Weir Models Research Articles

Flow characteristics and energy dissipation over stepped spillway with various step geometries: case study (steps with curve end sill)

Stepped weirs are used in a wide range of applications, designed to increase energy dissipation. In this study, laboratory experiments were conducted in a flume on six stepped weir models, with a downstream angle of θ = 26.6°. The physical models used were on a scale of 10:1, and tests of discharges up to 0.055 m3/s were carried out. Several step geometries including traditional step, sill and curve geometries were used to study flow behavior and overall energy dissipation. The laboratory investigations were augmented by modelling numerically the within step flow and energy behavior using a 2-D CFD model, incorporating the k-ε model for turbulence closure. The results showed that energy dissipation was greatest for the curved steps by about 10.5%, where it was observed that the skimming flow regime was shifted to a higher discharge range. Numerical modelling results showed good agreement with the experimental results. An inspection of the modelled streamlines highlighted the increase in vortex intensity for the curve model, reflecting the strong circulation observed. The predicted stepwise energy dissipation showed the energy dissipation increase when the step number Ns increases. For the range of step height hs, tested, our results showed that energy dissipation increased with step height. The results from this study can be used to inform engineering design for steps with θ = 26.6° and provide estimates of the expected energy dissipation and residual energy.

An Investigation on Hydraulic Aspects of Rectangular Labyrinth Pool and Weir Fishway Using FLOW-3D

Two different arrangements of the weir (i.e., straight weir and rectangular labyrinth weir) were used to evaluate the effects of geometric parameters such as weir shape, weir spacing, presence of an orifice at the weir, and bed slope on the flow regime and the relationship between discharge and depth, variation and distribution of depth-averaged velocity, turbulence characteristics, and energy dissipation at the fishway. Computational fluid dynamics simulations were performed using FLOW-3D® software to examine the effects on flow conditions. The numerical model was validated by comparing the calculated surface profiles and velocities with experimentally measured values from the literature. The results of the numerical model and experimental data showed that the root-mean-square error and mean absolute percentage error for the surface profiles and normalized velocity profiles of plunging flows were 0.014 m and 3.11%, respectively, confirming the ability of the numerical model to predict the flow characteristics of the pool and weir. A plunging flow can occur at values of L/B = 1.83 (L: distance of the weir, B: width of the channel) and streaming flow at L/B = 0.61 for each model. The rectangular labyrinth weir model has larger dimensionless discharge values (Q+) than the conventional model. For the conventional weir and the rectangular labyrinth weir at submerged flow, Q is proportional to 1.56 and 1.47h, respectively (h: the water depth above the weir). The average depth velocity in the pool of a conventional weir is higher than that of a rectangular labyrinth weir. However, for a given discharge, bed slope, and weir spacing, the turbulent kinetic energy (TKE) and turbulence intensity (TI) values are higher for a rectangular labyrinth weir compared to conventional weir. The conventional weir has lower energy dissipation than the rectangular labyrinth weir. Lower TKE and TI values were observed at the top of the labyrinth weir, at the corner of the wall downstream of the weir, and between the side walls of the weir and the channel wall. As the distance between the weirs and the bottom slope increased, the average depth velocity, the average value of turbulent kinetic energy and the turbulence intensity increased, and the volumetric energy dissipation in the pool decreased. The presence of an opening in the weir increased the average depth velocity and TI values and decreased the range of highest TKE within the pool, resulted in larger resting areas for fish (lower TKE), and decreased the energy dissipation rates in both models.

Investigation of labyrinth weirs discharge coefficient with the same length

One of the approaches to reduce flood depth in dams and rivers is the application labyrinth weirs instead of simple linear weirs. Labyrinth weirs have a longer length than linear weirs; therefore, the flood will pass through it with a lower depth. In this study, two types of triangular and semicircular labyrinth weirs were experimentally investigated. Experiments were performed in a flume with a width of 0.8 m and a flow discharge of up to 70 L/s. Eight weir models with a thickness of 4 mm were made, of which four models are triangular weirs and four models are semicircular weirs. Weirs were used in two types, one-cycle and two-cycle. The height of the weirs is 15 cm and the ratio of the weir length to the flume width (L/W) is equal to 1.57. The results showed that the increase in the total water head ratio (HT/P) decreases the discharge coefficient in all models, which is due to the increase in the Nappe interference and the local submergence. Also, increasing the number of cycles in labyrinth weirs has reduced its efficiency. The reason for this decrease is the impact of the issuing jets at the junction of the cycles and the flow disturbance over the weir. The comparison between triangular and circular weirs showed the better efficiency of triangular weirs. In addition, the results showed that the placement of the top of the cycle towards the upstream will cause a better performance in the weir. It seems that the low angle of the weir wall in the downstream with the channel wall causes the Nappe flow to collide with the channel wall and consequent local submergence will ultimately reduce the discharge coefficient.

Experimental Study of Flow Regimes of Stepped Weir


 Depending on the discharge and the stepped weir's dimensions, flow over a stepped weir can be primarily divided into three different flow regimes: nappe, transition, and skimming. The different properties for each flow regime make the decision of the flow regime an important component in the design of a stepped weir. Five stepped weir models have been used in experiments to determine the flow regime limits for these weirs. The models were made with various numbers of steps (3, 5, 7, 10, and 14) and downstream slope angle of 30˚. The configurations of steps that tested were flat step, fully pooled step, and zig zag pooled step . The results showed the end sills have a large impact on the type of flow regime. Based on the experimental data for flow regimes (nappe flow , transition flow and skimming flow ), a new set of empirical equations was proposed, with a determination coefficient〖 R〗^2 for these regimes (0.87, 0.71 ,0.7 ) respectively.
 
 

Analysis of Stability Safety Factors of Gabion Weir Models against the Wall and Water Level Variation

Analysis of Stability Safety Factors of Gabion Weir Models against the Wall and Water Level Variation

Experimental study of effect of creating an additional cycle along the lateral crest of the labyrinth weirs

One of the practical and economical ways to enhance the discharge capacity is to use labyrinth weirs. The longer crest length in labyrinth weirs than in linear weirs has caused these weirs to have both a higher discharge coefficient and water discharge capacity than a linear weir. In the present study, the discharge coefficient of trapezoidal and triangular labyrinth weirs was investigated by creating an additional cycle along the lateral crest of the weir. By constructing 10 physical models of labyrinth weirs, tests were performed in the hydraulic and sediment laboratory of the Khuzestan Water and Power Authority (KWPA). Dimensional analysis by the Buckingham method revealed the discharge coefficient (Cd) as a function of variable parameters such as the total hydraulic head to weir height ratio (Ht/P) and weir shape factor (Sf). The results of experimental tests showed that at the hydraulic head ratio (Ht/P) of 0.1, the TP weir had a higher discharge coefficient of 3.5% than the TPTPO weir and 2.5% than the TPTRO weir. However, at a hydraulic head ratio of 0.12, the TR weir had a lower discharge coefficient of 4.6% than the TRTPO weir and 6.9% compared to the TRTRO weir. For the hydraulic head ratio of 0.14, the TRTPI weir was 5.8% and the TRTRI weir was 9.4% higher than the TR weir. Statistical analysis using SPSS indicated that TRTPO and TPTRO weirs had the highest correlation with the cubic model.

Flow over embankment gabion weirs in free flow conditions

In this study, a series of laboratory tests were performed to investigate the effects of side ramp slope, crest length, and porous media properties on the flow regimes, water-surface profiles, discharge coefficients, and energy dissipation in embankment gabion weirs with upstream and downstream slopes. 24 physical models of solid and gabion weirs with three different upstream/downstream slopes (90°, 45° and 26.5°) were created. To investigate the complexity of flow over the porous-fluid interface and through the porous material, three-dimensional (3D) numerical simulations were developed. In numerical simulation, the standard k-ε turbulence model was utilized. A structured mesh domain was used to simulate the physical model. Water surface profiles above the porous weirs were used for comparison between the numerical simulations and measured data. These comparisons helped determine variables in the numerical simulations. Numerical simulation enables visualization of streamlines around and through the gabion weirs. In addition, mean stream wise velocity profiles above and within the porous structures were obtained. Numerical simulations showed that a reduction in the slope of the upstream face leads to an increased curvature of streamlines and the velocity distribution exhibits a non-uniform wavy shape due to the geometrical properties of the weirs. As the velocity profiles move downstream, the velocity distribution within the porous structures were more affected by the presence of the pores. The experimental results show that decreasing upstream slopes, from 90° to 26.5°, leads to decreased discharge coefficients. However, in all cases, gabion weirs lead to greater discharge coefficients than those of similar solid weirs. For milder side slopes, discharge ratios (flow passing through all faces of the gabion weirs over the inlet discharge) decreased nonlinearly. Moreover, with increasing the inlet discharge, relative energy dissipation was reduced up to 45% in gabion weirs.

3D Printing Technique for Experimental Modeling of Hydraulic Structures: Exemplary Scaled Weir Models

3D printing is a fast growing industry and is affecting many areas of our daily lives, e.g., in medical fields, mechanics, as well as engineering. For hydraulic experimental modeling, this technique offers a new alternative that could enable a more sufficient and rapid model fabrication, especially for models that feature complex geometries. The present study thus evaluates the feasibility of applying 3D printing to fabricate scaled hydraulic experimental models for laboratory use. Various weir models were printed and compared to conventionally produced reference models in terms of the fabrication process, resulting discharge coefficients, and hydraulic performance. Results show that while being more cost- and time-effective during the fabrication process, properly 3D printed models were able to fulfill experimental requirements and deliver accurate results with a relative deviation less than 5% compared to conventionally fabricated models. The printing layer height was found to be the most critical parameter influencing the model’s final quality. Associated with the additive building approach, surface irregularities of 3D printed models were noted to be able to cause undesired nappe behavior, which might affect experimental results under certain conditions. To avoid such issues, a reduction of plotted layer heights or additional surface improvements could be helpful. Based on experimental results and visual assessments, 0.4 mm layer height can be recommended as a good compromise for model configurations tested herein.

FLOW AND ENERGY DISSIPATION OVER A CYLINDRICAL STEPPED WEIR

The great economic importance of increasing the energy dissipation flow rate in stepped weirs prompted researchers to make several changes to the geometrical shape. In this study, (36) physical models were constructed to compare cylindrical stepped weirs with traditional weirs. (27) Models of cylindrical stepped weirs and (9) traditional stepped weirs were based on three heights and three diameters of steps. There are three shapes of the weir steps (Fc = all the steps in a circular shape, i.e., without cutting), (Fc & Hc = one round and the other half cut, respectively) and (Hc = all the steps are cut in half). The study showed that the percentage of energy dissipation in weirs increases with the height of the weir (P). Increasing the diameter of the degree (D) and increasing the number of steps (n), and changing the shape of the degrees, as the case (Fc & Hc) was better than the case (Fc). In contrast, the state (Hc) was the best among the other instances in the percentage of flow energy dissipation. The cylindrical gradient weirs are more efficient than traditional stepped weirs by approximately (%10), and the highest value for the energy dissipation of the flow was obtained for stepped cylindrical weirs (%67.27).

Analysis of Knock-Down Weir Model Shear Stability against Wall Rudeness based on Soil Type Variation

An increase in seawater that experiences high tides can cause tidal flooding. Tidal flooding in the Semarang area requires quick and precise handling, so an emergency dam is needed to deal with seawater overflow or tidal flooding. This study discusses the Knock-Down weir as a practical emergency weir. This study also aims to test the shear stability of the Knock-Down weir model against wall roughness based on variations in soil types, namely: masonry, gravel, sand, and clay. The Knock-Down weirs can be arranged vertically, horizontally, and as needed. The method used is descriptive qualitative. There are four forms of Knock-Down weir arrangement and the safest against wall roughness in various types of soil is prioritized. They are (1) L shape filled with sand + water, (2) Form I filled with sand + water, (3) Form I filled with water, and (4) Shape L filled with water. The results of the research on the safest Knock-Down weirs on shear stability are (1) L shape filled with sand + water, at a height of 1m weirs, shear stability against masonry (3,13), shear stability of gravel (2.09), shear stability to sand (1.67), shear stability against clay (1.25).

The hydraulic investigation of inflatable weirs

Abstract In this research, the models of Inflatable weirs with internal pressures of 0.5 and 1.4 at three heights of 0.15, 0.2 and 0.25 m were constructed. The deflectors were used in two geometric sections, including rectangular and triangular shapes, and they were installed at angles of 30, 45, and 60 degrees downstream of the weir body. The results showed that the value of the Cd changes between 0.28 and 0.35 while the range of the ratio of the upstream flow head on the crest to the radius of the downstream side of the inflatable weir varies between 0.2 and 1.5. The flow by crossing over the inflatable weir and colliding with the surface of the downstream stilling basin loses its energy by about 10–85%. The relative horizontal distance of the projectile-jet from the crest varies between 1.6 and 2.8. The effect of the deflector on the Cd is negligible due to being located in the supercritical part of the weir. Examination of the obtained results declared that the deflector has a considerable effect on energy dissipation.

Hydraulic Performance of Sharp-Crested Labyrinth Weir

Weirs are used as a control structure in the waterways. Among the influencing geometrical parameters on the weir performance is the total crest length. Experimental work on 27 geometric models of two-cycle Labyrinth shape crest weir is tested. The tested physical models consist of three weir heights, three apex widths and the sidewall angle is between (4.67°≤ α ≤ 19°), with three models of rectangular labyrinth weirs. The weirs of the wider apex and the same total length perform better and its coefficient of discharge is higher. Labyrinth weirs of longer sidewall length and contents same apex width performance batter. The larger value of sidewall angle and for a constant apex width reduces the value of discharge coefficient. The value of Cd range from (0.34-0.83) for the ratio of upstream head to the weir height (h/P) is ranged (0.08-0.48). The equations to predict the value of the discharge coefficient are suggested within the limitations of the present study.

Determination of Discharge Coefficient for both Semicircular and Triangular Labyrinth Weirs

A Labyrinth weir is a type of nonlinear weir folded in plan-view, with the ability to pass a large flow at low heads due to an increase in the effective length of the weir crest for a given channel width. The discharge coefficients (Cd) were experimentally determined for both semicircular and triangular labyrinth weirs of varying sidewall angles (α) under free-flow conditions using eight physical models. Dimensional analyses are conducted using the Buckingham π theorem to find the dependent and non-dependent variables. A nonlinear empirical equation was developed using (Statistical Package for the Social Sciences 22) software. The findings show that the discharge coefficient decreases with the increase of headwater to (Ht/P) for both types of labyrinth weir with different plan forms. It is found that the efficiency of the semicircular and triangular labyrinth is higher than linear weir for (Ht/P ≤ 0.45) and decreases with increasing the value of (Ht/P) due to interference of flow between the layers in downstream. The obtained results revealed that the discharge coefficient (Cd) values obtained empirically using multivariable power regression and 5th degree polynomial equations considerably agree with the experimental data, for both of the semicircular and triangular labyrinth weirs. Furthermore, the correlation coefficient R2was (0.9951) and (0.9637) using 5th degree polynomial equation, and their values were (0.9643) and (0.9274) using multivariable power regression equation for both semicircular and triangular labyrinth weir models, respectively. The results in the present study compared quite well with the predicted results of the proposed equations obtained by other investigators.

MODEL OF FALLING POINT AT NAPPE TRAJECTORY FOR CREST GATE TYPE OF RUBBER WEIR

Crest Gate Rubber Weir is a modification of a rubber weir with an installed curved metal plate or crest gate in front of the rubber weir. This crest gate serves as protection for the rubber weir and increases the water level contained by the rubber weir. Although this kind of weir is widely used, the behavior of falling water after passing through or nappe has not been studied adequately. Previous studies of nappe trajectories apply to static weirs with a flat upstream face. The nappe trajectory of this Crest Gate Rubber Weir should be examined differently because it is affected by the curvature of the crest gate and the various angles formed by the weir. This study aims to find the effect of the weir angle with the nappe trajectory by conducting a hydraulic model test of the 18o, 35o, and 53o weir models. The research found that the nappe trajectory of this Crest Gate Rubber Weir is influenced by the design head (Hd) and the weir upstream slope or the ratio of height and length (P/L) of the weir. This finding is applicable for determining which part of the downstream apron is impacted most from nappe and may require special reinforcement.

Numerical and experimental modelling of flow at Tyrolean weirs

In this study, a small-scaled Tyrolean weir model was constructed in the laboratory environment and a series of experiments were conducted on it, for two different rack inclinations (θ1 = 18° and θ2 = 25°) and three different bar spacings (e1 = 3 mm, e2 = 6 mm and e3 = 10 mm) for a range of upstream flow discharges. The flow rates passing through the racks and going downstream over the racks were measured. Empirical equations for the discharge coefficient and water capture capacity of the Tyrolean weirs were determined by applying dimensional analysis to the parameters involved in the phenomenon. The related dimensionless parameters were presented with graphs and empirical equations for discharge coefficients were derived, coefficient of determination R2 of equations for θ1 = 18° and θ2 = 25° are found 0.838 and 0.825 respectively. According to results obtained from experimental data, Cd increases as the Froude number ((Fr)e) between bars increases and water capture capacity [(qw)i/(qw)T] of the racks decreases with increasing ((Fr)e). Also, a numerical model of the Tyrolean weir was generated by using Flow-3D software and it was shown that the results of the numerical analysis were very consistent with the physical model results at large bar spacing such as e = 10 mm. As the bar spacing (e) reduces, the success of the numerical model giving consistent results with physical model is decreasing.

The energy dissipation of flow over the labyrinth weirs

In this study, the energy dissipation of flow over the triangular and trapezoidal labyrinth weirs with one and two key cycles was investigated. The magnification ratios (MR) of models were 1.57, 2.57, 3.57, and 4.57. Results declared that the labyrinth weirs can dissipate the energy of flow between 85% and 70% considering the range of the relative head (ho/P) between 0.10 and 1.0. The lowest efficiency of labyrinth weirs concerning energy dissipation occurs when the ho/P is about 0.25. For values less than 0.60 of ho/P, by increasing MR, the performance of models is decreased. For values less than 0.30 of ho/P, the performance of the trapezoidal plan crest is about 10 percent lower than the crest with a triangular plan. For values greater than 0.30 of ho/P, the performances of labyrinth weir models are identical and are about 75%.

EXPERIMENTAL STUDY OF ENERGY DISSIPATION IN A SINGLE STEP CONDITION OVER A BROAD CRESTED WEIR

This research study the experimental performance of broad-crested weir with single-step by introducing U/S and D/S round-nose and analysing the parameters that have effect on the shape of the step and their effects on the flow characteristics and energy dissipation (E%) downstream (D/S) of the weir. Furthermore, empirical relations for E% and flow rate due to the influencing factors were derived. The results showed that the weir model with = 1.000 gives a higher E% in comparison with other weir models. Flow regimes were observed i.e nappe flow for small discharges, transition flow for intermediate discharges and skimming flow for higher discharges. Two model equations were obtained, the first to dteremine the flow rate over the weir models and the second relation to estimate E% in terms of, and Froude number. The model () can be used in the design of prototype weirs in terms of energy dissipation

EXPERIMENTAL STUDY OF FLOW THROUGH TRAPEZOIDAL WEIR CONTROLLED UNDER A SEMI-CIRCULAR GATE

Different parameters of a weir model have a great effect on the discharge coefficient. In this experimental study the effect of varying angle of a trapezoidal weir coupled with a below semi-circular gate is determined. The result showed that the higher the value of the higher the coefficient of discharge. The respective average discharge coefficient of the block model and the trapezoidal weir models are; 0.48031,0.48880, 0.49565, 0.49647, 0.49892 and 0.49934. As such the trapezoidal weir with has the highest value of average discharge coefficient =0.49934. Hence the most efficient. Linear and nonlinear regression analysis were used to generate mathematical equations that can be used to predict the flow rate Q for the combined weir-gate structure and the discharge coefficient of the most efficient model with respectively. The discharge coefficient for the most efficient weir model was found to be 3.81% more than that of the block model (with rectangular weir). The predicted coefficient of discharge for the most efficient model was also found to be in good agreement with the observed discharge coefficient with a percentage error in the range of 0.4%

Impact of the Weir Slit Location, the Flow Intensity and the Bed Sand on the Scouring Area and Depth at the Dam Upstream

A total of 48 experiments were conducted to investigate the impact of slit weir dimensions and locations on the maximum scour depth and scour area created upstream. The slit weir model was a 110 mm slit opening, and it was installed at the end of the working section in a laboratory flume. The flume was 10.0 m long, 30 cm wide, 30 cm deep, and almost middle. It includes a 2 m working section with a mobile bed with 110 mm in thickness. In the mobile bed, two types of nonuniform sand (with a geometric standard deviation of 1.58 and 1.6) were tested separately. The weir dimensions and location were changed with flow rates. Then dimensions of the slit weir were changed from 60 x 110 mm to 60 x 70 mm (width x height), while the location of the slit weir was changed from the center of the flume to its side. Finally, the flow rates were changed from 2.6 to 8 l/s. The maximum value of scour depth and scour area was recorded 72 mm and 32357 mm2 when the slit height, the flow rate, D50 of the movable bed were 110 mm, 8 l/s, 0.3 mm, respectively.

Sediment Movement over Type A Piano Key Weirs

This investigation deals with the mechanics of movement of singular quartz gravel and coarse sand riverbed particles upstream and over the inlet key of three Type A piano key weir (PKW) models, which were recorded with a high-speed camera. Acoustic Doppler velocimeter was used to obtain the upstream bed shear stress. The sediment threshold and regime over the upstream bed were compared with the previous investigations and found to be within the ranges. Generally, a sediment particle decelerates as it approaches the inlet key, but accelerates over it due to flow contraction and an increase in shear stress. Rolling and saltation regimes were observed over the key. The maximum particle velocity at the key end was highest in the 1-cycle model, then the 2-cycle model, then the 3-cycle model. Computational fluid dynamics (CFD) simulation shows a rapid increase in shear stress at the key end. For the used models, PKW required 17%–43% of additional shear stress on the upstream bed to pass sediment over the key. This study is useful for the in-channel application of PKW and sediment flushing over it.