour under a bridge deck at partially and fully submerged flow conditions. Two bridge deck models without a pier, one of which was located perpendicular to the flow while the other one was located with skewness of 15°, were used in the study. Forty experiments were performed for each deck model, 24 of which were under partially submerged and 16 were under fully submerged flow conditions. Analysis of the experimental data showed that as the discharge and approach flow depth increased, the maximum scour hole depth under the skewed deck model increased up to 25%–66% for fully submerged flow and 17%–57% for partially submerged flow conditions. Furthermore, the effect of skew angle significantly enlarged the width of the scour hole as you move along the skewed deck.

New stage-discharge relationship for cylindrical and semi-cylindrical edged sluice gates

Gates are simple hydraulic structures which have been widely used for flow control and measurement in irrigation networks. In this paper new sluice gates with cylindrical and semi-cylindrical edges were introduced and the flow movement below these types of gates was experimentally investigated for both free- and submerged-flow conditions. The Buckingham theorem of dimensional analysis and the self-similarity theory were applied for developing the stage-discharge relationships for the two investigated flow conditions. For these cylindrical and semi-cylindrical edged gates and a free-flow condition, the proposed stage-discharge relationship was characterized by an estimate error less than or equal to 5% for 96.0% and 93.7% of the calculated values, respectively. Finally, an equation for calculating the maximum tail water depth allowing free flow condition was proposed.

Mean velocity and turbulent characteristics of flow over half-cycle cosine sharp-crested weirs

The classical sharp-crested weirs are not suitable to implement in irrigation canals with high suspended sediment flow. Over the time, sediment deposition occurs in the upstream of sharp-crested weirs and causes a time variant water level raise in the upstream and consequently variable discharge coefficients. A series of laboratory experiments was carried out to test the hypothesis of strong turbulent formation and three-dimensional flow in the upstream of half-cosine sharp-crested weirs to prevent sediment deposition. To verify this hypothesis, a series of laboratory experiment was carried out for different weir heights and top widths in free and submerged flow conditions. Mean flow structure and turbulent characteristics of half-cosine and rectangular sharp-crested weirs were measured using a micro-Acoustic Doppler Velocimeter (ADV) probe. It was found that the streamwise velocities of half-cosine weirs were higher than the corresponding rectangular weirs, however, the velocity fluctuations in this direction were similar for both types of weirs. Velocity fluctuations in vertical and transverse directions were found to be significant in half-cosine weirs. The results showed higher turbulent kinetic energy below the crest level for half-cosine weirs which made them capable of sediment resuspension and sediment removal. In was found that the introduced weir model are suitable structures for passage of small floating debris and sediments. A head-discharge formulation was also developed based on the geometry of half-cosine weir in free flow and a constant discharge coefficient was obtained by solving the Fresnel integrals. For practical purposes, semi-empirical formulations were also developed to estimate flow discharge in both free and submerged flow conditions.

Hydraulics of flow over rectangular labyrinth weirs

Laboratory experiments were carried out to study the hydraulics of flow over rectangular labyrinth weirs in both free and submerged flow conditions. In order to study the effects of approach velocity and rectangular pool dimensions, nine weir models with different pool lengths a, widths b, and discharge were tested. The length-to-width aspect ratio a/b was varied from 0.25 to 3. The discharge coefficients of rectangular labyrinth weirs were compared with the discharge coefficients of linear sharp-crested weirs of the same channel width B and weir height P. It was found that the discharge coefficients decreased with increasing the approach velocity and the pool aspect ratio. Semi-empirical formulations were developed to predict the discharge over rectangular labyrinth weirs in free flow condition. A critical approach velocity was introduced to evaluate the advantages of the rectangular labyrinth weirs over sharp-crested weirs. It was found that rectangular labyrinth weirs are hydraulically more efficient than sharp-crested weirs for ho/P ≤ 0.4 where ho is the water head over the crest of the weir in free flow condition. Performance of rectangular labyrinth weirs in submerged flow condition were investigated. Experimental data indicated that rectangular labyrinth weirs are more sensitive than the linear sharp-crested weirs in submerged flow condition. Having the same headwater in submerged flow condition, flow over rectangular labyrinth were 10% and 20% less than linear sharp-crested weirs for pool aspect ratios of a/b ≥ 1 and a/b < 1, respectively.

Experimental determination of contraction coefficient and velocity coefficient for radial gates with elliptical lips

Radial gates are widely used to control the flow in irrigation channels and spillways. Radial gates require lower hoisting force and have better discharge characteristics in partial gate openings. The accurate discharge measurement through a radial gate is a challenging problem especially in submerged flow conditions. The coefficient of contraction $$ C_{c} $$ is an important parameter for accurate discharge measurement in open channels. In this study, an attempt has been made to determine the coefficient of contraction $$ C_{c} $$ and velocity coefficient $$ C_{v} $$ for radial gates both for free flow and submerged flow conditions. The flow emanating from a gate is similar to the wall jet emerging from a nozzle. The $$ C_{c} $$ and $$ C_{v} $$ values under free and submerged flow conditions are obtained from the measured jet velocity and the discharge. The coefficient of discharge values under submerged flow conditions show large variations with submergence and hence discharge characteristics needs to be improved for better control of flow. Hence, experiments are conducted so as to improve the discharge characteristics by modifying the exit geometry of the radial gate by attaching a quarter of an elliptical lip. Three different geometries of elliptical lips were attempted and the results show reasonable increase in the contraction coefficient.

Discussion of “Extraction of the Flow Rate Equation under Free and Submerged Flow Conditions in Pivot Weirs with Different Side Contractions” by N. Sheikh Rezazadeh Nikou, M. J. Monem, and K. Safavi

Discussion of “Extraction of the Flow Rate Equation under Free and Submerged Flow Conditions in Pivot Weirs with Different Side Contractions” by N. Sheikh Rezazadeh Nikou, M. J. Monem, and K. Safavi

Flow regimes at grid drop-type dissipators caused by changes in tail-water depth

ABSTRACTA comprehensive set of experiments was performed on grid drop-type dissipators in a rectangular open channel. The study aims to examine the adjustment and boundaries of different flow regimes as well as the variation of flow hydraulic characteristics downstream of a grid drop-type dissipator, caused by the gradual alteration of the tail-water depth. Considering an upstream subcritical flow approaching the grid drop-type dissipator, the tail-water depths were gradually changed until they exceeded the height of the vertical drop leading to a submerged flow condition. The flow regimes and hydraulic characteristics of the flow downstream of the drop were precisely inspected using flow visualization techniques. Results indicated that two key flow regimes, namely “bubble impinging jet flow regime” and “surface flow regime”, arise because of the changes made in the tail-water depth. Accordingly, empirical equations were derived for estimating the boundaries of flow regimes as well as the hydraulic characteristics of flow downstream of the grid drop-type dissipators.

Discussion of “Extraction of the Flow Rate Equation under Free and Submerged Flow Conditions in Pivot Weirs with Different Side Contractions” by N. Sheikh Rezazadeh Nikou, M. J. Monem, and K. Safavi

Discussion of “Extraction of the Flow Rate Equation under Free and Submerged Flow Conditions in Pivot Weirs with Different Side Contractions” by N. Sheikh Rezazadeh Nikou, M. J. Monem, and K. Safavi