Search

Multi-horizontal submerged jets stilling basins have been utilized in large-scale water conservancy and hydropower projects due to its stable flow pattern, high energy dissipation rate and less atomization. This study employs vorticity criterion, Q criterion, λ2 criterion and Ω criterion to investigate the characteristics of vortex formation and turbulent dissipation in multi-horizontal submerged jets stilling basins with various configurations, including crest overflowing orifice alone (COO), combination of crest overflowing orifice and mid-discharge orifice (COO-MO) and mid-discharge orifice alone (MO). The results indicate that the Q criterion and λ2 criterion are effective in identifying vortex structure within multi-horizontal submerged jets stilling basin. Specifically, the stronger intensity of vortex structure and vortex dissipation are mainly distributed in the vicinity of the vertical drop, which gradually weakens for the increasing distance to the vertical drop. Furthermore, the intensity and number of vortexes with COO-MO are the largest. This conclusion can provide guidance for energy dissipation and bottom protection of stilling pool.

Multi-horizontal submerged jets stilling basins have been utilized in large-scale water conservancy and hydropower projects due to its stable flow pattern, high energy dissipation rate and less atomization. This study employs vorticity criterion, Q criterion, λ2 criterion and Ω criterion to investigate the characteristics of vortex formation and turbulent dissipation in multi-horizontal submerged jets stilling basins with various configurations, including crest overflowing orifice alone (COO), combination of crest overflowing orifice and mid-discharge orifice (COO-MO) and mid-discharge orifice alone (MO). The results indicate that the Q criterion and λ2 criterion are effective in identifying vortex structure within multi-horizontal submerged jets stilling basin. Specifically, the stronger intensity of vortex structure and vortex dissipation are mainly distributed in the vicinity of the vertical drop, which gradually weakens for the increasing distance to the vertical drop. Furthermore, the intensity and number of vortexes with COO-MO are the largest. This conclusion can provide guidance for energy dissipation and bottom protection of stilling pool. [ABSTRACT FROM AUTHOR]

Multi-Horizontal-Submerged Jets are successfully applied to dissipate energy within a large-scale hydropower station. However, notable near-field vibrations are generated when releasing high discharges through the gates, which is generally typical in a flooding case scenario. Under these conditions, the magnitude of the vibrations varies when applying different gate-opening modes. To investigate and find optimized gate-opening modes to reduce the near-field vibration, multiple combinations were tested by varying gate-opening modes and hydraulic conditions. For each of the tests conducted, fluctuating pressures acting on side-walls and bottoms of a stilling basin were measured. The collected datasets were used to determine the maximum and minimum fluctuating pressure values associated with the correspondent gate-opening mode and a detailed comparison between each of the gate-opening modes was completed. The paper presents the quantitative analysis of the discharge ratio’s effect on fluctuating pressures. It also investigates the influence of different gate-opening modes by including side to middle spillways and upper to lower spillways configurations. The flow pattern evolutions triggered by each different gate-opening mode are discussed and optimal configurations that minimize near-field vibrations at high discharges are recommended to support both the design of new systems and assessment of the performance of existing ones.

In the face of depleting fossil energy and the imperative of sustainable development, there is a compelling drive towards advancing renewable energies. In this context, sustainable and predictable alternatives, like marine energy, gain prominence. Marine energy presents a cleaner option devoid of the adverse effects associated with fossil fuels, playing a crucial role in environmental sustainability by safeguarding coastlines against erosion. This study focuses on Astara Port in the Caspian Sea, exploring the utilization of wave energy converters (WECs). The originality of this study's research lies in exploring WECs' dual role in energy generation and coastal protection. Using MIKE21 software simulations, the impact of number, location, arrangement, and orientation of WECs across various scenarios was investigated, including two WEC number scenarios (11 and 13), three structural placement scenarios (north, front, and south of the port), two structural arrangement scenarios (linear and staggered), two port layout scenarios (original layout and modified layout), and two orientation scenarios for the structures (facing north-east, which is the dominant wave direction, and facing southeast). The results show a remarkable decrease in the significant wave height behind WECs, notably with 13 staggered devices facing dominant waves (from northeast), reducing the significant wave height Hs by 23–25%. This setup also shows the highest wave height reduction, notably 36.26% during a storm event. However, linear WEC setup offers more extensive coastline protection, covering 47.88% of the model boundary during storms. Furthermore, the 11 staggered WECs facing southeast (SE) arrangement had the lowest sediment accumulation at 0.0358 m over one year, showing effective sedimentation mitigation potential. Conversely, the 13 linear WECs facing northeast (NE) had the highest accumulation at 0.1231 m. Finally, the proposed port design redirects high-velocity flow away from the port entrance and removes rotatory flow, reducing sediment accumulation near the harbor entrance. [ABSTRACT FROM AUTHOR]

A block ramp is a grade-control structure commonly used to stabilize the river bed with a high efficiency of energy dissipation. This study investigates the effects of using macro roughness and a downstream apron as scour countermeasures on the maximum scour depth downstream of block ramps in straight rivers. All the experiments have been carried out in a horizontal channel and in clear water conditions (no sediment transport). A wide range of hydraulic conditions including densimetric Froude numbers, water drop heights, and tailwater depths for three different rough ramp slopes (1 V:3 H, 1 V:5 H, and 1 V:7 H) was tested. The results have been compared with the results from a smooth ramp (no roughness), which has been considered as a reference. Results show that both macro roughness on the ramp and downstream aprons work well as scour countermeasures while as a comparison, using macro roughness (big-size stones) on the ramp is more effective than downstream aprons to reduce the scour depth. The other finding of this study shows that increasing the downstream apron decreases the length of the scour hole, consequently decreasing the volume of eroded material. [ABSTRACT FROM AUTHOR]

Attention as a cognition ability plays a crucial role in perception which helps humans to concentrate on specific objects of the environment while discarding others. In this paper, auditory attention detection (AAD) is investigated using different dynamic features extracted from multichannel electroencephalography (EEG) signals when listeners attend to a target speaker in the presence of a competing talker. To this aim, microstate and recurrence quantification analysis are utilized to extract different types of features that reflect changes in the brain state during cognitive tasks. Then, an optimized feature set is determined by employing the processes of significant feature selection based on classification performance. The classifier model is developed by hybrid sequential learning that employs Gated Recurrent Units (GRU) and Convolutional Neural Network (CNN) into a unified framework for accurate attention detection. The proposed AAD method shows that the selected feature set achieves the most discriminative features for the classification process. Also, it yields the best performance as compared with state-of-the-art AAD approaches from the literature in terms of various measures. The current study is the first to validate the use of microstate and recurrence quantification parameters to differentiate auditory attention using reinforcement learning without access to stimuli. [ABSTRACT FROM AUTHOR]

Model experiments were conducted on the hydraulic characteristics of air-water two-phase flow inside the bottom outlet of shaft spillways as a result of natural air suction from air-core vortices at the pipe intake. Experiments were performed in a cylindrical reservoir 2 m in diameter and 1 m high, under a swirling flow around the intake, investigating the most severe two-phase flow regimes. Three different vertical pipe intakes, attached to the floor of the reservoir at its centre, were examined for different flow discharges, establishing different vortex types. Results indicate that the void fraction decreases by changing the type of swirling flow. For a constant submergence depth, reducing the intake pipe diameter or increasing its height led to an increase in void fraction and two-phase slug flow wave velocity, length and frequency. However, by the increase in Kolf number, the frequency of slug waves reduced and the two-phase flow pressure inside the bottom outlet was increased. The relationships between two-phase flow hydraulic characteristics and regimes inside the bottom outlet and types of vortices at the intakes will be of interest to both scientific research and design engineers, to increase the efficiency and safety of pressurised waterway systems. [ABSTRACT FROM AUTHOR]

Multi-Horizontal-Submerged Jets are successfully applied to dissipate energy within a large-scale hydropower station. However, notable near-field vibrations are generated when releasing high discharges through the gates, which is generally typical in a flooding case scenario. Under these conditions, the magnitude of the vibrations varies when applying different gate-opening modes. To investigate and find optimized gate-opening modes to reduce the near-field vibration, multiple combinations were tested by varying gate-opening modes and hydraulic conditions. For each of the tests conducted, fluctuating pressures acting on side-walls and bottoms of a stilling basin were measured. The collected datasets were used to determine the maximum and minimum fluctuating pressure values associated with the correspondent gate-opening mode and a detailed comparison between each of the gate-opening modes was completed. The paper presents the quantitative analysis of the discharge ratio's effect on fluctuating pressures. It also investigates the influence of different gate-opening modes by including side to middle spillways and upper to lower spillways configurations. The flow pattern evolutions triggered by each different gate-opening mode are discussed and optimal configurations that minimize near-field vibrations at high discharges are recommended to support both the design of new systems and assessment of the performance of existing ones. [ABSTRACT FROM AUTHOR]

Hydraulic structures, such as barrages, play an important role in the sustainable development of several regions worldwide. The aim of this novel study is to identify the critical hydraulic parameters (CHPs) of Taunsa Barrage, built on the Indus River. These CHPs, including free surface profiles, flow depths, Froude number, velocity profiles, energy dissipation and turbulence kinetic energy, were investigated using simulation via FLOW-3D numerical models. Incompressible Reynolds-averaged Navier–Stokes (RANS) equations on each computational cell were solved using the numerical methods available in FLOW-3D. The simulation results indicated that the locations of hydraulic jumps (HJs) were lower than that were reported in the previous one-dimensional study. Similarly, the distances of the HJs from the downstream toe of the glacis were reached at 2.97 m and 6 m at 129.10 m and 130.30 m tailwater levels, respectively, which deviated from the previous studies. In higher tailwater, the sequent depth ratio also deviated from the previous data. The maximum turbulent kinetic energies were observed in the developing regions of HJs, which were found to be decreased as the distance from the HJ was increased. The results of this research will be highly useful for engineers working in the field of design of hydraulic structures. [ABSTRACT FROM AUTHOR]

A ski jump is one of the most commonly used methods for energy dissipation. However, if the local terrain at where a dam is being built is narrow, the jet takes off from a traditional flip bucket may impact the downstream bank slope directly, endangering the stability of the mountain and the safety of the structure. Therefore, optimization of the design of the flip bucket to make the jet stretch along the river channel longitudinally and conform to the main channel is often needed. The Shiziya dam is such a case, with steep hills, narrow river valleys, and a large bend in lower river. To adjust the flow trajectory in air, a new ski jumping takeoff mode, namely the oblique cut bucket together with liner deflectors on both sidewalls, was innovatively adopted. The FLOW-3D software is used to investigate the hydraulic performance of oblique cut bucket and optimize its layout. The simulation performance is verified using a generalization model experiment. It can be known from the above results, the oblique cut bucket can effectively control the flow direction and longitudinal stretch length of the jet in the air to uniform the jet to the downstream main channel. This is mainly achieved by adjusting the deflection angle, takeoff angle and inclined cutting direction of the side walls of the spillway. [ABSTRACT FROM AUTHOR]

Various methods exist to stabilize asymmetric hydraulic jumps occurring in suddenly expanding channels. In this study, the effects of the interaction of multiple submerged counter flow jets are investigated experimentally in terms of the hydrodynamic characteristics of the flow resulting in the tailwater channel. To this aim, three-dimensional flow velocities downstream of the jet system were measured for different configurations of the device. The stability in the performance of the dissipation system under variable tailwater conditions was analyzed in terms of flow velocity distribution, turbulent kinetic energy, turbulence intensity and Reynolds shear stresses. The results reveal the good performance of the investigated system in preventing the phenomena of flow instability associated with suddenly expanding channels. [ABSTRACT FROM AUTHOR]

The horizontal submerged jet (HSJ), as a special form of jet, is widely used in aerospace, food and drug, water engineering, and other industries. In order to further understand the mechanism of the HSJ, the Wray–Agarwal turbulence model was used to predict the HSJ with different incidence heights H/D and Reynolds number (Re) conditions in this paper. The results show that the jet horizontal height H/D has a large influence on the flow field structure. The unsteady flow within the flow field is dominated by vortexes. In addition, their distribution is relatively independent of H/D. Under different H/D conditions, the axial velocity distribution of the jet has very high similarity, all of them have an obvious velocity inflection point at x = 10D. When H/D is small, the wall attachment effect of the jet and the boundary layer effect generated at the bottom of the fluid domain have a certain role in maintaining the velocity of the jet near the wall, resulting in a significantly higher axial velocity than other H/D conditions, up to 1.29 times. In this paper, we thoroughly investigated the structure of the internal flow field and velocity distribution of the submerged horizontal jet. The results have a guiding significance for engineering practice and academic research. [ABSTRACT FROM AUTHOR]

In this study, the effect of the structure geometry, the bed material, and the river hydraulic conditions on the scour morphology downstream of the stepped-baffle weirs are experimentally investigated. All experiments are conducted in clear water conditions (no sediment transport). Results show, that in the presence of stepped-baffle weirs, the maximum scour depth diminishes with respect to the simple stepped weirs (no baffle) highlighting that increasing the tailwater depth, decreases the maximum scour depth, and decreasing the structure slope, decreases the maximum scour depth. By means of dimensional analysis and incomplete self-similarity, a formula is proposed to predict the maximum scour depth downstream of a stepped-baffle weir considering all aspect ratios of the structure geometry. [ABSTRACT FROM AUTHOR]

In this study, the effects of geometric parameters, such as the ramp roughness size and the ramp slope on the scour parameters downstream of block ramps, are experimentally investigated for different hydraulic conditions. Scour parameters, such as the maximum scour depth and length and the maximum ridge height and length, are evaluated. Experiments are conducted in clear water conditions (no sediment transport) for different gravel ramp slopes in which different critical flow depths and tailwater depths are examined. The results indicate that the maximum scour depth downstream of a block ramp for different bottom slopes is directly affected by the tailwater depth, independent of the critical flow depth; the scour depth decreases by increasing tailwater depth. A comparison of the results indicates that increasing the roughness of the block ramp leads to a reduction in the maximum scour depth. [ABSTRACT FROM AUTHOR]

Roughness recognition is an important function in the nervous system that facilitates our interactions with the environment. Previous studies have focused on the neuro-cognitive aspects and frequency-based changes in response to the roughness stimuli. In this study, we investigate the effect of different roughness levels on the nonlinear characteristics of EEG signals. Nine healthy subjects participated in the current research and touched three surfaces with different levels of roughness in a passive dynamical way. The experiment was repeated for both hands separately. During the experiment, the EEG signals were recorded. Next, three nonlinear features were extracted using the recurrence quantification analysis (RQA) method; and four classifiers were hired to distinguish six conditions, including three levels of roughness and the touching hand. The results showed that EEG nonlinear characteristics were significantly affected by the variation of surface roughness. The effects were different between touching by the left or the right hand. Moreover, it was observed that employing the RQA-based features leads to the higher accuracy of classification compared to the conventional frequency-based features. Additionally, we found that the brain representation of tactile roughness has a pseudo-random dynamic, and the amount of roughness can influence a network of brain channels. Finally, utilizing the weighted combination of different brain channels while considering the extracted nonlinear features, the LDA classification accuracy was reached 93%. Therefore, it can be suggested that not only temporal variations of brain signals but also their spatial distribution (brain channels) are important to recognize the surface roughness. [ABSTRACT FROM AUTHOR]

Upstream and downstream ground vibrations induced by flood discharge of high dams potentially cause damage in surrounding buildings and affect the living quality of local populations. Significant ground vibrations and some structural damages have been reported in the downstream area of Xiangjiaba Dam, a large-scale high dam located on Jinsha River, Yunnan, China. To study the characteristics of downstream vibration, a physical hydroelastic model is built to simulate discharge conditions and dynamic characteristics of the Xiangjiaba Dam. Hydroelastic models are traditionally built without special vibration isolation process; however, significant effects of ambient vibrations are observed. Therefore, a vibration isolation system has been built to reduce the effects of background vibration, including isolation trench, flexible connections, reinforced concrete foundation, and reasonable arrangement of water circulation system. High correlation coefficients are observed between hydroelastic model simulation and field measurements, which verifies the effectiveness of simulating the original discharge conditions using the hydroelastic model. Then a prediction model is created to predict downstream field measurements using model simulation data. The predictions generally agree with field observations well. Vibration energy distribution is analyzed among different structural components, which shows that orifices always have the highest energy contribution, and guide walls have significantly higher contribution when discharging through surface orifices. Furthermore, additional influential factors are studied which shows downstream vibrations generally increase with larger orifices openings, higher upstream water levels, and larger rate of flow. [ABSTRACT FROM AUTHOR]

The article proposes a partial flaring gate pier (FGP) scheme to intensify the energy dissipation inside a conventional stilling basin. Topics discussed include secondary hydraulic jump, vertical vortex, and deep tailwater. Also mentioned are the volume of fluid (VOF) method for the computation of the free space, numerical model implementation, and boundary conditions and initial conditions.

Recurrence plot analysis is a well-established method to analyse time series in numerous areas of research. However, it has exponential computational and spatial complexity. As the main result of this paper, a technique for the computation of recurrence quantitative analysis (RQA) is outlined. This method significantly reduces spatial complexity of computation by computing RQA directly from the time series, optimizing memory accesses and reducing computational time. Additionally, parallel implementation of this technique is tested on the Salomon cluster and is proved to be extremely fast and scalable. This means that recurrence quantitative analysis may be applied to longer time series or in applications with the need of real-time analysis. [ABSTRACT FROM AUTHOR]

Froude number similarity has been used in all the physical experiments of earthquake induced hydrodynamic forces acting on deep water bridge piers without validation. This study focuses on the validation of the viability of Froude number similarity experimentally and numerically. Results show that Froude number similarity is viable, although the gravity wave force does not dominate the hydrodynamic force on bridge piers under earthquakes. Further, Euler number similarity is proven to be viable and Froude number similarity is proven to be the special case of Euler number similarity when λf=λL-1/2(λf and λL indicate frequency scale and length scale respectively) in Euler number similitude. Numerical studies of the application demonstrate both Froude number similarity and Euler number similarity have almost the same precision when they are used to scale up the in-line force of model pier to prototype pier under ordinary earthquakes. However, Euler number similarity is recommended because of the advantages of providing a chance to choose frequency scale, which may be better supported by equipment and allow a Reynolds number closer to the one observed in the prototype. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Near-field drastic vibrations caused by flood discharges have a serious impact on nearby residents and can damage buildings. A novel energy dissipator was invented to solve the technical challenge of energy dissipation in the Xiangjiaba Dam project, a giant hydraulic project in China. However, since this project is located near civil buildings, the obvious near-field vibrations at the wake of first-time flood release have become a serious threat for the surrounding residents and need to be solved urgently. Focusing on hydraulic experiments combined with prototype observations, an effective method was proposed to investigate the responsive relationship between discharge floods and vibrations. In the model experiments, 138 cases were carried out under different combinations of discharge and gate-opening modes. During the experiments, fluctuating pressures acting on the structures were measured; 226 cases were tested in the prototype and the corresponding ground acceleration was measured; the relationship between the root-mean square (RMS) of fluctuating pressure and discharge was obtained. Furthermore, based on the prototype observations, the correlation formula between the acceleration of near-field vibrations and discharge was also proposed. Consequently, the study shows that the prediction of acceleration in near-field vibrations is acceptable and the proposed method can be used to study the near-field vibrations induced by flood releases. [ABSTRACT FROM AUTHOR]

Considering the limitations of unit discharge for stepped chutes, a ski-jump-step energy dissipater, which is a new type of energy dissipater, is first proposed for increasing the maximum available unit discharges. In this system, preaerations are achieved through jets generated by ski-jumps and further aerations are achieved via aeration basins. It provides fully aerated flows for the stepped chutes with large unit discharges, and the problems caused by high-speed flows like energy dissipation, cavitation, and atomization are well solved. Experimental investigations about hydraulic characteristics of the ski-jump-step energy dissipater were conducted, including the flow regimes, the principle and effectiveness of energy dissipation and the characteristics of the air entrainment and the pressure distribution. Even under conditions of large unit discharges (q = 118.00 m2/s on the prototype), results obtained demonstrate energy dissipation as high as 75.8% and air concentrations of at least 3.6% along the whole stepped chute. The method developed herein provides a new approach for energy dissipation in stepped chutes at large discharges. [ABSTRACT FROM AUTHOR]

High-speed diffuse flow is a commonly complex process in tunnels with full-section aerators and lateral expansion walls. The transformation of pressure is prone to produce cavitation on the lateral expansion walls downstream of an aerator. The expansion threatens the stability of the structure and can cause damage. In this paper, the diffuse flows downstream of a radial sluice and full-section aerator were studied by combining a realizable k - ε turbulent model with a mixture multiphase model. Hydraulic characteristics such as pressure distribution and cavitation were investigated. The relationship among pressure, cavitation index, lateral divergence angle α, and Froude number F were proposed. Empirical formulas were presented to calculate and evaluate the pressure and cavitation index on side walls. The calculated results agree well with the physical model. With decrease in divergence angle, pressure increases gradually so that the flow cavitation index increases as well. Profiles of gate openings demonstrated gradual improvement in pressure and cavitation index with an increase in the magnitude of the gate opening. The studies showed that the degree of gate opening has a great effect on the pressure and flow cavitation index of side walls. The lateral expansion and partial gate-opening increased the risk of cavitation erosion on side walls downstream of the radial sluice. Research results provided a reference for optimizing the design of similar engineering. [ABSTRACT FROM AUTHOR]

Flip buckets are commonly used to discharge flow away from a hydraulic structure into the downstream to dissipate energy. A new leak-floor flip bucket is presented, making the ski-jump water jet a typical long-narrow nappe. Based on the model experiments and numerical simulation, the flow pattern, formation process and mechanism of the leak-floor flip bucket are studied. The results show that cross section flow shape develops from the 'Y-type' to '|-type', and this is because the natural pressure difference is generated when water flows through the leak-floor area and moves transversely from both sides to the center. Different from the slit-type flip bucket with sidewall contraction, the leak-floor flit bucket makes the water jet narrow and long without high pressure on the side walls of the flip bucket. Under the same jet length condition, the maximum sidewall pressure of the slit-type is 4.67 times that of the leak-floor flip bucket. The effects of flow discharge on the jet length are less significant for the leak-floor bucket than for the slit-type bucket. [ABSTRACT FROM AUTHOR]

Stepped spillways have a wide range of applicability as a hydraulic structure in large dams to dissipate energy of high-velocity flows at a downstream area of dams as well as release overflows into the downstream. In this study, the numerical simulation of the flow over the stepped spillway was investigated by using Flow3D software as an analytic flow field. The RNG k-ε model was applied as the turbulence model, and Volume of Fluid (VOF) model was used to determine the free surface flow profiles. At the first stage, the model was verified by reliable experimental data. Then, in order to investigate the various features of skimming flow regime, 112 numerical spillway models was designed, which 96 models were stepped spillway models and 16 models were smooth spillway models (i.e., WES profile). In these numerical experiment, two step sizes, six configuration, four passing discharge and four profile slopes (15, 30, 45 and 60 degrees) with various relative discharges were considered to investigate the energy dissipation and discharge coefficient rates. The results indicated that discharge coefficient rate and energy dissipation rate have inverse relationship. Also it was observed that when relative discharges increased, energy dissipation rate decreased and discharge coefficient rate increased. [ABSTRACT FROM AUTHOR]

Vortex drop shaft (VDS) spillways are eco-friendly hydraulic structures used for safely releasing flood. However, due to the complexity of the three-dimensional rotational flow and the lack of suitable measuring devices, current experimental work cannot interpret the flow behavior reliably inside the VDS spillway, consequently experimental and CFD study on a VDS spillway with an elliptical tangential inlet was conducted to further discern the interior three-dimensional flow behavior. Hydraulic characteristics such as wall pressure, swirl angle, annular hydraulic height and Froude number of the tapering section are experimentally obtained and acceptably agreed with the numerical prediction. Results indicated that the relative dimensionless maximum height of the standing wave falls off nearly linearly with the increasing Froude number. Nonlinear regression was established to give an estimation of the minimum air-core rate. The normalized height of the hydraulic jump depends on the flow phenomena of pressure slope. Simulated results sufficiently reveal the three-dimensional velocity field (resultant velocity, axial velocity, tangential velocity and radial velocity) with obvious regional and cross-sectional variations inside the vortex drop shaft. It is found that cross-sectional tangential velocity varies, resembling the near-cavity forced vortex and near-wall free vortex behavior. Analytic calculations for the cross-sectional pressure were developed and correlated well with simulated results. [ABSTRACT FROM AUTHOR]

A stilling basin with sudden enlargement and bottom drop leads to complicated hydraulic characteristics, especially a fluctuating pressure distribution beneath 3D spatial hydraulic jumps. This paper used the large eddy simulation (LES) model and the TruVOF method based on FLOW-3D software to simulate the time-average pressure, root mean square (RMS) of fluctuating pressure, maximum and minimum pressure of a stilling basin slab. Compared with physical model results, the simulation results show that the LES model can simulate the fluctuating water flow pressure in a stilling basin reliably. The maximum value of RMS of fluctuating pressure appears in the vicinity of the front of the stilling basin and the extension line of the side wall. Based on the generating mechanism of fluctuating pressure and the Poisson Equation derived from the Navier–Stokes Equation, this paper provides a research method of combining quantitative analysis of influencing factors (fluctuating velocity, velocity gradient, and fluctuating vorticity) and qualitative analysis of the characteristics of fluctuating pressure. The distribution of fluctuating pressure in the swirling zone of the stilling basin and the wall-attached jet zone is mainly affected by the vortex and fluctuating flow velocity, respectively, and the distribution in the impinging zone is caused by fluctuating velocity, velocity gradient and fluctuating vorticity. [ABSTRACT FROM AUTHOR]

The main objectives of the present work are to investigate the hydraulic characteristics of the dam discharge flow and its impact downstream. Building information modeling technology is adopted to generate the terrain entity and hydraulic structures. The calculation of the dam discharge and flood routing simulation is achieved by employing Reynolds-Averaged Navier-Stokes equations with the RNG k-ε eddy viscosity model for its turbulence closure, as well as the Volume of Fluid method. An urban flood experiment and the field measurement records are utilized and validated the model accuracy. The flow field is obtained to assess the dam working conditions under different water levels. The results show that the maximum downstream flow depth, the maximum discharge capacity and the hydraulic jump length under normal water level is 18.6 m, 13,800 m3/s, and 108 m, respectively. The dam satisfies the safety demand under different water levels but close attention should be paid to the dam foundation, especially around the incident points of the discharge flow. Complex turbulent flow patterns, including collision, reflection, and vortices, are captured by three-dimensional simulation. The numerical simulation can assist the reservoir management vividly, so as to guarantee the stability of the dam operation. [ABSTRACT FROM AUTHOR]

The present study examines the configuration of an offset jet issuing into a narrow and deep pool. The standard k-ε model with volume-of-fluid (VOF) method was used to simulate the offset jet for three exit offset ratios (OR = 1, 2 and 3), three expansion ratios (ER = 3, 4 and 4.8), and different jet exits (circular and rectangular). The results clearly show significant effects of the circumference of jet exits (Lexit) in the early region of flow development, and a fitted formula is presented to estimate the length of the potential core zone (LPC). Analysis of the flow field for OR = 1 showed that the decay of cross-sectional streamwise maximum mean velocity (Um) in the transition zone could be fitted by power law with the decay rate n decreased from 1.768 to 1.197 as the ER increased, while the decay of Um for OR = 2 or 3 was observed accurately estimated by linear fit. Analysis of the flow field of circular offset jet showed that Um for OR = 2 decayed fastest due to the fact that the main flow could be spread evenly in floor-normal direction. For circular jets, the offset ratio and expansion ratio do not affect the spread of streamwise velocity in the early region of flow development. It was also observed that the absence of sudden expansion of offset jet is analogous to that of a plane offset jet, and the flow pattern is different. [ABSTRACT FROM AUTHOR]

Spillway outlet design is a major issue in hydraulic engineering with high head and large discharge conditions. A new type of design for a streamwise-lateral spillway is proposed for ski-jump flow discharge and energy dissipation in hydraulic engineering. The water in the spillway outlet is constrained by three solid walls with an inclined floor, a horizontal floor on the bottom and a deflected side wall in the lateral direction. The water flow releases in a lateral direction into the plunge pool along the streamwise direction. It generates a free jet in the shape of "∩" in a limited area, causing the water to fully diffuse and stretch in the air simultaneously, and drop into the plunge pool to avoid excessive impact in the plunge pool. The formation mechanism for the flow pattern is analyzed, and the results show that the optimum inclination is an angle range of 30°~45° for a good performance of free ski-jump jet diffusion shape. [ABSTRACT FROM AUTHOR]

A new type of vortex drop shaft without ventilation holes is proposed to resolve the problems associated with insufficient aeration, negative pressure (Unless otherwise specified, the pressure in this text is gauge pressure and time-averaged pressure) on the shaft wall and cavitation erosion. The height of the intake tunnel is adjusted to facilitate aeration and convert the water in the intake tunnel to a non-pressurized flow. The hydraulic characteristics, including the velocity (Unless otherwise specified, the velocity in this text is time-averaged velocity), pressure and aeration concentration, are investigated through model experiment and numerical simulation. The results revealed that the RNG k-ε turbulence model can effectively simulate the flow characteristics of the vortex drop shaft. By changing the inflow conditions, water flowed into the vertical shaft through the intake tunnel with a large amount of air to form a stable mixing cavity. Frictional shearing along the vertical shaft wall and the collisions of rotating water molecules caused the turbulence of the flow to increase; the aeration concentration was sufficient, and the energy dissipation effect was excellent. The cavitation number indicated that the possibility of cavitation erosion was small. The results of this study provide a reference for the analysis of similar spillways. [ABSTRACT FROM AUTHOR]