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This study examines how the variability of the Manning coefficient (n) affects the position of hydraulic jumps downstream of hydraulic structures. Using a robust finite volume method and random field theory, the study investigates the impact of spatial variations in n on hydraulic jump characteristics. Two scenarios are considered: one with a stilling basin and one without. Both one-dimensional and two-dimensional spatial distributions of n are analyzed. The results show that without a stilling basin, there are significant variations in the location of hydraulic jumps in the riverbed. The uncertainty in the location of the hydraulic jump is much higher than the uncertainty in the values of conjugate depths. Additionally, one-dimensional spatial distribution of n leads to higher standard deviations in the estimated location compared to two-dimensional distribution. In scenarios with a stilling basin, increasing riprap length causes the hydraulic jump to move upstream, while standard deviation remains constant. [ABSTRACT FROM AUTHOR]

The experimental evaluation of the performance of a corrugated apron under free flow subcritical and submerged conditions was conducted, with a focus on scour patterns over the apron. Comparative analysis with a smooth rigid apron revealed an increase in scour depth upon the application of the corrugated apron under free and submerged jet flow conditions. The implementation of a corrugated apron resulted in a considerable reduction in scour depth and length compared to a smooth rigid apron. The maximum reduction in scour depth and length amounted to 79% and 83%, respectively, while the minimum reduction observed was 13% in scour depth and 11% in scour length. Additionally, investigations into velocity and turbulence characteristics over both smooth and corrugated aprons were conducted. It was observed that the rate of turbulence intensity increase within the scour hole due to the presence of a smooth apron surpassed that of the corrugated apron. Scour downstream of the corrugated apron exhibited distinct delineations, including regions of jet diffusion, transition, acceleration, and a recirculating zone near the bed of the scour hole. [ABSTRACT FROM AUTHOR]

The phenomenon of hydraulic jumps has been widely studied in laboratory flumes. However, few studies have been made to bridge the discrepancy encountered in the formulation of relations ascribing hydraulic jumps based on laboratory model studies and that occur in natural conditions. Most of the predictive formulae for sequent depth ratio and length of jump proposed in the literature have not been verified in the field. The present study attempts to link the field investigation data of hydraulic jump in a weir with laboratory channel flume observation for similar flow conditions. The hydraulic jump parameters were collected in the field using feasible technologies in the study weir. The weir selected for this study has geometric, kinematic and Froude similarities with the laboratory model. The comparison of laboratory model data and field measurements showed inconsistency. It is observed that the sequent depth ratio and length of the jump are inaccurately predicted by the laboratory relation compared to the field observations by the laboratory relation. A fieldvalidated-based relationship is suggested for the calculation of sequent depth and length of jump in a smooth rectangular channel for Froude numbers ranging from 4 to 10. [ABSTRACT FROM AUTHOR]

Building flood reduction dams for territory protection is very often necessary as it allows the reduction of peak flows during flood events by creating a storage in upstream areas. An online structure with such characteristics is outlined, presenting one or more openings in order to allow normal and moderate flows to pass downstream. A stilling basin is provided downstream of the openings and, on one side of the flooded area, a spillway weir is set. For low river flows, the openings will act as free-surface weirs. The openings are equipped with a sill in such a way to let the discharge independent of the downstream flow conditions. For moderate flood flows, the water level upstream of the dam will rise, and the openings will become submerged, effectively behaving as an orifice arrangement. For large flood flows, the crest of the flood spillway weir is reached and they will be discharged via both the orifice structure and the flood spillway structure. The silled openings and the stilling basin are one only hydraulic complex. Since no examples exist of their behavior as a whole, the aim of this paper is to give the designers the opportunity to size them given the basic requirement of the flood reduction dam, i.e. the max discharge allowed downstream. For this reason, the paper will focus on the opening discharge coefficients, the stilling basin energy dissipation and water level. Both the orifices and the stilling basins were studied starting from the hydraulic models of three dams that were built in Calabria (Italy). The structures of the stilling basins are original. The results appear in dimensionless form and offer useful guidance for similar hydraulic cases, with the exception of specific terrain related issues. Finally, an example of a preliminary design of orifices and stilling basin is presented. [ABSTRACT FROM AUTHOR]

The flow of a thin film over a rotating disk is crucial in many industrial applications, such as spin coating and jet cooling. Accurate prediction of hydrodynamic features is essential for optimizing these processes. In this study, we examine the vertical downward impingement of a circular Newtonian liquid jet on a horizontally rotating disk, focusing on two distinct regimes based on the rotation level. For a stationary disk and low rotation speed, a continuous hydraulic jump is formed, while increased rotation speed leads to the transformation of the jump into a hump. A composite mean-field thin-film approach is utilized to analyze the flow dynamics in different regions of the domain. The effects of gravity and rotation are considered by developing a model to capture the continuous jump and vortex structure. The influence of rotation on the laminar boundary layer near impingement is found to be negligible. Specific conditions for gravity and rotation are established to differentiate between the jump and hump regimes. The model is validated for both regimes against existing experiment. In the jump regime, the flow transitions from predominantly azimuthal near the disk to predominantly radial toward the free surface, while in the hump regime, the flow maintains an azimuthal character around the hump. The vortex associated with the jump diminishes with increasing rotation speed, indicating the occurrence of a type-0 jump on a rotating disk. For small gravity, the vortex does not form in conjunction with the jump at any rotation level. In the case of small rotation, large gravity, and large disk size, the film exhibits a hydraulic jump near impingement followed by a sharp rise in thickness near the edge of the disk. [ABSTRACT FROM AUTHOR]

Foehn winds have been a focus of research in mid‐latitude mountainous regions for more than 150 years, where their onset is typically associated with warm, dry, and gusty winds. This research has now extended into high latitude regions, yet research of foehn winds in subtropical and tropical regions remains scarce. Here we present results from the first investigation of foehn winds in the subtropics of Southeast Queensland (SEQ), Australia. Analysis of meteorological records found that foehn winds occur throughout the year with peak frequency and duration in late winter (August) associated with the passage of shortwave troughs over southern Australia. Modeling of wind fields and atmospheric boundary layer conditions for three case studies was conducted using the Weather Research and Forecasting (WRF) model. Results showed foehn events in SEQ can be associated with mountain waves and hydraulic jump features in the lee of topographic barriers. Over lee slopes, acceleration of wind speeds and topographic channeling of foehn winds was found to occur, along with substantial increases in air temperature, and decreases in relative humidity. Warming of the foehn airstream is believed to occur primarily through isentropic drawdown with a likely contribution from surface sensible heat flux. Recommendations for future research are made in light of the importance of foehn winds to wildfire management and mitigation in SEQ. Plain Language Summary: Foehn winds form as airflow associated with the passage of large‐scale weather systems descends over the lee slopes of mountains and escarpments. These warm, dry, and gusty winds significantly change the meteorology in the lee of mountains and escarpments causing increases in air temperature, wind speed and decreases in humidity. While foehn winds have been a focus of mountain meteorology in mid‐latitude regions for more than 150 years, research of foehn in other climate zones is scarce. Here we present results from the first investigation of foehn winds in the subtropics of Southeast Queensland (SEQ), Australia—a region where foehn winds significantly increase the threat of wildfires. Results show that foehn winds in this region are most common in late winter (August) with the passage of shortwave troughs over southern Australia. Using the Weather Research and Forecasting (WRF) model we find that foehn wind events in SEQ may be associated with mountain waves and other dynamical features in the lee of topography. We suggest avenues for future foehn wind research in SEQ given their importance to wildfire management and mitigation. Key Points: Subtropical foehn winds are accurately modeled using the Weather Research of Forecasting modelFoehn warming of +10 to +14°C was simulated and caused by isentropic drawdownModeling showed mountain wave and hydraulic jump features in trans‐barrier flow [ABSTRACT FROM AUTHOR]

This study aims to develop and assess seven machine learning (ML) models, including an Artificial Neural Network (ANN), Gradient Boosting (GB), Extra Trees (ET), Lasso Regression (LASSO), Least Angle Regression (Lars), Random Forest (RF), and Adaptive Boosting (Adaboost), that are effective and simple in forecasting the roller length of a hydraulic jump in a rectangular horizontal canal. This study also proposes a novel approach for applying the Buckingham Pi theorem to ascertain four model inputs and one output, corresponding to five dimensionless Pi terms that have not previously been explored. The impact of channel surface roughness, fluid viscosity, channel geometry, and gravity on the hydraulic jump's roller length was considered to improve the model's performance. Furthermore, the importance of input features was determined, resulting in two model input scenarios. The scenario with four inputs containing the inflow Reynolds number Re1* surpasses the three-input scenario. Because of their high accuracy and efficiency, six ML models outperformed three empirical equations. The GB, ANN, and ET models showed the best performance in both validation and testing phases, whereas LASSO, Lars, RF, and Adaboost performed with lower precision, in descending order. Regarding the ANN model, the best has two hidden layers of sixteen neurons each. In the validation and testing phases, this model achieves the highest Nash–Sutcliffe efficiency of 0.992 and 0.933, respectively. As a result, this study recommends using the GB, ANN, and ET models to forecast the roller length of the hydraulic jump instead of empirical equations when the inflow Froude number, Fr1, varies between 2.4 and 15.9. [ABSTRACT FROM AUTHOR]

This study conducted experiments to investigate the impact of bottom obstacles, specifically broad-crest weir-type and cylindrical obstacles, on the flow within a sewer pipe. It was observed that these two types of obstacles, when possessing the same cross-sectional area and length, exhibited nearly equivalent hydraulic responses for both supercritical and subcritical flows. The obstacle height was found to be the primary factor responsible for choking and the transition between different flow regimes. The results of the one-dimensional analysis show that the threshold value of obstacle height depends on the approaching flow conditions, including the Froude number and the filling ratio that is defined as the flow depth to the pipe diameter. In the context of a partially blocked sewer, the relationships established by using the one-dimensional model between the size of the bottom obstacle and the inflow characteristics enable the identification of flow regimes, assessment of reduced hydraulic capacity, and evaluation of local energy loss. The findings of this study elucidate the hydraulic behavior of obstructed sewers, contributing to the development of more effective strategies for the identification of obstructions through monitoring data. [ABSTRACT FROM AUTHOR]

Flip bucket is a type of energy dissipator structure. Flip buckets can sometimes be improved by adding wedge-shaped deflectors. This research introduced the best height proportion of used deflector on the flip buckets to increase energy dissipation. It used 4 types of deflector series including 32, 45, 47 and 55 degrees toward horizon with two different regular and irregular layouts and 19 different heights from 2.31 to 5.6 cm and in different hydraulic condition and the results were compared with a flip bucket without a deflector. The characteristics of laboratory flume were: length= 7.5 m, width= 0.58 m and height= 1.6 m. The results illustrates that the energy dissipation in the model with deflectors increased from 11.83 to 19.38 percent as compared with model without a deflector. The greatest percentage of energy dissipation was 80.74% which observed at a deflector angle of 55° and a discharge of 10 L/s, at deflector’s ratio of n=0.8 and in non-uniform layout and in free hydraulic jump. Larger deflector angles and side lengths initially boosted energy dissipation, but this effect plateaued or even reversed at very large angles. For calculating energy dissipation and hydraulic jump length parameters, the regression relations were extracted in this research and results of this relations were compared with results of the gene expression programming (GEP), random forest (RF) and multivariate adaptive regression splines (MARS) methods. The results showed that the RF method is the most accurate method for calculating energy dissipation and hydraulic jump length parameters. [ABSTRACT FROM AUTHOR]

In this study, the main properties of the hydraulic jump in an asymmetric trapezoidal flume are analyzed experimentally, including the so-called sequent depths, characteristic lengths, and efficiency. In particular, an asymmetric trapezoidal flume with a length of 7 m and a width of 0.304 m is considered, with the bottom of the flume transversely inclined at an angle of m = 0.296 and vertical lateral sides. The corresponding inflow Froude number is allowed to range in the interval (1.40 < F1 < 6.11). The properties of this jump are compared to those of hydraulic jumps in channels with other types of cross-sections. A relationship for calculating hydraulic jump efficiency is proposed for the considered flume. For F1 > 5, the hydraulic jump is found to be more effective than that occurring in triangular and symmetric trapezoidal channels. Also, when [ Lr/(h2-h1)s] mes > 8 and Lr/h2 > 5, the hydraulic jump in the asymmetrical trapezoidal channel downstream of a parallelogram sluice gate is completely formed as opposed to the situation where a triangular sluice is considered. [ABSTRACT FROM AUTHOR]

ABSTRACTGabion steps on stepped spillways can be a suitable alternative to solid impermeable steps due to their economic advantages, ease of implementation, stability through water pressure reduction, and energy dissipation. This study explores hydraulic jumps and the rate of energy dissipation downstream of gabion stepped spillways under different flow regimes. Six stepped spillway models, including a solid spillway with solid steps and five models with gabion steps, were made with different step arrangements in a 26.6° slope (1 V:2 H) facility. The results showed that in stepped spillways with gabion steps and in the nappe flow regime, as a result of seepage flow through the pores of the aggregate and overflow passing the gabion step, there is an increased energy dissipation associated with a smaller sequent depth ratio, the relative length of jumps, and roller length compared to solid and impermeable steps. The reduction in the hydraulic jump depends on the flow regime and the arrangement of the gabion steps. For skimming flows, smaller energy dissipation rates were measured downstream of the gabion step. On average, when gabion steps are placed on all steps, the sequent depth ratio, jump length, and roller length decrease by 3.34%, 8.61%, and 8.14%, respectively, compared to solid steps. The maximum energy dissipation was measured at the downstream end of the gabion steps with a value of 74.4%, which is 5.03% more than that with the solid steps. On the solid stepped spillway, the nondimensional residual head was 4.65, and for the same flow conditions, the average dimensionless residual head on the gabion steps was 4.21.

Intake structures are commonly used in drainage systems to redirect surface rainfall runoff into underground tunnels. The Hong Kong West Drainage Tunnel (HKWDT) system is designed to capture stormwater from steep upland catchments during periods of heavy rainfall, concurrently maintaining a minimal environmental flow downstream during dry weather. However, during heavy rainfall events, excess rainfall water is often directed into the drainage system, presenting a significant challenge to the urban drainage system. Undistorted Froude scale physical models and computational fluid dynamics (CFD) models are developed to investigate the flow performance. In this study, effects of various design parameters on water diversion performance are examined across a wide range of inflow conditions. Steeper channel bottom slopes leading to a larger proportion of water being directed downstream. Extending the length of the bottom rack effectively reduces adhering flow. Introducing a transverse barrier generates a hydraulic jump, which increases flow diversion into the LFC. With higher barrier heights, the hydraulic jump becomes stronger, facilitating greater water diversion into the downstream sewage system. The results indicate potential solutions to these challenges and provide valuable insights into optimizing flow diversion performance in intake structures, particularly in areas characterized by steep terrains and varying flow conditions. [ABSTRACT FROM AUTHOR]

Hydraulic jump is used to dissipate excessive flow energy in stilling basins to control erosion on the downstream side. The literature review revealed that the convergence of the side walls in a USBR type II stilling basin has enhanced energy dissipation by stabilizing the hydraulic jump. Taking this into account, a Computational Fluid Dynamics (CFD) model was created using CFD code to analyze the hydraulic efficiency of a USBR type III stilling basin with varying degrees of side wall convergence. Additionally, alterations were made to the standard Impact Blocks geometry to evaluate their effect on energy dissipation. The side walls of stilling basin were converged from 0.5° to 2.5° (with an increment of 0.5°). Study results indicated an increase in hydraulic jump efficiency from 1.6 to 14.5% due to increase in wall convergence. Modified Friction Blocks also enhanced the energy dissipation up to 2%. Post-jump Froude number values were found in acceptable range of 0.6 to 0.78. The optimal hydraulic performance of stilling basin was noted when wall convergence angle of 2.5° was used along with modified Friction Blocks. Hydraulic performance of modified stilling basin may be investigated during gated operation of the model. HIGHLIGHTS Walls convergence in stilling basin.; Navier–Stokes equations.; Computational Fluid Dynamics (CFD) code.;

Surfactants play a pivotal role in daily life owing to their commendable performance. The outbreak of the COVID-19 pandemic notably escalated surfactant usage. Upon entering building drainage systems with wastewater, surfactants profoundly influence hydraulic performance, an aspect that has garnered limited scholarly attention. This study employs an equally proportioned drainage test device to meticulously examine the variances in physical properties between surfactants, such as sodium dodecyl benzene sulfonate (SDBS) and alkyl ethoxylate-9 (AEO-9), and their repercussions on the hydraulic dynamics of building drainage horizontal main drains. Our findings reveal that the introduction of surfactants leads to the following: (1) an augmentation in water velocity and deposition distances of the solid simulant in the building drainage horizontal main drain with concentrations exacerbating this effect. The deposition distance of the solid simulation surged by up to 527% under experimental conditions compared to no surfactant; (2) there was a suppression of hydraulic jump and full degree of the horizontal main drain, with the concentration amplifying this suppression; and (3) an exacerbation of positive pressure in the horizontal main drain was found with increasing concentration, reaching a staggering 235.3% elevation compared to no surfactant. Moreover, SBDS foam outperformed AEO-9, demonstrating a 17.70–36.04% higher positive pressure in the horizontal main pipes. SBDS exhibits lower starting and ultimate viscosity, along with smaller colloid particle sizes, resulting in a 0.9–2.0% reduction in hydraulic jump and full degree. However, its inferior drag-reduction capability leads to a 17.48–36.44% decrease in the final deposition distances of solid simulant in the building drainage horizontal main drain compared to AEO-9. [ABSTRACT FROM AUTHOR]

Hydraulic jump pressure field analysis is essential to assess slab stability in dissipation basins. This study is aimed to modelling non-dimensional extreme pressure coefficients of the minimum pressure fluctuation (CP−) and maximum pressure fluctuation (CP+) using experimental data with three deep learning (DL) techniques. Pressure coefficients were estimated using Convolutional Neural Network (CNN), Gated Recurrent Unit (GRU), and Long Short-Term Memory (LSTM) methods. For the CP− coefficient related to the tested dataset, the correlation coefficient (CC)=0.894 and Willmott’s index of agreement (WI)=0.944 are achieved using the LSTM model, compared with 0.892 and 0.936 for CNN; and 0.892 and 0.943 for GRU. For the CP+ coefficient, CC=0.910 and WI=0.950 are attained using the LSTM model, compared with 0.903 and 0.941 with CNN; and 0.905 and 0.945 with GRU. The results indicate the excellent performance of the LSTM model for estimating pressure coefficients. With laboratory conditions and the experimental data domain framework used in this study, it is shown that the DL models have been successful for modelling very complex systems. Therefore, DL techniques are recommended for estimating extreme pressure coefficients with a reduction in the need to perform expensive experiments. [ABSTRACT FROM AUTHOR]

Hydraulic jump type stilling basins are the most common hydraulic structures for decreasing the excess kinetic energy of flow and are divided into three types: classical, radial and circular basins. Previous studies have reported that the hydraulic characteristics of flow are more favourable in circular basins than in the other types. Therefore, theoretical/experimental modelling was applied to examine the characteristics of circular hydraulic jumps on adverse-sloped beds in circular stilling basins. The present theoretical model applies the momentum and energy equations to derive equations for the sequent depth ratio and relative energy loss of circular hydraulic jumps and classical hydraulic jumps (CHJs). Analysing the effectiveness of the dominant independent parameters showed that increasing the sequent radius ratio up to 2 and the bed slope up to −5% decrease the sequent depth ratio and length of the circular hydraulic jumps by about 30% and 60%, respectively, whereas the relative energy loss increases by about 30%. In addition to the correlation coefficient, different error functions were determined to analyse the precision of the derived semi-theoretical equations. The present circular stilling basin acts like a plunge pool, having a small water depth for low discharges to have a submerged jet condition, downstream of large dams. [ABSTRACT FROM AUTHOR]

This study employs an explicit scheme of solving the pressure Poisson equation based on the moving particle semi-implicit (MPS) method to simulate forced hydraulic jumps on different slopes. To accurately calculate velocity, a mixed source term is used in the discretized pressure Poisson equation. The mesh-free model is validated to simulate a forced hydraulic jump on a slope, and the free surface and velocity profiles are reproduced. The numerical model is then implemented to simulate the forced hydraulic jumps by varying the channel slope, inlet velocity, and height of the bottom sill. The free surface and velocity profiles in the flows are investigated and the effect on the forced hydraulic jumps by the Froude number and height of the sill are analyzed. The developing process of the hydraulic jumps including developing flow patterns and eddy formation is analyzed. It is found there are four flow stages in the developing process of the flow. [ABSTRACT FROM AUTHOR]

Straits and narrows are the place of intensified turbulent mixing. Deep understanding of the turbulent dynamics at these locations is of crucial importance as it conditions the properties of the water masses flowing in the open ocean. A new extensive field experiment, PROTEVS GIB20, with high frequency measurements has been conducted in the Strait of Gibraltar. It allows us to infer dissipation rates of the turbulent kinetic energy, ϵ, from two consistent methods. The range of ϵ is depicted for the different processes which developed in the vicinity of Camarinal Sill, the main topographic feature of the Strait of Gibraltar. It evidences that the bottom boundary layer, hydraulic jumps and large overturns are the main loci of intensified turbulence reaching 10−3W.kg−1. The variability of the turbulence is mainly controlled by semi‐diurnal, diurnal and fortnightly tidal oscillations. Spatially, the western flank of Camarinal Sill is evidenced as the hotspot for turbulent mixing. We confirm a weak variation of the spatially averaged vertically integrated turbulent dissipation rate. This result needs to be qualified in view of the differentiated impact of the various processes on adjacent water masses. The dynamics of the spring tide directly mix Atlantic and Mediterranean waters, resulting in a large spreading of the T‐S diagram. Plain Language Summary: A recent field experiment, PROTEVS GIB20, was performed in the Strait of Gibraltar in October 2020. This experiment was partly designed to observe the turbulent dynamics of the flow in this region. The Strait of Gibraltar presents an important topographic sill, Camarinal Sill, where the current reaches its maximum value enhancing the turbulent processes. Quantifying the turbulence intensity and the associated mixing that develops there is of crucial importance to understand the impact of small‐scale process on larger/regional scales which is now recognized but remains incompletely understood. Such measurements are necessary to assess the performances of the parametrization use in climate model which to dot represent such small‐scale dynamics. Direct measurements of dissipation rate of turbulent kinetic energy are rare near Camarinal Sill, due to the rough environment and strong maritime traffic. From different methods, we infer time series and spatial averages of the turbulence dissipation rate. We describe the variability of the turbulence, the physical processes involved and the impact on water mass mixing. Key Points: Dissipation rates of TKE are inferred near the Camarinal Sill with maximum values of 10−3 W/kg in the hydraulic jumpThe spatio‐temporal distribution of dissipation rates near Camarinal Sill shows maxima on the western flank in tidal outflowsMixing rates are similar during spring and neap tides except for the Atlantic waters more impacted by spring tide hydraulic jumps [ABSTRACT FROM AUTHOR]

Assessing drag force and Reynolds stresses in turbulent flows is crucial for evaluating the stability and longevity of hydraulic structures. Yet, this task is challenging due to the complex nature of turbulent flows. To address this, physical models are often employed. Nonetheless, this practice is associated with difficulties, especially in the case of high sampling frequency where the inherent randomness of velocity fluctuations becomes mixed with the measurement noise. This study introduces a stochastic approach, which aims to mitigate bias from measurement errors and provide a probabilistic estimate of extreme stress values. To accomplish this, a simple experimental setup with a hydraulic jump was employed to acquire long-duration velocity measurements. Subsequently, a modified first-order autoregressive model was applied through ensemble simulations, demonstrating the benefits of the stochastic approach. The analysis highlights its effectiveness in estimating the uncertainty of extreme events frequency and minimizing the bias induced by the noise in the high-magnitude velocity measurements and by the limited length of observations. These findings contribute to advancing our understanding of turbulent flow analysis and have implications for the design and assessment of hydraulic structures. [ABSTRACT FROM AUTHOR]

Background and Objectives In the past, many studies have been carried out on the hydraulics of slide gate. In addition to flow control and measurement, this structure is used for energy consumption downstream. This structure plays an important role in controlling and regulating the speed downstream of the structure. The supercritical flow passing through slide gates has attracted the attention of researchers due to its high energy dissipation. The high velocity of the flow in the downstream of the hydraulic structures is one of the important issues of water engineering and usually causes damages if there is no control in the downstream. The creation of hydraulic jump is associated with the transformation of supercritical to subcritical flow, and as a result, energy consumption occurs. This phenomenon can be seen downstream of structures such as dams, rapids and gates. So far, successive methods have been used to reduce the kinetic energy of the flow passing through the slide gate, which are discussed below. Among the first researches in this field, the studies of Rajaratnam (1967), Rajaratnam (1968) and Alhamid, (1994) can be mentioned. Daneshfaraz et al. (2022a) investigated the hysteretic behavior of the supercritical flow which occurs with two different flow behaviors under the same hydraulic conditions. The results showed in the primary flow, the amount of these depths indicates the subcritical regime, and in the secondary flow, with the formation of the hysteresis phenomenon in some flow rates, it indicates the supercritical regime. The hysteretic phenomenon has a different effect on the amount of energy consumption depending on the type of flow. Methodology The experiments were performed in a laboratory flume 5 m long, 0.30 m wide, and 0.45 m deep. The laboratory channel has a floor and walls made of Plexiglass and is equipped with a point depth gauge with an accuracy of ±1 mm. A 1 cm thick sluice gate is installed one meter away from the beginning of the flume. In all experiments, the gate opening was considered constant and equal to 5 cm. The discharge applied in the present study ranged from 700 to 900 l/min. The effect of the threshold with semi-cylindrical, cylindrical, pyramidal, and rectangular cube geometric shapes and with different widths of 5, 7, 10, 15, and 20 cm was investigated experimentally. In the present paper, the sill was installed in the different position, including under, the tangential state downstream and upstream of slide gate. Findings The energy dissipation of the sluice gate was investigated in the non-sill mode and with increasing discharge. Laboratory studies showed that the increase in flow rate caused an increase in the flow speed and consequently the descent number of the supercritical region. As a result, the depth of flow in section A has decreased and it has caused energy consumption downstream of the sliding gate. Energy consumption by installing sill in different positions showed that all four geometries, including semi-cylindrical, cylindrical, pyramidal and rectangular cubic sill, had the maximum energy loss in the position under the gate. Results showed that for under gate sill, the maximum of energy dissipation is related to pyramidal, semi- cylindrical, cylindrical and rectangular cubic sills, respectively. The increase in the jetting streamlines due to the application of the pyramid sill is evident in the tangential position downstream of the gate. The results showed that placing circular sills, including semi-cylindrical and cylindrical, in the downstream of the slide gate, cause the uniformity of the flow lines. Therefore, the depth of the flow in the initial section of the hydraulic jump is reduced compared to the polygon sills. Conclusion The results showed that the amount of energy loss increases with the increase in sill width. Due to having the slope of the downstream side in the same direction as the flow, the pyramid threshold increases the speed of the flow and therefore causes a decrease in the initial depth of the flow. Circular sills including semi-cylindrical, cylindrical and rectangular cube were included, respectively, with the greatest initial depth .By changing the position of the threshold to the tangent position downstream of the slide gate, the highest amount of energy loss was assigned to semi-cylindrical, cylindrical, rectangular cube and pyramidal thresholds, respectively. [ABSTRACT FROM AUTHOR]

A sewer system is a principal element of infrastructure in modern cities, accounting for massive amounts of public investments. Corrosion of manholes in the sewer system is a global issue, and millions of dollars are being spent on the maintenance, restoration, and replacement of deteriorated sewer networks. Concrete manholes in the sewer system are deteriorating due to the attack of sulfuric acid produced by microorganisms in a process termed microbial induced concrete corrosion (MICC), which reduces the lifespan of concrete sewer elements. The objective of this paper is to investigate the correlation between the gas- and liquid-phase sewer environmental factors and hydrogen sulfide concentration in the gas phase. The production, emission, and build-up of hydrogen sulfide gas in manholes is identified as a major cause of MICC in manhole shafts. The field study was conducted in more than 200 manholes in the City of Arlington (Texas, US). The data was collected every minute for 48 h to understand the trends of liquid- and gas-phase parameters such as hydrogen sulfide (H2S concentration), liquid and gas temperature, pH, DO, and relative humidity. The study also examines how gas-phase H2S concentrations vary with season; manhole design, including manholes' depth, slope, and presence of drop; and sewer flow conditions such as velocity and turbulence. Although no strong linear correlation was found between liquid-/gas-phase parameters, the manhole categories were found to play a significant role in H2S generation. The manholes with hydraulic jump generated the highest average H2S concentrations, followed by manholes with drops. High turbulence zones were observed in manholes of both categories, leading to H2S stripping from liquid to gas phase. The highest H2S concentration was recorded in summer, suggesting that higher liquid temperature resulted in increased bacterial activity, which generated greater liquid-phase sulfide. Greater Henry's law constants in summer, due to high temperatures, would have favored transfer of liquid-phase sulfide to the gas phase. [ABSTRACT FROM AUTHOR]

One of the main interests of researchers is the local scour downstream hydraulic structures due to free hydraulic jump, which can cause massive damage or collapse for hydraulic structures. In this study, a new countermeasure was developed to reduce the maximum scour depth by using two buried plates and a sill downstream of the sluice gate. The results showed that the two buried plates were a very effective tool in reducing the maximum scour depth downstream of the fixed apron. It was found that when the two plates were buried at (LP1/LB = 0.07 with LP2/LB = 0.14) with a sill installed at (LS/LB = 0.1 with hS/LS = 0.14), the maximum scour depth upstream and downstream of the first plate (Ds1 and Ds2) was reduced by 57% and 64%, respectively, and the maximum scour depth downstream of the second plate (Ds3) was reduced by 35% compared to the maximum scour depth for the no-plate condition. An empirical formula was developed to determine the maximum scour depth. The study results may be applied in the area of protection design for the fixed apron. [ABSTRACT FROM AUTHOR]

In the stilling pool of the spillway and flushing tunnel, there are often problems such as unstable fluctuation range of hydraulic jump and even overtopping the side wall. In order to obtain a good energy dissipation and erosion prevention effect of the stilling pool, the fluid movement during the flood discharge process of the spillway and flushing tunnel was studied through a combination of numerical simulation and physical model testing, which was beneficial for gaining hydraulic dynamics of the flow field and the downstream riverbed erosion conditions . The hydraulic characteristics of water flow under different stilling pool body shape optimization schemes were analyzed, and those schemes were verified by physical experiments. The results show that the flow pattern is more stable under adding a rectangular tailgate at the stilling pool, the water surface fluctuation is reduced. At the same time, the maximum decrease of inlet and outlet velocity in the stilling pool is 7.66 m/s. The pressure distribution is uniform, no negative pressure is generated, and the energy dissipation rate reaches 80.60%. After the addition of the rectangular tailgate, the riverbed scour pit range of the design and verification conditions are reduced by 12.20 m and 13.30 m compared with the original scheme, and it' s maximum scour pit depth are reduced by 0.48 m and 1.00 m compared with the original scheme, respectively. The decrease of the riverbed scour pit range and the maximum scour pit depth shows that the addition of rectangular tailgate has obvious protective effect on the downstream. The research shows that the stilling pool body shape optimization scheme can effectively improve its energy dissipation. The flow field distribution of the optimized stilling pool body shape is uniform, which have great protection on the downstream river bed. The research results can provide reference for diversion and flood discharge and sand flushing projects. [ABSTRACT FROM AUTHOR]

For a thin liquid film (in a supercritical flow) prior to the formation of a non-circular hydraulic jump formed by a round jet obliquely impinging on a horizontal plate, the time-averaged film thickness and the surface wave velocity are extracted based on the measured transient film thickness. On the one hand, the effect of many factors, including the jet velocity, impingement angle, azimuthal angle, liquid viscosity, and surface tension, on the time-averaged film thickness and surface wave velocity are discussed. When the jet Reynolds number increases to about 1.4 × 10 4 , the film thickness profile suddenly increases, and the transition of liquid flow from laminar to turbulent occurs. Meanwhile, a rapid increase is observed downstream of the turbulent film thickness profile. The influence of surface tension on the time-averaged film thickness and surface wave velocity is negligible for thin liquid films before non-circular hydraulic jumps. Nonetheless, the surface tension has a significant influence on the interface profile of non-circular hydraulic jumps. Furthermore, a "crescent" kink region upstream of the jump can be identified when the surface tension is lower than 40.6 mN/m. On the other hand, experimental results are used to verify the prediction accuracy of existing approximate solutions. The laminar approximate solution with a quadratic boundary layer velocity profile can accurately predict the film thickness distribution of most laminar thin liquid films, except downstream of the thin liquid films with a dynamic viscosity higher than 9.71 mPa s. The surface wave velocities are found to be close to the predicted surface velocities of the approximate solutions. [ABSTRACT FROM AUTHOR]

Dam break flows have been a focus of attention for a long in the hydraulic engineering discipline. The interest stems from their high hazard potential to human life and property. This research investigates a laboratory dam break flow using a 3D Reynolds-averaged Navier–Stokes (RANS) and a 2D shallow water Eq. (2D SWE) model. The two numerical models have been compared to measured data regarding flow depth, streamwise surface flow velocity, and point velocity. The results show that as far as a simulation of water depths at gauging stations is concerned, both models are almost at par with an error of about 20% of the mean depth value. Further, the comparison of surface velocity field reveals that though both models are capable of reproducing the salient flow features, e.g., oblique hydraulic jump, wake, etc., the 3D RANS model is more accurate in predicting the jump length and the so-called wet–dry fronts. The important contribution of this research lies in clearly enunciating the tradeoffs between a 2D SWE model and a 3D RANS model. The former model is computationally efficient and accurate as far as flow depth and velocity are concerned while the latter model provides a more complete result output, e.g., vertical flow velocity, turbulent kinetic energy and turbulent dissipation, etc. However, for obtaining significant accuracy with a 3D model a more accurate turbulence model than RANS is required which necessitate usage of very refined mesh (~ mm), thus, raising the cost of the simulation manifold. [ABSTRACT FROM AUTHOR]

Different flow characteristics namely sequent depth ratio, relative height of jump, relative energy loss, efficiency, relative length of jump and relative length of roller in suddenly expanding channel against inflow Froude number varying between 2 to 9 at different expansion ratios B1/B2 (0.4, 0.5, 0.6 and 0.8) as third variable are experimentally studied. Physical explanations of the variation of these characteristics with Froude number are discussed based on the results from experiments. Empirical models are proposed for all the six characteristics for rectangular and suddenly expanding channels using Buckingham π-method which gives quite satisfactory results when compared with other researchers result. Effectiveness of baffle blocks and sills (with different configurations) were also discussed in dissipating maximum energy. Due weightage has been given to Froude and Reynold's number in present study as reported literature as well. As a result, baffle block and sills caused a significant improvement in sequent depth ratio by an amount of 30%, reduction in relative length of jump ratio and relative length of the roller by an amount of 38% and 37% respectively. Hence, energy dissipation increases due to appurtenances. [ABSTRACT FROM AUTHOR]

Weirs are often used in laboratories, industries, and irrigation channels to measure discharge. The discharge capacity of a structure is vital for its safety and plays an important role in the combined gateweir flow, which is a complicated phenomenon in hydropower. This study carried out experiments on a combined hydraulic structure, which included a compound sharp-crested weir made up of two rectangles along with an inverted semicircular sharp gate. Installed on a straight channel, this structure served as a control instrument. The study aimed to investigate the downstream hydraulic jump characteristics of this combined structure, specifically, the sequent depth ratio (y2/y1), the hydraulic jump height ratio (Hj/y1), the energy loss ratio through the jump (EL/Eu), and the jump length ratio (Lj/y1). The width of the upper rectangle on the weir was set at 20 cm. The width of the lower rectangle (W2) was set at 5, 7, and 9 cm, while its depths (z) were fixed at 6, 9, and 11 cm. The gate's diameters varied between 8, 12, and 15 cm. These measurements were alternated with varying initial Froude numbers (Fn1) ranging between 1.32 and 1.5. The results showed that the dimensions of both the weir and the gate influenced the hydraulic jump characteristics. Empirical formulas were developed to predict y2/y1, Hj/y1, EL/Eu, and Lj/y1 based on the differing dimensions of the combined structure. The findings and analysis of this study are limited to the range of data that were tested. [ABSTRACT FROM AUTHOR]

The phenomenon of local scour downstream of irrigation weir energy dissipators is one of the basic degradation problems in hydraulic structures on rivers. The hydraulic jump in the stilling basin, which is triggered by flow turbulence due to energy dampening, forms current vortices in horizontal and vertical directions. Eddy currents that are not fully controlled and damped in the stilling basin can cause scouring, especially in the vertical direction just downstream of the energy dissipators construction. Simultaneous accumulation of scour in the long term can endanger buildings around the weir, especially the stilling basin, both downstream wings and the main weir. This paper aims to assess weir safety by predicting scour characteristics under end sill energy dissipators using the hybrid model: HEC-RAS and Scour Empirical Equation. The simulation is carried out on three conditions, namely minimum, average and maximum discharges with input of sediment grain gradations obtained from field measurements. The three types of discharge are obtained from the transformation of daily rainfall into daily discharge using the HECHMS Model. The results of scour predictions in the 3 scenarios were compared with the results of scour measurements at the study location. The results of the study indicate that the greatest scour depth at the maximum discharge of almost 1.5 meters has reached the depth of the end sill of the energy dissipator. This prediction result was also verified by the observation scour depth of more than 1.5 meters. Observation results also show that the Energy Dissipator II has collapsed massively both in the center and on the left and right sides of the energy dissipator. Based on the results of the study and investigation, it can be concluded that the weir safety at the study location can be categorized as low with the potential for very large scour. [ABSTRACT FROM AUTHOR]

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The present investigation delves into the intricate dynamics surrounding the incorporation of thresholds and their consequential impact on parameters associated with hydraulic jumps—a phenomenon critical to the efficient functioning of the gates. In the pursuit of a comprehensive understanding, the study employed experimental models of thresholds crafted from polyethylene. These models underwent meticulous examination, encompassing variations in dimensions, widths, and positions relative to the gate. The positions explored included beneath the gate, tangent to the gate upstream, and downstream, each contributing unique insights into the behavior of water flow and energy dissipation. An intriguing outcome emerged as thresholds were introduced at different locations. The energy dissipation for a given gate opening exhibited a discernible increase, shedding light on the intricate relationship between threshold placement and hydraulic performance. Notably, as the initial depth relative to the secondary depth increased, a consequential decrease in the ∆EAB/yA was observed, signaling a convergence between the initial and secondary depths. Further illuminating the findings, a comparative analysis of energy loss was conducted across all three threshold positions—beneath the gate, tangent to the gate upstream, and downstream. This scrutiny uncovered a distinct pattern, indicating a heightened energy dissipation in scenarios where the threshold was submerged, setting it apart from conditions where the threshold was positioned otherwise. In essence, the investigation not only accentuates the intricate interplay between sluice gates, thresholds, and hydraulic parameters but also underscores the importance of considering the placement of thresholds in optimizing the energy dissipation efficiency of these hydraulic structures. [ABSTRACT FROM AUTHOR]

The hydraulic jump occurs in open channels and downstream of hydraulic structures because these features change the flow regime from super-critical to sub-critical. To prevent downstream channel erosion and guarantee the construction of a hydraulic jump, a stilling basin is utilized. The effect of sand-roughened beds on hydraulic jump characteristics was investigated using an experimental study. After that, new machine learning models including Emotional neural network (EANN), Hammerstein Weiner model (HWM), Elman neural networks ENN, and Extreme learning neural networks (ELNN) were adopted to estimate the ratio of hydraulic jump length to initial water depth. Different evaluation criteria such as determination Coefficient (R2), Mean Square Error (MSE), Correlation Coefficient (R), and Rout Mean Square Error (RMSE), scatter plots, time series comparison, and Spiral plots have been used to evaluate the models' performance. The results revealed that the Elman NN model outperformed the other models in estimating the ratio of hydraulic jump length to the initial depth (Lj/y1), while the HWM model has a weaker performance than other models in estimating Lj/y1.

The experimental evaluation of the performance of a corrugated apron under free flow subcritical and submerged conditions was conducted, with a focus on scour patterns over the apron. Comparative analysis with a smooth rigid apron revealed an increase in scour depth upon the application of the corrugated apron under free and submerged jet flow conditions. The implementation of a corrugated apron resulted in a considerable reduction in scour depth and length compared to a smooth rigid apron. The maximum reduction in scour depth and length amounted to 79% and 83%, respectively, while the minimum reduction observed was 13% in scour depth and 11% in scour length. Additionally, investigations into velocity and turbulence characteristics over both smooth and corrugated aprons were conducted. It was observed that the rate of turbulence intensity increase within the scour hole due to the presence of a smooth apron surpassed that of the corrugated apron. Scour downstream of the corrugated apron exhibited distinct delineations, including regions of jet diffusion, transition, acceleration, and a recirculating zone near the bed of the scour hole.

Stilling basins are built in conjunction with dams, weirs, and gates to dissipate the high kinetic energy of incoming flow and prevent severe scouring of the downstream riverbed. Dissipation of this high energy can be achieved through forming a hydraulic jump. The hydraulic jump features, including the relative length, ratio of sequent depth, and energy dissipation, are utilized as criteria to evaluate the efficiency of the stilling basin operation. The present study involved conducting experimental and numerical tests to evaluate the performance of the USBR II stilling basin downstream of an ogee spillway using six upstream Froude numbers ranging between 6.37 and 14.97. Experiments were conducted for the Typified USBR II stilling basin. The results were used to perform mesh sensitivity for numerical simulation. The USBRII stilling basin with different rough beds was numerically simulated using FLOW-3D software. The rough beds were designed using three roughness intensities, 10%, 15%, and 22%, and three relative roughness heights: 1, 0.75. and 1. According to the numerical results, distributing staggered cubic elements in the bed of the USBR II stilling basin at 10% intensity and a relative roughness height of (1) enhanced the stilling basin performance compared to the smooth bed and other rough beds. In the case of the best roughness bed, the sequent depth ratio decreased by about 12.1%, and the energy dissipation enhanced by around 5.1% compared to the Typified basin.

Hydropower is an affordable, sustainable way to generate electricity. Research on hydraulic jumps focuses only on determining head loss across the jump, but there are no studies on generating power from the jump. This research aims to utilize energy dissipated from hydraulic jumps for power-generating purposes and further use this power in real-life applications. This research simulates ideal hydraulic conditions to identify the most stable hydraulic jumps, which will be used to generate power. The Seriakos barrage in Egypt was taken as a case study to simulate energy dissipated/power generated from hydraulic jumps generated downstream. This power is then used to simulate lighting up some streets in Egypt according to Egyptian power consumption standards. An Excel spreadsheet was used to mathematically model generated hydraulic jump types, energy dissipated, and generated power. The study found that submerged flow generates maximum power values from hydraulic jumps as opposed to free flow. The research concluded that energy produced by hydraulic jumps at the Seriakos barrage could light up 78 street light bulbs. Although this is a small amount of power, Egypt could meet a significant portion of its energy needs if hydraulic jumps from all its hydraulic structures were utilized for power generation. Doi: 10.28991/HEF-2024-05-01-06 Full Text: PDF

Hydraulic jump is a common physical phenomenon in the field of hydraulic engineering. The essence of hydraulic jump is the conversion and dissipation of a large amount of energy due to the interaction between vortex structures, mainly released in the form of turbulence and water waves. This process significantly reduces the kinetic energy of water flow, thereby mitigating downstream erosion and protecting hydraulic structures, which in turn extends their service life. As a crucial factor in the energy dissipation design of discharge structures, the length of the hydraulic jump is influenced by various factors, including flow velocity, upstream and downstream water depths, riverbed roughness height, and Froude number. In this study, we applied dimensional analysis to identify the key parameters influencing hydraulic jumps on the dataset provided by literature. We utilized a multi-task learning strategy, incorporating a shared feature extraction layer for characteristic modeling of hydraulic jumps within Physics-Informed Neural Networks (PINNs). Furthermore, we compared the performance of PINNs with other data-driven models such as Deep Neural Networks (DNNs), Convolutional Neural Networks (CNNs), and Transformers. The results demonstrated that these models are effective in estimating the length of hydraulic transitions and distinguishing between steady and unsteady hydraulic jump processes. Notably, the PINNs model exhibited better performance than other models, achieving an $\mathbf {R^{2}}$ score of $\mathbf {0.8818}$ , RMSE of 4.4627(cm), MAE of 3.3784(cm), precision of $\mathbf {0.9677}$ and recall of 0.9677 on the test set. These findings are significant for elucidating the characteristics and effects of hydraulic jumps in hydraulic structures, providing a scientific basis for the safe operation and design of practical hydraulic engineering projects.

Different flow characteristics namely sequent depth ratio, relative height of jump, relative energy loss, efficiency, relative length of jump and relative length of roller in suddenly expanding channel against inflow Froude number varying between 2 to 9 at different expansion ratios B1/B2 (0.4, 0.5, 0.6 and 0.8) as third variable are experimentally studied. Physical explanations of the variation of these characteristics with Froude number are discussed based on the results from experiments. Empirical models are proposed for all the six characteristics for rectangular and suddenly expanding channels using Buckingham π-method which gives quite satisfactory results when compared with other researchers result. Effectiveness of baffle blocks and sills (with different configurations) were also discussed in dissipating maximum energy. Due weightage has been given to Froude and Reynold’s number in present study as reported literature as well. As a result, baffle block and sills caused a significant improvement in sequent depth ratio by an amount of 30%, reduction in relative length of jump ratio and relative length of the roller by an amount of 38% and 37% respectively. Hence, energy dissipation increases due to appurtenances.

This study presents a comprehensive dataset comprising multiple data packages derived from laboratory experiments on steady and unsteady hydraulic jumps interacting with a large-scale Gaussian-shaped bed obstacle in an open-channel flume. The primary objective was to accurately measure the impact of hydraulic jump on the free surface and the bed pressure along the obstacle, ensuring the transferability of the results. A multi-process method was followed: designed experiments were recorded, images were postprocessed, and water level data were digitalized. For steady conditions, the bed pressure along the obstacle were measured by piezometers. The repository data are organized and provided in a single package, supplemented by a second package containing panoramas for each experimental time instant and graphical representations of the data, facilitating rapid evaluation of the outcomes. This study provides versatile data that can be utilized in various ways, particularly for fluvial model validation and studying turbulence-driven phenomena in open-channel flows. The detailed methodology presented herein can contribute to the advancement of enhanced laboratory techniques to study similar flow problems. [ABSTRACT FROM AUTHOR]

Sills and baffles are appurtenances used to stabilize hydraulic jump in a stilling basin. The force acting on these appurtenances are characterized by the drag coefficient (CD). This paper describes experimental methods carried out in a rectangular channel to analyze the drag characteristics of sill and baffles in free (unsubmerged) and submerged hydraulic jumps. The sills and baffles were designed as per the USBR type III stilling basin guidelines. A calibrated loadcell connected to an Arduino board was used to measure the drag force. Errors in measurements are limited to 1%. The drag co-efficient was obtained for different Froude numbers (F1=U1/√gy1) pertaining to strong jump (4.5–9) for different relative position of sills (xS/y2) and baffles (xb/y2) from the nozzle of the sluice gate. Both forced (unsubmerged) and submerged jumps were investigated. It is seen that the drag coefficient of appurtenances in submerged jumps were lower than those in free jumps. This may be attributed to the reduction in wake size in submerged jumps. Comparisons of the experimental results of the sill with the previous theoretical studies are reasonable. [ABSTRACT FROM AUTHOR]

Under large unit discharges, stepped chutes are susceptible to cavitation damage due to lack of entrained air. Among various preaeration devices, the simple-structured abrupt contraction aerator (ACA) has a good performance on mild-slope (V:H=1∶5) stepped chutes with a combined flow pattern consisting of a jet and a local hydraulic jump. To advance the understanding of ACA hydraulics, this paper investigates the effects of stepped chute slope and slit location on jet dynamics. A series of physical experiments were carried out on a steep-slope (V:H=4∶5) stepped chute with varied slit locations. It was found that a jet was generated by ACA, and sufficiently aerated flow skimmed over the chute bottom with no black water, indicating an effective reduction of cavitation damage. The slit location had little effect on the flow patterns and aeration but might raise the flow profiles and enlarge the jet. Based on the experimental data, the empirical formulas for maximum height and distance of the jet are finally presented to provide references for sidewall design. [ABSTRACT FROM AUTHOR]

This paper analyzes the dam-break flow propagation over a stair using a novel version of the weakly compressible moving particle semi-implicit method, which was improved with the particle shifting technique and the quintic kernel function. The proposed method was validated with the experimental data of dam-break propagation. The simulation was conducted in two scenarios, in the first of which an obstacle-shaped stair was located in the flow direction, and the collision of the water volume with the stair was modeled through the proposed approach. The results were then compared with those obtained from the finite-volume method (FVM) in STAR-CD. In the second scenario, the dam-break flow descended a stair, reaching the bed and propagating in two directions: toward the right wall and backward near the stair wall. The submerged hydraulic jump was created near the stair wall because the flow did not have enough length to make the conjugation depth. The simulation results from both scenarios were consistent with those of the FVM solver. Furthermore, a quantitative analysis was performed by calculating error norms, resulting in values within the 10–4 range. The analysis indicated a high level of accuracy and consistency between the simulated results and the reference data. In addition, the issue of particle clustering was addressed effectively using the particle shifting approach. [ABSTRACT FROM AUTHOR]

Open-channel flows over a drop structure with a trench, often seen in urban rivers, may cause an oscillating phenomenon of hydraulic jumps depending on the trench geometry and hydraulic conditions. The oscillating hydraulic jumps are accompanied by large-scale water-surface variations with wave breaking, and numerical predictions of such flows are challenging in hydraulics. Using unsteady Reynolds-averaged Navier-Stokes simulations of air-water two-phase flows, we attempted to predict an oscillating hydraulic jump at a drop structure with a trench observed in our laboratory experiment. Several high-Reynolds-number turbulence models were applied, and the effects of turbulence models and grid resolutions on predicting the oscillating hydraulic jump were investigated. Turbulence models other than the k–ω SST model resulted in a steady-state flow with no oscillations regardless of the grid resolution. The k–ω SST model succeeded in predicting the oscillating hydraulic jump using a fine grid while the flow became a quasi-steady state using a coarse grid. Moreover, the period of the oscillation and the flow fields are in good agreement with the experimental results. The k–ω SST model has the ability to predict oscillating hydraulic jumps, including wave breaking, because this model accurately simulates flows with separations or stagnations under adverse pressure gradients. [ABSTRACT FROM AUTHOR]

With ever increasing integration density of electronic components, the demand for cooling solutions capable of removing the heat generated by such systems grows along with it. It has been shown that a viable answer to this demand is the use of direct liquid jet impingement. While this method can generally be scaled to the cooling of large areas, this is restricted by the necessity of coolant flow rate scaling. In this study, the benefits and restrictions of using increased nozzle pitch to remedy the increasing demand for overall flow rate are investigated. To this end, a model is validated against experimental findings and then used for computational fluid dynamics simulations, exploring effects of the pitch change for micro-scale nozzle diameters and nozzle-to-target spacings. It is found that while this method is efficient in adjusting the tradeoff between total coolant flow rate and pressure drop up to a certain pint, the occurrence of a hydraulic jump in the cavity causes a deterioration of its effect for large nozzle pitches. [ABSTRACT FROM AUTHOR]

The hydraulic jump is a natural phenomenon that occurs when the flow transitions from a supercritical flow to a subcritical flow within a short distance. The hydraulic jump is considered one of the most effective methods of dissipating energy through the stilling basin downstream of the control structures. The energy dissipation in the stilling basin contributes to protecting the area downstream of the control structures from erosion which may cause the collapse of the structure. The aim of this study is to calibrate the Flow 3D program using practical experiments. A three-dimensional numerical simulation was performed using the Flow 3D program to investigate the dissipation of energy due to a hydraulic jump through stilling basins with a negative step and compare the results of the study with the results of the practical experiments. (The simulated experiments in this paper using the Flow 3D program were performed at the National Centre for Water Research, Egypt.) It was clear from the comparison that the program has a high ability to simulate the phenomenon and to show results that are close to reality with an error of not more than 10%. [ABSTRACT FROM AUTHOR]

Twin tungsten electrode-wire electrode indirect arc welding (TTW-IAW) is a new welding method, in which the twin tungsten electrodes are connected to the power source together with the welding wire, while the base metal is not connected to the power source, so that the indirect arc is formed between the twin tungsten electrodes and the welding wire. Currently, only the arc characteristics and the droplet transition behavior have been studied, which limits the application of this process in practical welding. In this paper, the thin-plate butt welding process is applied for the first time in TTW-IAW, and the effects of process parameters on weld formation, microstructure, and its hardness are investigated. Additionally, the formation mechanisms of burn-through and hump defects are revealed by the static model and hydraulic jump model of the molten pool, respectively. The results show that TTW-IAW achieves stable weld formation at a maximum welding speed of 600 mm/min, a fourfold increase compared to conventional cold-wire single-TIG welding (conventional cold-wire STW), which reflects its advantages of large deposition rate and high welding efficiency. The degree of influence of the welding current on the penetration of base metal is greater than the welding speed, and the increase in welding current is conducive to the increase in the base metal penetration and the heat-affected zone (HAZ) width, while the increase in welding speed can reduce the convex height of the weld. However, excessive welding currents cause the downward component of arc force and droplet impact to be increased and the upward component of surface tension to be decreased, which results in destabilization of the molten pool, leading to the formation of burn-through defects. Excessive welding speed causes the flow rate of the liquid in the molten pool to be increased and the critical value for the occurrence of a hydraulic jump is exceeded, leading to the formation of a hump. [ABSTRACT FROM AUTHOR]

A high‐resolution model in conjunction with realistic background wind and temperature profiles has been used to simulate gravity waves (GWs) that were observed by an atmospheric radar at Syowa Station, Antarctica on 18 May 2021. The simulation successfully reproduces the observed features of the GWs, including the amplitude of vertical wind disturbances in the troposphere and vertical fluxes of northward momentum in the lower stratosphere. In the troposphere, ship‐wave responses are seen along the coastal topography, while in the stratosphere, critical‐level filtering due to the directional shear causes significant change of the wave pattern. The simulation shows the multi‐layer structure of small‐scale turbulent vorticity around the critical level, where turbulent energy dissipation rates estimated from the radar spectral widths were large, indicative of GW breaking. Another interesting feature of the simulation is a wave pattern with a horizontal wavelength of about 25 km, whose phase lines are aligned with the front of turbulent wake downwind of a hydraulic jump that occurs over steep terrain near the coastline. It is suggested that the GWs are likely radiated from the adiabatic lift of an airmass along an isentropic surface hump near the ground, which explains certain features of the observed GWs in the lower stratosphere. Plain Language Summary: In this study, a high‐resolution computer model was used to simulate atmospheric gravity waves (GWs) that were observed by an atmospheric radar in Antarctica. The simulation successfully reproduced the characteristics of the observed GWs, such as the strength of vertical wind disturbances observed from the ground to 8 km altitude. The simulation showed ship‐wave‐like responses along the Antarctic coast, while, at higher altitudes, the wave pattern changed significantly due to the vertical structure of the background wind. Another interesting finding from the simulation is the presence of a wave pattern with a horizontal wavelength of approximately 25 km. The wavefronts of these waves align with the turbulent region formed downwind of a steep terrain along the coastline. The GWs are likely generated by the uplift of air along a particular type of atmospheric feature near the ground, which explain the upward transport of momentum observed by the radar. Key Points: Numerical simulations of gravity waves (GWs) over Syowa Station, Antarctic, successfully reproduce their amplitudes and momentum fluxesShip‐wave responses along the coastal terrain and wave filtering in the vertical structure of background winds are observedGWs are radiated from the lift of an airmass along an isentropic surface hump associated with a near‐surface a hydraulic jump [ABSTRACT FROM AUTHOR]

In an effort to capture the continuous hydraulic jump and flow structure for a jet impinging on a disk, we recently proposed a composite mean-field thin-film approach consisting of subdividing the flow domain into three distinct connected regions of increasing gravity strength (Wang et al., J. Fluid Mech., vol. 966, 2023, A15). In the present study, we further validate our approach, and examine the characteristics and structure of the circular jump and recirculation. The influence of the disk radius is found to be significant, especially in the subcritical region. Below a disk radius, the jump transits from type Ia to type 0 after the recirculation zone has faded. The supercritical flow and jump location are insensitive to the disk size, but the jump length and height as well as the vortex size are strongly affected, all decreasing with decreasing disk radius, exhibiting a maximum with the flow rate for a small disk. The jump is relatively steep with a strong recirculation zone for a high obstacle at the disk edge. Comparison against the Navier-Stokes solution of Askarizadeh et al. (Phys. Rev. Fluids, vol. 4, 2019, 114002; Intl J. Heat Mass Transfer, vol. 146, 2020, 118823) for the weak and intermediate surface tension suggests that the surface tension effect is unimportant for a high obstacle for a jump of type 0 or type Ia. The film thickness at the disk edge for a freely draining film is found to comprise, in addition to a static component (capillary length), a dynamic component: h∞ ~ (Fr/r∞)2/3 that we establish by minimizing the Gibbs free energy at the disk edge, and, equivalently, is also the consequence of the flow becoming supercritical near the edge. By assuming negligible film slope and curvature at the leading edge of the jump and maximum height at the trailing edge, we show that the jump length is related to the jump radius as LJ ~ Re(Fr²/rJ5)1/3. The vortex length follows the same behaviour. The energy loss and conjugate depth ratio exhibit a maximum with the flow rate, which we show to originate from the descending and ascending branches of the supercritical film thickness. The presence of the jump is not necessarily commensurate with that of a recirculation; the existence of the vortex closely depends on the upstream curvature and steepness of the jump. The surface separating the regions of existence/non-existence of the recirculation is given by the universal relation Re10/3Fr² = 9r∞9/50. The jump can be washed off the edge of the disk, particularly at low viscosity and small disk size. The flow in the supercritical region remains insensitive to the change in gravity level and disk size but is greatly affected by viscosity. [ABSTRACT FROM AUTHOR]