HYDRAULIC ANALYSIS OF COMPOSITE HYDRAULIC STRUCTURE CONSIDERING EXISTING OF PIRE

The purpose of the present study is to examine the influence of baffles presence at downstream system on weir gate hydraulic response. Two baffles configuration (triangle and angle shapes) are installed in bed flume. Two different spacing are used between the baffles and two different directions for baffles are also adopted. The study tries to investigate the variation in upstream Froude number, downstream Froude number, Reynolds number, actual discharge, discharge coefficient, downstream average water depth and the hydraulic system efficiency which is expressed as function of downstream water depth. It has been shown that the number of baffles has a direct and significant impact on flow hydraulic characteristics of weir-gate structure regardless of the spacing between baffles and the direction of baffles related to flow. Baffles number and spacing have essential impact on the water flow velocity of system and this impact leads to increase the flow resistance. The results clarify that the upstream Froude number, downstream Froude number, Reynolds number, actual discharge and discharge coefficient are decreased with the increase in baffles number except the average downstream water depth which increases with increase in baffles number. The efficiency of hydraulic system gives a good indicator for using baffles with weir-gate structure. At the end this paper shows a fruitful result of efficiency. This experiment run condense on the baffle’s numbers and directions with respect to the water flow direction at the downstream regime. So, the rises in the water level relies on the numbers and directions of the baffles as compare to the case without using baffles at the flume downstream region. The actual discharge and weir-gate discharge coefficient are more sensitive to the increase in the baffles’ numbers and the baffles direction with respect to the water flow direction

سرریز جانبی به عنوان یک سازه کنترل و اندازه‌گیری جریان به صورت گسترده‌ در زمینه‌هایی نظیر مهندسی هیدرولیک، آبیاری و محیط زیست مورد استفاده قرار می‌گیرد. جریان روی سرریز جانبی به عنوان یکی از مسائل جریان متغیر مکانی با کاهش بده شناخته شده و با استفاده از روش‌های آزمایشگاهی، مدل‌سازی عددی و تحلیل نظری بررسی می گردد. تحقیق حاضر به بررسی خصوصیات جریان روی سرریز جانبی ذوزنقه‌ای واقع در یک کانال اصلی با مقطع مستطیلی و در شرایط رژیم جریان زیربحرانی می‌پردازد. پروفیل جریان بر روی سرریز جانبی و ضریب بده جریان با استفاده از نتایج آزمایشگاهی مورد بررسی و تحلیل قرار گرفته است. با توجه به نتایج این تحقیق و توصیه محققین پیشین، بهترین مقطع برای اندازه‌گیری پروفیل جریان در امتداد محور مرکزی کانال معرفی شده است. مشخص گردید که ضریب بده سرریز جانبی ذوزنقه‌ای به عدد فرود جریان بالادست، نسبت ارتفاع سرریز به عمق جریان، نسبت ارتفاع روگذری به عمق جریان و شیب جداره سرریز بستگی دارد. در این تحقیق برای ارزیابی ضریب بده و ارائه معادله بده برای سرریز جانبی، از تئوری سرریز معمولی استفاده شده است. برای این منظور از سه عمق مشخصه به عنوان هد سرریز استفاده شد و بر اساس هر یک از این اعماق رابطه‌ای برای ضریب بده ارائه گردید. مقایسه نتایج با داده‌های آزمایشگاهی نشان داد که عمق متوسط جریان بهترین جواب را برای ارزیابی ضریب بده ارائه می کند. متوسط خطای برآورد ضریب بده با استفاده از عمق متوسط جریان برابر با 6/2 درصد می‌باشد. لذا می‌توان این روش را برای مقاصد عملی پیشنهاد نمود.

Discordance and concordance play a significant role in the hydraulic response for the flume, open channel, hydraulic structure, and flow field measurement. Bed discordance and bed concordance are regarded as common problems in open channels. Discordance is the dominant one, which could have an effect on the hydraulic structure that is constructed inside the channel. This paper deals with the impact of bed flume discordance on hydraulic flow characteristics at the weir-gate downstream hydraulic regime. Four configurations with different lengths and heights of the bed flume discordance are adopted here to investigate the impact of these configurations on the hydraulic characteristics. In addition, one configuration of the bed flume concordance is adopted to compare with the other four configurations. At downstream, the average water depth becomes dimensionless by dividing by upstream water depth, vertical distance between weir and gate, length of downstream, length of concordance, and length of discordance in order to evaluate the inequality in the distribution of Froude number. On one hand, certain results appear strongly between Reynolds number and Froude number at downstream, actual discharge and flow velocity at downstream, flow area past the gate and Froude number at downstream. On the other hand, there was a complex dramatic relation between the weir-gate discharge coefficient and Froude number at downstream. Overall, the study shows that there is a good relationship between specific energy, water depth, and flow speed. Doi: 10.28991/HIJ-2022-03-03-09 Full Text: PDF

The experimental simulation between the composite hydraulic structure and the found obstacles in the downstream region is a challenging process due to the energy losses and kinematic dissipation. The current work focuses on a comparative analysis of free flow conditions that exist without obstacles and submerged flow conditions that occur due to obstacles. It indicates the evaluation of hydraulic variables and geometrical variables of composite hydraulic structure for both flow conditions. In addition, it includes an investigation of the interaction among these variables. The hydraulic variables include actual discharge, flow velocity, flow cross-sectional area that crosses the gate, downstream water depth, discharge coefficient, Reynolds number and, Froude number, while the vertical distance between the weir and gate represents the geometry variable. The interference between the weir discharge and gate discharge plays a significant role in the result fluctuation and variation for both flow conditions, while the form and size of the obstacles only have a major effect on the submerged flow. For both flow conditions, the water depth is investigated; there would be a drastic increase in water depth by using obstacles in the downstream area as compared with not using the obstacles. This study adopts different obstacles in shape and size, therefore, the variation of maximum and minimum water levels related to the location will occur.

A fuzzy logic model was constructed to predict hydraulic jump aeration efficiency. Fuzzy subsets and rules were created based on experimental observations and measurements carried out in a 0·5 m wide flume with upstream Froude and Reynolds numbers of 2·3–6·4 and 1·4–5·4 × 104, respectively. A strong correlation was found between the aeration efficiency and Froude number. Upstream Froude and Reynolds numbers were selected as input parameters for the model. In this study, rather than mathematical equations, linguistic expressions were used to relate the upstream Froude and Reynolds numbers with aeration efficiency in an IF–THEN format. The proposed fuzzy model made good predictions and captured the system dynamic behaviour. Experimental observations confirmed the fact that hydraulic jump can be used as an aerator and mixing device in water treatment plants. Estimation of the aeration efficiency of a hydraulic jump could be made by any designer with the help of the fuzzy logic procedure described in this paper.

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.

Side weirs are flow-diversion and flood control devices widely used in urban drainage, land drainage, and irrigation systems. The De Marchi equation is widely used for computation of side-weir flow. However, in this equation the variation of flow depth with longitudinal distance is expressed in implicit form. Many investigators focused on the relation between the coefficient of discharge and the upstream Froude number and other flow and/or geometric parameters. Presented herein is a general design method for side weir. Also presented is a concept that for subcritical flows over a side weir the flow characteristics are governed by downstream flow conditions and the geometric parameters of the channel and the side weir. The study is based on De Marchi's equation. The analysis is conducted through non-dimensionization of the parameters in the equation. The study results indicate that the side weir flow is a function of the downstream flow depth and Froude number, and the ratios of weir height to downstream depth and channel width to the product of weir length and discharge coefficient. Charts were produced and procedures were given for engineering design.

In this paper, an experimental study was carried out to investigate the characteristics of flow through inclined finite bump in a sloping rectangular open channel of constant width. Experiments were conducted with bed slopes of 0.00, 0.005, 0,010, 0.015, 0.020 and 0.025, and lump angles of 15°, 30°, 45°, 60°, 75 and 90', and relative heights, of 0.1, 0.2, 0.30, 0.40, 0.05 and 0.60 to study the variation of the energy loss and relative water depth with the main parameters affecting the finite hump in sloping channel. These parameters include the channel bottom slope, the upstream Froude number, downstream Froude number, hump angle and relative height. Non-dimensional design curves are provided to relate the flow characteristics. The results show that the rate of variation of the energy loss increases till a finite hump angle of about 30°. This rate of increase decreases behind this value of angle of finite hump. The energy loss increases with the increase of bed slope and relative height ratio. The energy loss is quite high at a relative height of 0.3. The effect of all parameters on the energy loss through the inclined finite hump analyzed and discussed.

The rectangular weir (notch) is a common device used to regulate and measure discharge in irrigation projects. The current research was based mainly on laboratory experiments studying the hydraulic characteristics of rectangular notches. Four rectangular notches were used in this research in different models. Notches for all models were designed with the same shape, arrangement, and width (4 cm), but differed in height, with examples at 6, 8, 10, and 12 cm. The main objective of this research was to study the influence of rectangular notch dimensions and upstream water depth on discharge coefficients.The results obtained from this research indicate that the relationship between the discharge coefficient and the upstream water depth is a power function. The values of the discharge coefficient increase with increases in the values of the upstream water depth. The relationship between the discharge coefficient and the Reynolds number is also a power function, and an increase in the Reynolds number leads to a decreased discharge coefficient. In addition, when the value of the Reynolds number is high (turbulent flow), the values of the discharge coefficient converge to an approximately constant value. The flow in all runs was subcritical and the relationship between discharge coefficient and Froude number was also found to be a power function. An increase in Froude number thus leads to a decrease in discharge coefficient. The slope of the discharge coefficient-Froude number curve values gradually decreases until the value the discharge coefficient reaches an approximately constant value. A dimensional analysis technique was used to estimate the values of the discharge coefficient for various rectangular notch dimensions, and an empirical equation for discharge coefficient estimating was derived using regression procedure. This equation has a coefficient of determination R2 of 0.955.

Based on experimental observations, for a subcritical, right-angled, equal-width, open-channel dividing flow over a horizontal bed, the contraction coefficient at the maximum width-contracted section in the recirculation region is almost inversely related to the main channel upstream-to-downstream discharge ratio. The energy heads upstream and downstream of the division in the main channel are found to be almost equal. Under the assumption that the velocities are nearly uniformly distributed at the considered boundaries, the depth-discharge relationship follows the commonly used energy equation. The predicted results correlate fairly with the experimental data from this and other studies. The energy-loss coefficient of a division is expressed in terms of discharge ratio, upstream Froude number, and depth ratio. An expression for practical engineering applications is to determine the maximum possible branch-channel discharge at a given upstream discharge with a prescribed downstream Froude number or the maximum possible downstream Froude number if both branch- and main-channel discharges are prescribed.

With the continuous operation of check dams, the silting elevation of the whole dam gradually increases. When the silting height is close to the elevation of the broad-crested weir, it will result in a large change in the hydraulic characteristics of the original flow pattern. For subsequent reinforcement work, it is necessary to know how excessive sediment deposition affects the overflow from the broad-crested weir into the spillway. However, few studies about discharge coefficients are available in the case of spillways with sediment. In this paper, the hydraulic characteristics and discharge coefficient of a broad-crested weir whose width is 270 mm are investigated with physical experiments under different siltation heights and discharges. The research shows that: (1) With the increase in siltation height, the water level on the weir decreases and the drop of the flow becomes smaller. The overall flow pattern tends to the open-channel flow pattern. (2) In the same siltation height condition, the water surface profile along the broad-crested weir rises with the increase in discharge, and the surface velocity of the water in front of the weir increases with the increase in discharge. However, in the same discharge condition, the water surface profile along the broad-crested weir decreases with the increase in siltation height, and the surface velocity of the water in front of the weir gradually increases, which reflects that the increase in siltation height improves the overflow capacity of the broad-crested weir. (3) The present empirical formulas for the discharge coefficient have large errors when there is sediment accumulation. Therefore, a new formula for the discharge coefficient with sediment deposition is obtained using experimental data and its maximum relative error is 4.02%, which can provide a theoretical basis for risk elimination and reinforcement work on check dams in the Loess Plateau.

The 3D flow over side weirs is investigated using Computational Fluid Dynamic (CFD). The study aims to assess the capability of ANSYS CFX code for modeling flow characteristics in a circular channel with side weir for subcritical flow condition. Twelve models were studied for some ranges of variables such as discharge, length and height of side weir. The numerical simulation was based on the solution of continuity and momentum equations for three dimensional, incompressible, steady and turbulent flow. The volume of fluid (VOF) method was used to predict the free surface changes and the RNG k-e model was employed for simulating the flow field. The experimental data of Uyumaz and Muslu (1985) were used for verification. For all models, the specific energy is obtained and the average energy difference at the upstream and downstream side of the weir was very small and the assumption of constant energy in the circular channel was acceptable. The numerical results predicted the changes in the water surface profile at the main channel central axis and indicated that the water level rises from upstream to downstream end of the weir. The discharge coefficient (Cd) variation with the upstream Froude number (Fr1) for different weir height and length were studied and it was found that the value of (Cd) decreased with the increase of (Fr1) value. For each side weir length, the variation of (Cd) with the ratio of the weir height to channel diameter (P/D) were studied and it was observed that with the increase of (P/D) ratio the value of the (Cd) increased. The relation between the (Cd) and the ratio of the side weir length to channel diameter (L/D) for different weir height were also investigated. It was noticed that the (Cd) value increased gradually as the (L/D) ratio increased. The combined effects of (Fr1), (P/D) and (L/D) on the (Cd) were studied for all models and an empirical expressions for describing this relation was obtained and it was found that (Cd) was a function of all the above parameter.

The weir-gate structure has special attention due to its ability to manage water quantity when placed in any waterway. The performance of this hydraulic structure relies on several hydraulic parameters and geometrical parameters in addition to the flow patterns in the waterway regime. In this paper, the structure assessment is based on the study of the effect of the weir flow area and some hydraulic parameters on the hydraulic and geometrical features of the weir gate. Regular and nonregular shapes have been used for the weir, and a nonregular shape has been used for the gate. Several experiments have been done in flume with a horizontal fixed bed. The hydraulic parameters include flow rate, discharge coefficient, gate flow area, downstream water depth, in addition to Reynolds number and Froude number, while the geometrical parameters include the vertical distance between weir and gate. Furthermore, a statistical analysis has been applied to show the variation in some hydraulic parameters. The statistical analysis comprises maximum, minimum, and average values for hydraulic parameters, respectively. The findings suggest that the discharge structure featuring a parabolic weir is more effective than alternative structures reliant on maximum, minimum, and average flow rates. To facilitate a hydraulic analysis, a correlation matrix and significance testing were utilized to illustrate the relationships among hydraulic and geometric variables. The correlation matrix indicates a strong relationship among hydraulic parameters, with values ranging from 0.73 to 1. Notably, the correlation coefficient between flow rate and Reynolds number is 1, reinforcing the hydraulic connection between these two parameters.

This study integrates a large eddy simulation (LES) model and volume of fluid (VOF) method to simulate the free-surface flows over inflexible circular-crested dams of different shapes. The simulated water depths and pressures on the dam surface are validated by the results of laboratory experiments. Then the numerical model examines the effects of the water depths and the Reynolds number on the hydrodynamic force and the discharge coefficient. The simulation results reveal that the time-averaged drag coefficient decreases as the downstream water depth H2 increases, while the influence of water depth H2 on the lift coefficients is less significant. Furthermore, the discharge coefficients of circular and elliptical dams, computed from the simulated velocity profiles over the crest of the dam, agree with the formulae suggested by previous studies when the downstream depth H2/H1 < 0.90. In contrast, the discharge coefficient of a tear-shape dam is slightly larger than those of circular dams.

Surface drainage systems play a key role in the urban system. To assess the flow intercepted by inlets, some approaches use recent experimental campaigns or are based on orifice or weir formulas. In this work, real scale experimental campaigns are used to define discharge coefficients to provide information for practitioners and inlet manufacturers. Tested discharge values range between 25–200 l/s whereas transversal and longitudinal slopes range from 0–4% and 0–10% respectively. Three grated inlets have been analyzed obtaining values of discharge coefficients in situations for which the flow completely covers the grates. Discharge coefficient ranges for supercritical flow conditions have been obtained and the strong relationship with the upstream Froude number has been highlighted. Considering the orifice approach, the discharge values range between 0.055–0.294, 0.033–0.431 and 0.054–0.423 for the Barcelona1, Meridiana and E-25 grated inlets respectively. Conversely, for weir assumption, the coefficients range between 0.009–0.244, 0.003–0.245 and 0.006–0.286.