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This paper investigates hydraulic jumps in sloping pipes by means of wall-resolved large eddy simulation (LES). The purpose is to achieve an improved understanding of jump behaviours driven by pipe discharge and slope. The LES model predicts the hydraulic jump as a 3-D two-phase flow, with air as the gas phase and water as the liquid phase. The predictions yield instantaneous velocity and pressure fields as well as fluid volume fraction. The instantaneous flow variables allow ensemble averages, which quantify the internal structures and integral properties of the hydraulic jump. The predicted instantaneous velocity shows spectra in consistency with the well-known Kolmogorov −5/3 law. The ensemble averages of air and water velocities, free-surface profile, roller length and aeration length, compare well with available experimental data. The jump behaviours are complex. Some aspects such as free-surface fluctuation and jump-toe oscillation resemble the classical hydraulic jump on horizontal floors. Others like the 3-D distributions of core jet, vorticity and aeration are much more complicated. Depending on the pipe discharge and slope, the resulting jump can be a complete or an incomplete jump. The incomplete hydraulic jump causes choked flow downstream. This has severe consequences on drainage conditions in sewer pipes laid on sloping terrain. This paper proposes using the Okubo-Weiss parameter as a new way to subtly delineate the region of hydraulic jump. It is much more efficient and less ambiguous, compared with traditional visual inspections. [ABSTRACT FROM AUTHOR]

The study of hydraulic jumps in compound rectangular channels has been the subject of several featured contributions. For hydrotechnical structures such as dams, this type of channel has been used in the design of energy dissipation basins to control the downstream flow discharge. In irrigation canals, this technique has presented a technical and economic advantage, especially in low-water periods where flow discharge has been widely exploited. The main objective of this research is to find ways to exploit this configuration of the jump in future hydraulic designs. The present study is based on the experimental analysis of the hydraulic jump characteristics controlled by a thin sill evolving in a compound rectangular channel. This type of jump has been widely studied, and the current work focuses on the classical hydraulic jump. Therefore, through this experimental contribution, the sill effect on the jump characteristics was analyzed. Moving the sill upstream caused jump compactness, defined by the length of the classical roller ratio and the geometric position of the sill. This phase of the flow leads to several jump configurations. To achieve this objective, two cases were presented. In the first case, the flow takes place at the level of the minor bed of the channel with low Froude numbers. In the second case, the jump was formed at the level of the major bed where the Froude numbers are high. The jump compactness ratio was calculated in dimensionless terms as a function of the Froude number and the jump surface profile. [ABSTRACT FROM AUTHOR]

Energy dissipators, such as stilling basins, are usually required at the toe of stepped chutes to achieve adequate and safe operation of the spillway. Stepped chute hydraulics has been extensively studied in last several decades, however, only limited knowledge is available on the stilling basin performance below stepped chutes. In particular, the effect of the chute slope remains unknown, despite being a central design issue. Therefore, an experimental campaign was performed using a 30° or 50° inclined smooth or stepped chute with an adjacent conventional plain stilling basin. The experimental results indicated that, within the stilling basin, the surface characteristics and the roller as well as hydraulic jump lengths are practically independent of the chute slope. This further strengthens the previous findings that stepped chutes require 17% longer dimensionless jump lengths and consequently stilling basin lengths. The experimental results also confirmed that stepped chutes generated increased extreme and fluctuating bottom pressure characteristics at the stilling basin entrance area. With increasing chute slope, the latter were found to significantly magnify. However, such increased magnitudes were not expected to provoke cavitation damage as stepped chute inflows induced bottom aeration at the basin entrance, irrespective of the chute slope. [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to investigate the upstream environment's impacts on the airflow over the lee slope of the Cuyamaca Mountains (CM) near San Diego, California, during the Cedar Fire that occurred from 25 to 29 October 2003. The upstream environment was largely controlled by a southwest–northeast-oriented upper-tropospheric jet streak that rotated around a positively tilted ridge within the polar jet stream. Three sequential dynamical processes were found to be responsible for modifying the mesoscale environment conducive to low-level momentum and dry air that sustained the Cedar Fire. First, the sinking motion associated with the indirect circulation of the jet streak's exit region strengthened the midtropospheric flow over the southern Rockies and the lee slope of the Sawatch and San Juan Ranges, thus modestly affecting the airflow by enhancing the downslope wind over the CM. Second, consistent with the coupling process between the upper-level sinking motion, downward momentum transfer, and developing lower-layer mountain waves, a wave-induced critical level over the mountain produced wave breaking, which was characterized by a strong turbulent mixed region with a wind reversal on top of it. This critical level helped to produce severe downslope winds leading to the third stage: a hydraulic jump that subsequently enhanced the downstream extent of the strong winds conducive to the favorable lower-tropospheric environment for rapid fire spread. Consistent with these findings was the deep-layer resonance between the mountain surface and tropopause, which had a strong impact on strengthening the severe downslope winds over the lee slope of the CM accompanying the elevated strong easterly jet at low levels. [ABSTRACT FROM AUTHOR]

In this study, the SCVW (a novel type of Sharp-Crested V-notch weirs) is employed for more experimentally and theoretically investigations. The length of the hydraulic jump at downstream of the SCVW (LjSCVW) is measured via new supplementary experimental datasets via most popular vertex angles θ (128° and 60°). The experiments are conducted under aerated, steady, and free overflow conditions in an open channel for large physical models. To assess the variations of LjSCVW versus the θ, extensive laboratory work is performed at different discharges (Q), diverse triangular segments number (Nst) in the SCVW, and various tailgate angles (ɸ). Via dimensional analysis and pre-processing method, most effectual parameters on the LjSCVW were obtained as Fr1 (approaching Froude number), Re1 (incoming Reynolds number), and y 2 y 1 (relative sequent depths). Based on the experimental results, by increasing the values of Fr1 and Re1, the values of LjSCVW noticeably increased. Three types of data-driven models (DDMs), namely, support vector regression (SVR), gene expression programming (GEP), and a robust hybrid model entitled hybrid (SVR-ACO) are developed to estimate the LjSCVW. The suggested hybrid model is a coupled form of SVR with ant colony optimization (ACO) algorithm, which is used to enhance the estimation precision of the LjSCVW. According to the attained statistical indices (determination coefficient (R2) = 0.98, root mean square error (RMSE) = 0.191, and value of total grade (TG) = 19.78) and scatter plots, the hybrid SVR-ACO model was determined as the most superior method to estimate the LjSCVW with high accuracy. [ABSTRACT FROM AUTHOR]

A major challenge of prototype air-water flow measurement is the limited endurance of fragile phase-detection needle sensors in a high-momentum flow with risks of debris damage and particulate erosion. In the present study, a thick-tip conductivity probe is manufactured with sturdier needle sensors than the commonly used laboratory-sized probes. The large sensor tip had low chance to pierce small air bubbles and water droplets, leading to deterioration in the signal output quality, which prevents derivation of basic air-water flow properties using the conventional signal processing technique. To extract valid phase information from the low-quality signal, calibration experiments were conducted in laboratory with reference to a regular-sized probe, to explore a proper signal processing method for the thick-tip probe. The method was validated, and the thick-tip probe was deployed in a field hydraulic jump measurement, allowing for access to the air-water flow characteristics of the prototype D-type jump with a Reynolds number of 1.88×106. Despite the effort of signal calibration and compensation, the use of the thick-tip probe does not guarantee accurate bubble size measurement and requires higher sampling frequencies. Therefore, probes with fine sensor tips are still preferable in prototype measurement. [ABSTRACT FROM AUTHOR]

Flip buckets are commonly used to discharge flow from a hydraulic structure to the downstream as ski jump when flow velocity is large. Deflectors can be used to increase the efficiency of energy dissipation by flip buckets. This wedge-shaped structure deflects a portion of the flow by splitting it on the bucket. In this study, the effect of triangular deflectors which are used continuously across the channel, on energy dissipation by a flip bucket was experimentally investigated. For this purpose, a triangular deflector with three side lengths (3, 6 and 9 cm) and seven angles equal to 12°,17°, 22°, 27°, 32°, 37° and 42° was tested under different hydraulic conditions and the results were compared with a flip bucket without a deflector. The experiments were carried out in a laboratory flume with a length of 15 m, a width of 0.3 m and a height of 0.5 m. The results indicate that the model with a deflector increased energy dissipation by 8.2 to 22.7 percent as compared to that without a deflector. Increasing the deflector angle and side length initially increased energy dissipation, but then decreased it at large angles and lengths. An optimum angle of 27° to 32° was obtained with an optimal deflector length (L) to the Reynolds number (R) ratio of 0.46. A correlation was proposed to predict energy dissipation by the flip bucket with a triangular deflector using multivariate nonlinear regression. [ABSTRACT FROM AUTHOR]

In this paper, two artificial intelligence (AI) techniques, including Deep Learning (DL) and Multi-Layer Perceptron (MLP), have been applied to predict the pressure fluctuations coefficient (CʹP) along the submerged and free jumps at the bottom of the USBR Type II stilling basin, based on the geometric and hydraulic parameters. This coefficient is significant for evaluating the uplift and cavitation phenomena within the stilling basins. The measurements were conducted in a laboratory flume using the pressure transducers and the data acquisition system. The maximum values of CʹP occurred at the beginning of the stilling basin. The DL algorithm contains three hidden layers using (100,100,100) hidden neurons. The optimal structure for the MLP model was found to be 5–10‒1. In the testing set, using the DL model, the values of determination coefficient (R2), root mean square error (RMSE), mean absolute error (MAE), and Legate and McCabe's Index (LMI) were obtained 0.915, 0.003, 0.002, and 0.743, respectively. For the MLP model, the same values were obtained 0.522, 0.009, 0.007, and 0.199, respectively. It was verified that the DL model gives more accurate results for the CʹP coefficient. [ABSTRACT FROM AUTHOR]

Hydraulic model study was conducted on the 1:60 scale using 2-D model for mitigating local scour downstream of ski-jump bucket type energy dissipater under supercritical flow conditions with initial Froude number, Fr1 from 5.50 to 6.29 for all gates vented condition. The objective of this research was to assess and quantify the scour in downstream side of channel and select the most appropriate existing formulas for predicting maximum scour depth of a local scour hole. The relative scour depth for the experimental data is compared with different empirical equations. Among these equations, a good estimate of the measured scour depth is obtained for the Novak and Indian standard equation. The developed statistical equations to predict scour depth give a good agreement with the experimental data. Each scour depth formula has limitations, therefore does not perform well with different discharges for different gate operative conditions. For depth of scour computation, the Novak method is found to provide high accurate results with Nash-Sutcliffe efficiency (NSE) of 0.91, root-mean-square error (RMSE) of 4.66 m and mean absolute percentage error (MAPE) of 15%. However, in a data-constraint situation, the development of a new formula for scour depths computation will be more feasible. [ABSTRACT FROM AUTHOR]

Hydraulic jump that frequently occurs downstream of hydraulic structures reduces the excess energy of the incoming flow. This study tested two different heights of discontinuous roughness elements over the horizontal bed and two adverse slopes of -1.5% and -2.5% in the stilling basin. In total, 280 data were collected in laboratory conditions to assess the impact of adverse bed slope with a variation of roughness elements height on hydraulic jump characteristics, with Froude numbers ranging from 4.9 to 12.4. The results showed that the average value of the bed shear coefficient on the adverse slope of -2.5% with relative roughness elements of h/d1 = 1.33 was 12.4 times that in a smooth bed. The observation showed that the bed shear stress caused by the bed roughness reduced the sequent depth ratio and consequently increased the energy dissipation by generating large eddies and more turbulence. The reduction was more prominent when roughness elements and adverse bed slope height increased. On the other side, a semi-theoretical solution was presented based upon momentum analysis to assess the sequent depth ratio by considering upstream Froude number, roughness element height, and bed slope. The computed values were compared with the experimental measurements. Empirical predictive relationships were proposed to estimate hydraulic jump characteristics over adverse-sloped and rough beds. [ABSTRACT FROM AUTHOR]

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In this study, the FLOW 3D computational fluid dynamics (CFD) software was used to estimate the performance of the United States Bureau of Reclamation (USBR) type II and USBR type III stilling basins as energy dissipation options for the Mirani Dam spillway, Pakistan. The 3D Reynolds-averaged Navier–Stokes equations were solved, which included sub-grid models for air entrainment, density evaluation, and drift–flux, to capture free-surface flow over the spillway. Five models were considered in this research. The first model has a USBR type II stilling basin with a length of 39.5 m. The second model has a USBR type II stilling basin with a length of 44.2 m. The 3rd and 4th models have a USBR type II stilling basin with a length of 48.8 m and a 39.5 m USBR type III stilling basin, respectively. The fifth model is identical to the fourth, but the friction and chute block heights have been increased by 0.3 m. To set up the best FLOW 3D model conditions, mesh sensitivity analysis was performed, which yielded a minimum error at a mesh size of 0.9 m. Three sets of boundary conditions were tested and the set that gave the minimum error was employed. Numerical validation was done by comparing the physical model energy dissipation of USBR type II (L = 48.8 m), USBR type III (L =35.5 m), and USBR type III with 0.3-m increments in blocks (L = 35.5 m). The statistical analysis gave an average error of 2.5% and a RMSE (root mean square error) index of less than 3%. Based on hydraulics and economic analysis, the 4th model was found to be an optimized energy dissipator. The maximum difference between the physical and numerical models in terms of percentage energy absorbed was found to be less than 5%. [ABSTRACT FROM AUTHOR]

The present work studies the hydro-gasdynamic analogy between a shock wave, occurring in supersonic internal or external compressible flows, and a hydraulic jump, a sort of normal shock occurring in open-channel flows. It consists of an extensive theoretical framework followed by a practical analysis, the aim of which was to experimentally trigger the hydraulic jump, both normal and oblique, while using a low-cost designed lab prototype. The assembly development, called 'water table', arises from the necessity of economical alternatives to expensive supersonic wind tunnels in the experimental study of compressible fluid dynamics. With this objective in mind, a hydraulic canal based on a Laval nozzle was constructed where water flow could accelerate from subcritical to critical to supercritical regime and then return to subcritical regime through a hydraulic jump. In addition, multiple design alternatives were evaluated considering environmental, economic, functional and aesthetics factors. A low-cost implementation was the critical criterion in the design process. The measurements have revealed that the geometry of the nozzle and the wedges designed as obstacles to cause obliquity are the most significant and influential elements in the formation of a hydraulic jump in the experimental set-up. Regarding the experimental variables, the experiments demonstrate the effect of the upstream and downstream heights of the hydraulic jump in the data collection. This experience is a step forward in supporting students in the understanding of compressible flow and its principles by providing an in-house experimental set-up that promotes active learning, motivation and interest in fluid mechanics. [ABSTRACT FROM AUTHOR]

Flow field characterization in high-aerated flows often involves flow imaging techniques through transparent sidewalls, and the results may be subject to sidewall effects and thus differ from the central flow behaviors. This paper contributes an experimental investigation of the sidewall effects on the air-water flow distributions in quasi-two-dimensional hydraulic jumps in a rectangular flume. The tested hydraulic jumps are characterized by preaerated approach flows and large inflow Froude numbers from 10.6 to 15.1. The air-water flow properties are measured intrusively along the centerline, sidewall, and transverse cross sections to provide a three-dimensional view of the aerated flow structure. Substantial redistribution of the bubbly flow is observed due to the presence of lateral aeration boundary layers in the high-speed jet-shear region, compared to the less affected free-surface roller. The magnitude difference between the central and lateral air-water flow properties is more distinct in terms of bubble count rate and less evident for void fraction and interfacial velocity, while the affected area is broader for void fraction distributions. The results suggest a concentration of high-speed jet flow in the central bottom flow column, where the jet layer is thicker, the recirculation roller is smaller, and the proportion of small-size bubbles is higher. The width of the central flow region free of the sidewall effects is approximately 60% to 80% of the flume width in the present facility, narrower on the bottom, and broader at the free surface. The findings demonstrate that the transverse variation of air-water flow and the difference between the central and lateral flow fields should not be ignored for the high-speed flow regions of hydraulic jump. A correct assessment of the sidewall effects is essential for interpreting imaging-based measurement of highly-aerated flow. [ABSTRACT FROM AUTHOR]

An exact solution to the lock-exchange problem, which is a two-layer analogue of the classical dam-break problem, is obtained in the shallow-water (SW) approximation for two immiscible fluids with slightly different densities. The problem is solved by the method of characteristics using analytic expressions for the Riemann invariants. The obtained solution, which represents an inviscid approximation to the high-Reynolds-number limit, is, in general, discontinuous containing up to three hydraulic jumps which are due to either multivaluedness or instability of the continuous SW solution. Hydraulic jumps are resolved by applying the Rankine–Hugoniot conditions for the SW mass and generalized momentum conservation equations. The latter contains a free parameter α which defines the relative contribution of each layer to the interfacial pressure gradient. We consider a solution for α = 0 , which corresponds to both layers affecting the interfacial pressure gradient with equal weight coefficients. This solution is compared with the solutions resulting from the application of the classical Benjamin's front condition as well as the circulation conservation condition, which correspond to α = − 1 and α → ∞ , respectively. The SW solution reproduces all principal features of 2D numerical solution for viscous fluids. The gravity current speed is found to agree well with experimental and numerical results when the front acquires the largest stable height which occurs at α = 5 − 2. We show that two-layer SW equations for the mass and generalized momentum conservation can describe interfacial waves containing hydraulic jumps in a self-contained way without external closure conditions. [ABSTRACT FROM AUTHOR]

This study explores the physics of laminar planar hydraulic jump of power-law liquids in a horizontal channel through shallow water analysis. The theory is supplemented and validated by numerical simulation performed by the phase-field method in COMSOL Multiphysics. The analysis is applicable for shear thinning as well as thickening liquids and reduces to Newtonian equations when the flow behavior index (n) is unity. The analytical and numerical results are further validated with experimental data of the present study. The steady state free surface profile in conjunction with a modified Bélanger type equation predicts jump location and strength (the ratio of film height just after and before the jump). The analysis provides a modified scaled relationship between the jump location and the liquid flow rate compared to that proposed for inviscid and viscous Newtonian liquids. An order of magnitude analysis expresses the scaled jump location and strength as a function of inlet Reynolds number (Rein), inlet Froude number (Frin), scaled channel length, and n. We find that an increase in the flow consistency index and/or n favors jump formation and the jump shifts toward the channel exit with increasing n for the same channel geometry, Rein and Frin. The influence of scaled channel length is more pronounced for n < 1 as compared to n > 1 while shear thickening liquids are more significantly influenced by Frin at fixed Rein and scaled channel length. The coupled effect of flow parameters on jump characteristics is depicted in the Rein–Frin plane, which denote the range of the existence of different jump types as the function of n. [ABSTRACT FROM AUTHOR]

Air–water mixing associated with high turbulence is a common hydraulic phenomenon, where the transport of entrained air bubbles and the dissipation of turbulent energy are key processes affecting the air–water mass transfer. Herein hydraulic jumps were selected as a seminal case of self-air-entrainment in transitional water flow, and the air–water flow properties were investigated at high Froude numbers from 10.5 to 13.5. The analysis of air concentration distributions and bubble size spectra enabled deviation of the rates of bubble diffusion and turbulence dissipation. The study was facilitated with re-analyses of earlier experimental data for smaller Froude numbers between 3.8 and 10. The spatial evolution of the diffusion and dissipation rates suggested that the diffusion of air bubbles and dissipation of turbulent structures were not independent processes, and, at high Froude numbers, the mix of air and water was subject to re-aeration of the turbulent shear layer by the roller. [ABSTRACT FROM AUTHOR]

Reaeration is a primary path of reoxygenation in streams, fundamental to environmental and ecological integrity. Previous laboratory studies of reaeration rates in subcritical flows showed large scatter in results, with differences in mass transfer coefficients of more than one order of magnitude between comparable flow conditions. Although supercritical flow is commonly observed in natural streams and engineered channels, systematic measurements of supercritical flow reaeration rates have been unavailable. Experiments in a laboratory open channel flume encompassing sub- and supercritical flows have been undertaken. The subcritical data were consistent with a large body of previous studies. Supercritical flows showed 6–10 times stronger reaeration rates than comparable subcritical conditions, while local rates at hydraulic jumps systematically exceed those in the supercritical flows upstream by a factor up to three. A close relationship between reaeration rates and turbulent dissipation rate is observed, and a systematic Froude number dependency is demonstrated for both sub- and supercritical flows. Observed mass transfer coefficients do not correlate as well with flow Reynolds number and shear Reynolds number. The higher reaeration rates associated with supercritical flows indicates that a change in open channel flow regime for the same Reynolds number may be used to improve water quality. [ABSTRACT FROM AUTHOR]

Scour downstream of smooth and rough rigid aprons under wall jets has been studied experimentally. Effect of apron roughness on scour has been investigated, and quantification of reduction in the scour depth due to rough apron has been performed. Characteristics of velocity and turbulence over smooth and rough aprons as well as within the scour hole have been analyzed to study the behavior of the jet and its interaction with the rough apron. Results show that there is a significant reduction in the equilibrium scour depth due to roughness. A maximum of 82.8% and a minimum of 31.1% reduction in the equilibrium scour depth was observed due to inducing roughness over the rigid apron. Velocity characteristics establish the cause of reduction in the equilibrium scour depth, which is due to reduction in the erosive capacity of the jet as it moves over the rough apron. The potential core of the jet gets consumed at a much lesser length due to roughness over the apron than over a smooth apron, as the boundary layer develops at a smaller distance. Further, it was observed that it takes a smaller length for the flow to get fully developed under the rough apron as compared with the smooth apron. Based on the results of the present analysis, recommendation can be made for use of roughness over the apron to restrict scour due to wall jets. [ABSTRACT FROM AUTHOR]

The current research investigates experimentally the flow passing through combined hydraulic structure consists of V-notch sharp crested weir and inverted V-shaped sharp gate installed in straight channel as a control structure. Nine structure models were used considering three different vertex angles simultaneously used for the weir and the gate (θ = 60°, 90° and 120°). Eighty-one experimental runs were executed to explore the influence of the combined structure geometry, the upstream head, and the tailwater depth on the conveyed flow, the discharge coefficient and the downstream flow pattern with special emphasize on the hydraulic jump characteristics. The outcomes were analyzed and graphically presented. The results proved that the simultaneous flow through the combined structure regardless the vertex angles conveyed more discharge with less downstream water disturbance on account the classical V-notch weir and the inverted V-shaped gate. The flow discharge increased up to 10 times, and the discharge coefficient increased by around 26% for combined structure of 120° vertex angle under similar hydraulic conditions. The conveyed discharge was influenced by the gate angle than the weir angle. The downstream flow characteristics were more sensitive to the weir angle than the gate angle under similar hydraulic conditions. The measured hydraulic jump lengths were compared to other formulas and showed good agreement. Also, the weir and gate vertex angles effectively influenced the hydraulic jump characteristics. The outcomes were used to develop empirical equations for predicting the discharge coefficient and dimensionless jump length associated to the combined structure. The results and analysis in this research are limited to tested data range. [ABSTRACT FROM AUTHOR]

This paper presents a 0.25-scale quasi-three-dimensional hydraulic model experiment of transient fluid flow phenomena during continuous casting of steel under solidification. Water cooling is performed at the bottom of the mold, and saturated sodium acetate solution is covered on the spring and particle arrangement at the bottom of the mold/on the dummy bar to simulate the solidification phenomenon in the actual continuous casting process. The results show that the solidification on the dummy bar surface is very important to the early stage of the filling process and cannot be ignored. Its influence gradually decreases with the rise of the liquid level, and basically disappears when the liquid level rises to a certain height (steady liquid level, SLL). In SLL, the interface morphology of the solidified layer is more affected by the flow, while the interface morphology of the solidified layer has no significant effect on the liquid surface velocity. [ABSTRACT FROM AUTHOR]

The Split wildfire in July 2017, which was one of the most severe wildfires in the history of this Croatian World Heritage Site, is the focus in this study. The Split fire is a good example of a wildfire–urban interface, with unexpected fire behavior including rapid downslope spread to the coastal populated area. This study clarifies the meteorological conditions behind the fire event, those that have limited the effectiveness of firefighting operations, and the rapid escalation and expansion of the fire zones within 30 h. The Split fire propagation was first reconstructed using radio logs, interviews with firefighters and pilots involved in the intervention, eyewitness statements, digital photographs from fire detection cameras, media, and the monthly firefighting journal. Four phases of fire development have been identified. Then, weather observations and numerical simulations using an enhanced-resolution operational model are utilized to analyze the dynamics in each phase of the fire runs. The synoptic background of the event includes large surface pressure gradient between the Azores anticyclone accompanied by a cold front and a cyclone over the southeastern Balkan Peninsula. At the upper level, there was a deep shortwave trough extending from the Baltic Sea to the Adriatic Sea, which developed into a cut-off low. Such synoptic conditions have resulted in the maximum fire weather index in 2017. Combined with topography, they also locally provoke the formation of the strong northeasterly bura wind along the Adriatic coast, which has been accompanied by a low-level jet (LLJ). The bura (downslope wind), with mid- to low-level gravity-wave breaking and turbulence mixing (as in the hydraulic jump theory), also facilitated the subsidence of dry air from the upper troposphere and rapid drying at the surface. This study demonstrates that numerical guidance that indicates the spatial and temporal occurrence of a LLJ is highly capable of explaining the Split fire evolution from the ignition potential to its extinguishment stage. Thus, in addition to the conventional fire weather indices, such products are able to improve fire weather behavior forecasting and in general more effective decision-making in fire management. [ABSTRACT FROM AUTHOR]

The effect of fluctuating pressures due to turbulence on the hydraulic jump causes significant damage to the relaxation pool. Moreover, the presence of roughness in the bed changes the behavior of flow lines and the formation of vortices during the jump. Therefore, the aim of this study was to determine the effect of the presence of roughness on hydrodynamic pressures in type S hydraulic jump in sudden divergence sections. For this purpose, experiments were performed in a relatively large channel with a width of 0.8 and a length of 12 m in the calm pool with divergence ratios of 0.33, 0.5, 0.67 and 1 in the range of Frued numbers between 2 to 9.5. Roughness elements with a height of 3 cm and specified distances were placed in the channel bed and downstream of the divergence section. In order to determine the effects of roughness on the level of hydrodynamic pressures, the experiments were performed in two separate stages, including a completely flat pool bed without the presence of roughness in the first stage (77 experiments) and with the presence of roughness in the pool floor in the second stage (81 experiments). The results showed that the presence of roughness in the bed reduces the intensity of pressure fluctuations in the relaxation pool. In addition, in sudden divergent sections, due to the formation of lateral vortices, the energy drop increases and the intensity of pressure fluctuations decreases. The maximum reduction rates of pressure fluctuations were estimated to be 27, 46 and 58% for the divergence ratios of 0.67, 0.5 and 0.33 in the rough bed, respectively.

In this study accuracy of the ANFIS and ANFIS-PSO models to estimate hydraulic jump characteristics including sequence depth ratio, the jump length, the roller length ratio, and relative energy loss was evaluated in stilling basin versus laboratory results. The mentioned characteristics were measured in the stilling basin with a rectangular cross-section with four different adverse slopes, four diameters of bed roughness, four heights of positive step, three Froude numbers, and four discharges. The average statistical parameters of NRMSE, CRM, and R2 for estimating hydraulic jump characteristics with the ANFIS model were 0.059, -0.001, and 0.989, respectively. While, the mean values of these parameters for the ANFIS-PSO model were 0.185, 0.002, and 0.957, respectively. The results indicated that these models were capable of estimating hydraulic jump parameters with high accuracy. However, the ANFIS model was moderately more accurate than the ANFIS-PSO model to estimate the sequence depth ratio, the jump length, the roller length ratio, and relative energy loss.

The movements of fishes in natural river systems are affected by in-stream man-made structures, including dams and weirs. The effect of downstream fish passage over dam spillways has received little attention to date. In 2010, some observations of downstream fish passage were conducted at the Paradise Dam spillway, Australia during two markedly different flood events. The spillway was equipped with an un-gated crest, a steep stepped chute and a hydraulic jump energy dissipator without baffle block. The data on downstream fish passage at Paradise Dam are herein re-analysed with a focus on downstream fish passage over the spillway and associated mortality, together with some complementary information on the spillway operation. The mortality rates of fish passing on the Paradise Dam stepped spillway were very low. Under skimming flow conditions, the relative mortality rate was 0.085% of fish passing over the spillway on 3–4 March 2010. A higher mortality rate was seen under nappe flow conditions, although comparable to smooth chute fish mortality data. In average, the fish mortality data downstream of the Paradise Dam spillway was between 7 and 27 times lower than the natural fish mortality in the reservoir. Overall, the present data analyses demonstrated un-equivocally the significance of the spillway flow regime on the downstream fish passage mortality rate. It showed the adverse impact on fish during downstream passage at very-low flows, i.e. q < 0.01–0.02 m2.s−1, with both smooth-invert and stepped invert spillways. The finding highlighted a need for efficient downstream fish-friendly passage designs, adapted to the relevant spillway designs, and a number of low-flow fish-friendly channel designs are discussed. [ABSTRACT FROM AUTHOR]

This study investigates the effects of gate openings and different sill widths on the sluice gate’s energy dissipation and discharge coefficient (Cd). The physical model of the sills includes rectangular sills of different dimensions. The results show that the gate opening size is inversely related to the Cd for a gate without a sill. In addition, increasing the gate opening size for a given discharge decreases the relative energy dissipation, and increasing the Froude number increases the relative energy dissipation. The results also show that the Cd and relative energy dissipation decrease when the width of the sill is decreased, thus increasing the total area of the flux flowing through the sluice gate and vice versa. According to the experimental results, the relative energy dissipation and the Cd of the sluice gate are larger for all sill widths than without the sill. Finally, non-linear polynomial relationships are presented based on dimensionless parameters for predicting the relative energy dissipation and outflow coefficient.

Gravity water delivery systems are common around the world to transport water without the use of external energy. The systems’ inadequate design and operation tend to form entrapped air bodies in downward pipeline lengths. Entrapped air generates considerable energy losses when there are no air admission-expulsion valves or due to valve failures. Air removal by hydraulic means has been modeled under various pipeline diameters, downward slopes, and air volume conditions. However, no generic entrapped air removal models exist, and the study in small diameters (≤50 mm) is limited. Most of the models reported in the literature were obtained for diameters greater than 50 mm, presenting notorious discrepancies among each other. In this research, the entrapped air removal in small diameter pipelines was studied (12.7, 15.875, 19.05, 25.4, 31.75, and 38.1 mm), highlighting the importance of the joint study of the air bubbles’ removal by the turbulent action of a hydraulic jump downstream of an air body and the consequent removal of remaining entrapped air by a hydrodynamic thrust. Potential models were found for the air bubbles’ removal for different pipeline diameters and downward slopes. Linear relationships were found between the dimensionless air removal parameter and the pipeline’s downward slope.

Hydraulic jump is a highly important phenomenon for dissipation of energy. This event, which involves flow regime change, can occur in many different types of stilling basins. In this study, hydraulic jump characteristics such as relative jump length and sequent depth ratio occurring in a suddenly expanding stilling basin were estimated using hybrid extreme learning machine (ELM). To hybridize ELM, imperialist competitive algorithm (ICA), firefly algorithm (FA) and particle swarm optimization (PSO) metaheuristic algorithms were implemented. In addition, six different models were established to determine effective dimensionless (relative) input variables. A new data set was constructed by adding the data obtained from the experimental study in the present research to the data obtained from the literature. The performance of each model was evaluated using k-fold cross-validation. Results showed that ICA hybridization slightly outperformed FA and PSO methods. Considering relative input parameters, Froude number (Fr), expansion ratio (B) and relative sill height (S), effective input combinations were Fr–B–S and Fr–B for the prediction of the sequent depth ratio (Y) and relative hydraulic jump length (Lj/h1), respectively. HIGHLIGHTS Suddenly expanding stilling basins were examined both experimentally and using AI.; Hydraulic jump characteristics were estimated using hybrid extreme learning machine.; New laboratory data was modeled using novel machine learning algorithms.; Among optimization algorithms, ICA was superior to PSO and FA.; The performance of each model was evaluated using k-fold cross-validation.;

The transient flow of a circular liquid jet impinging on a horizontal disk, and the hydraulic jump formation, are examined theoretically and numerically. The interplay between inertia and gravity is particularly emphasised. The flow is governed by the thin-film equations, which are solved along with a force balance across the jump. The unsteadiness of the flow is caused by a linearly accelerating jet from an initial to a final steady state. To validate the predicted boundary-layer flow evolution, an analytical development is conducted for small distance from impingement, and for small time. In addition, the predictions of the film profile and jump location are compared against numerical simulation for the transient flow, and are further validated against experiment for steady flow. The evolutions of the film thickness and the wall shear stress in the developing boundary-layer region are found to be similar to those reported for a fluid lying on a stretching surface. The flow responds to the jet acceleration quasi-steadily near impingement but exhibits a long-term transient behaviour near the jump. Analysis of the jump evolution is considered in the range 5 < Fr < 40 for the Froude number (based on the jet radius and velocity). For Fr < 10, the jump reaches the final state instantly when the jet acceleration ceases. At higher Froude number, the jump settles at a later time, exhibiting an overshoot in the thickness due to the dominance of inertia. [ABSTRACT FROM AUTHOR]

Pressure fluctuations are a critical phenomenon that can endanger the safety and stability of hydraulic structures, especially stilling basins. Hence, the accurate estimation of the dimensionless coefficient of pressure fluctuations (C P ′) is critical for hydraulic engineers. This study proposed predictive soft computing models to estimate C P ′ on sloping channels. Therefore, three robust soft computing methods, including extreme learning machine (ELM), group method data of handling (GMDH), and M5 model tree (M5MT), were used to estimate C P ′. The results revealed that ELM was more accurate than GMDH and M5MT methods when comparing statistical indices, including correlation coefficient (CC), root mean square error (RMSE), mean absolute error (MAE), scatter index (SI), index agreement ( I a ), and BIAS values. The performance of ELM was found to be more accurate (CC = 0.9183, RMSE = 0.0067, MAE = 0.0051, SI = 11.88%, Ia = 0.9569) when compared with the results of GMDH (CC = 0.8818, RMSE = 0.0078, MAE = 0.0058, SI = 13.89%, Ia = 0.9361) and M5MT (CC = 0.6883, RMSE = 0.0120, MAE = 0.0090, SI = 21.28%, Ia = 0.7905) in the testing stage. In addition, the BIAS values revealed that ELM slightly overestimated the values of C P ′ , especially at the peak point compared with GMDH and M5MT results. Overall, the suggested soft computing techniques worked well for predicting pressure fluctuation changes in the hydraulic jump. [ABSTRACT FROM AUTHOR]

We examine theoretically the structure of the non-circular jump for an impacting circular jet, induced by azimuthally dependent edge conditions. We show that the supercritical flow remains axisymmetric for a thin film. The subcritical flow is assumed to be inertialess. The loss of axial symmetry is induced by disk non-circularity or periodic edge film thickness. The jump is treated as a shock, where the balance of mass and momentum is established in the radial and azimuthal directions, including the non-axisymmetric effect of surface tension across the jump. The geometry of a non-circular disk has little influence on the shape of the jump, except when the jump occurs close to the disk edge, but the subcritical flow field can be highly non-axisymmetric even for a circular jump. For a jet impinging on a circular disk with a variable film thickness at the edge, we find that a small azimuthal variation in the edge thickness leads to a significant loss of axial symmetry. The nonlinearities in the balance equations across the jump cause an increase in the number of peaks and valleys as the disk radius decreases. Flow reversal occurs in the polar plane at alternating valleys. It is important to mention that this is a study in (edge) controlled pattern generation and therefore not aimed at simulating or interpreting the spontaneous non-circular jumps reported in the literature. [ABSTRACT FROM AUTHOR]

The study looks at the possibility of reducing the length of a rectangular hydraulic jump stilling basin by setting up a broad-crested sill. The conclusions of the study are based exclusively on laboratory tests using a specially designed hydraulic installation. The sills tested meet the hydraulic and geometric conditions of broad-crested sills suggested by the literature, in particular the Rao and Muralidhar study of 1963. The dimensionless parameters involved in the problem are the relative sill height S = s/h1, the relative length of the stilling basin X/h1 corresponding also to the relative position of the sill, and the Froude number F1 of the incident flow of depth h1. However, experimentation shows that the relative length X/h1 of the basin depends only on one of the parameters S or F1. An explicit experimental relationship between the three parameters involved X/h1, S and F1 is derived, bearing in mind that S and F1 are related by a theoretical relationship according to a previous study conducted by the authors. The experimental tests involve the following wide ranges: 1 ≤ S ≤ 6.15, 18 ≤ X/h1 ≤ 60, and 3.082 ≤ F1 ≤ 9.20, which allow drawing quality conclusions. The compactness of the stilling basin is evaluated by the ratio X/Lj*, where Lj* is the length of the classical hydraulic jump evolving freely on a horizontal apron without a sill. The sequent depth ratio Y* = h2*/h1 of this type of hydraulic jump is related to the incident Froude number F1 by the well-known Belanger's theoretical relationship successfully demonstrated in 1828, which remains unchanged. Using the obtained appropriate experimental dimensionless relationship, combined with the Bradley and Peterka experimental equation giving the length of the classic hydraulic jump, it is shown that the ratio X/Lj* is always less than unity regardless of the value of the Froude number F1. This fact clearly indicates that the setup of a broad-crested sill has a reducing effect on the length X of the stilling basin. An in-depth study of the variation curve of X/Lj* against F1 reveals that the best compactness is obtained for F1 = 7.311, giving X/Lj* ≈ 0.765, which corresponds to a compactness rate of 23.5%. [ABSTRACT FROM AUTHOR]

The paper discloses the study of flow crisis in the Ranque—Hilsch vortex tube with a square channel. Previous studies have found the conditions for developing the hydraulic crisis for air flow in this type of tube. The crisis phenomenon is related to the event when the longitudinal velocity at the nearwall vortex-circulation zone interface approaches the value of velocity for spreading centrifugal waves along this boundary. The paper presents and discusses the new detailed results in measuring the kinematic parameters of the crisis flow, including the parameter of velocity pulsation. The evidence of a hydraulic jump near the exit of the swirl flow to the tube working channel. [ABSTRACT FROM AUTHOR]

Flowing lava and water have dramatically different physical properties but can form similar hydraulic structures, including undular hydraulic jumps, or standing wave trains. In water flows, undular hydraulic jumps are evidence of critical flow (Froude number ∼1) and open‐channel hydraulic theory provides a powerful tool for estimating flow depth and velocity. Monitoring these parameters in an active lava channel is inherently challenging, but essential for calculating lava discharge (effusion rate), a primary control on the rate of flow front advance and ultimate flow runout distance. We analyze undular hydraulic jumps in both water and lava flows to assess the conditions under which they form and, by extension, the potential use of critical flow theory to estimate, in real time, lava flow velocity, depth, and discharge. Experimental data for water flows show that these structures mark the transition from supercritical to subcritical flow. Undular hydraulic jumps in the near‐vent lava channel of the 2018 lower East Rift Zone eruption of Kīlauea, Hawaiʻi also reflect critical flow conditions; their wavelengths scale with flow depth and velocity, consistent with hydraulic theory. Calculated lava effusion rates are similar to estimates made using more traditional approaches (Jeffreys', 1925, https://doi.org/10.1080/14786442508634662, equation based on lava viscosity, density, and channel slope) and with lava volumes derived from topographic‐change mapping. From this we conclude that critical flow phenomena show great potential to track flow dynamics and inform hazard assessment for a wide range of geophysical fluids. Plain Language Summary: Flowing water and lava have very different physical properties, but under certain flow conditions, each will form arrays of evenly spaced standing waves (wave trains). In water, these are known to form at "critical flow" when there is a specific ratio between flow depth and flow velocity. However, conditions for forming standing wave trains in lava have not been measured. We investigated the relationship between the spacing of waves in a train, and the flow speed and depth, using both data from experiments with water and measurements made during the 2018 lava flow at Kīlauea volcano. We found that waves form in each fluid at the same ratio of flow speed and depth, and that the spacing of waves in a train shows a fixed mathematical relationship to these parameters. There is considerable practical importance to this finding. During a volcanic eruption, direct measurement of flow speed is difficult and dangerous, and depth is impossible, and yet both are needed to predict how far and how fast lava will travel. The critical flow characteristics of lava, and potentially other hazardous flows such as mudflows, allow assessment of flow behavior and potential hazards in real time. Key Points: Undular hydraulic jumps, or standing wave trains, form in both water and active lava at critical flow (Froude number ∼1)Wavelengths scale with flow depth and velocity following hydraulic theory in water flume experiments and Hawaiian lava flow dataApplication to wave trains in active lava flows provides rapid estimates of key flow parameters and effusion rates for hazard assessment [ABSTRACT FROM AUTHOR]

Since the hydraulic jump off a tidal bore in the Kampar Estuary has never been well-described, real-time measurements of hydraulic jump properties are crucial to understanding the tidal bore characteristics. This study aims to determine the real-time properties of a tidal bore generation, hydraulic jump, and transport mechanism in the Kampar River estuary. Tidal harmonic and range are analyzed using least-square-based tidal modeling. The tidal bore height and turbulent velocity records based on ADCP surveys in the estuary and upstream area are used to determine the hydraulic jump properties. Furthermore, an acoustic-based approach is also employed to quantify the suspended sediment concentration and flux during the passage of the bore. Kampar Estuary is predominated by semidiurnal co-tidal components (M2 and S2), where, based on the phase lag magnitude, it is categorized as an ebb-dominant estuary. This finding is proven by the more intense and prolonged ebb phases, especially during spring tidal conditions where the tidal range reaches 4 m. Of particular concern, the tidal bore height declines by 1.5 m every 20 km upstream with an erratic turbulent velocity. A sudden increase in transverse and vertical velocity during the passage of bore (ranging from −0.9 to 0.2 m/s) reflects the potency of sediment resuspension in the surrounding river edge marked by the significant increase in suspended sediment flux of about 3.7 times larger than at the end of the ebb tide. However, long-term measurement and regular bathymetry surveys are crucial to monitor the tidal bore behavior and morpho-dynamics in the Kampar River estuary. [ABSTRACT FROM AUTHOR]

Water flow often releases excess energy after passing through gates and spillways. This energy should be reduced to avoid the destruction of downstream structures. The hydraulic jump, a natural phenomenon, inevitably reduces incoming flow energy. The experiments were carried out in this study to investigate the effect of bed roughness and abrupt negative drops on the characteristics of the hydraulic jump. Also, to investigate the effect of geometric and hydraulic parameters on energy dissipation and location of the hydraulic jump, there was a change in the height of the abrupt drop and roughness for different discharges between 30 and 50 L/s and the Froude numbers were ranging from 4.9 to 9.5. The results showed that increasing the bed roughness causes a reduction of the sequent depth ratio and the relative length of the jump by 16.6% and 20.7%, respectively, and increases the relative energy loss and the bed shear force coefficient by 10% and 31%, respectively. In contrast, increasing the step height causes an increase in the sequent depth ratio and the relative length of the jump by 6.5% and 7%, respectively, and increases the relative energy loss and the bed shear force coefficient by 11% and 3.2%, respectively. [ABSTRACT FROM AUTHOR]

The multiple-barrier mitigation strategy in the debris-flow source area is an effective approach to inhibit debris-flow entrainment and scale amplification along the flow path. However, less is known as debris flow overflows a filled barrier and cascades downstream. The present study investigates the physical processes and load characteristics of debris-flow overflowing a model flexible barrier, using a well-instrumented medium-scale flume. Volumetric solid concentration is varied ranging from 0.4 to 0.6 so that the control factors (e.g., state of liquefaction and turbulent drag) in the overflow process can be identified. The results demonstrate that effective stress is not observed in the incoming debris flows for solid concentration up to 0.6, denoting a contribution of turbulent drag to the overflow drag. The formed hydraulic jump substantially elevates the overflow depth above the flexible barrier, which has not been considered in the current design guideline. Decomposition of the total overflow load reveals that the increase in total load is actually dominated by the static load due to the elevated flow depth, rather than the turbulent drag. Downward momentum transfer to the lower section of barrier is observed and re-liquefaction of the deposited debris is a prerequisite for the downward momentum transfer. Different from the high solid-concentration cases, the deposit of low solid concentration (0.4) behind the barrier is partially drained with nontrivial effective stress, which further hinders the downward momentum transfer to the base of the barrier. The findings of present study indicate that the debris-flow properties are the key control factors for the complicated debris-barrier interaction. [ABSTRACT FROM AUTHOR]

Under a flow in supercritical regime, depending on the pier width to water depth ratio, the flow pattern around a bridge pier can take the form of a wall-jet-like bow wave or a detached hydraulic jump. The present work aims at analysing the maximum scour depth at piers in both flow patterns. A dedicated experimental set-up was used to produce the live-bed scour experiments, varying the inflow velocity and pier diameter. During the experiments, scour developed very rapidly, achieving equilibrium conditions after few minutes. No major differences between the maximum scour depth in the wall-jet-like bow wave and detached hydraulic jump cases were observed. Measured scour depths were of comparable magnitude and followed similar tendencies with controlling parameters as in subcritical flows. Scour formulas for piers in subcritical flow thus achieve a good accuracy in prediction of maximum scour depth at piers in supercritical flows. [ABSTRACT FROM AUTHOR]

The principle theme of this study is to introduce a novel countermeasure to reduce the energy of the overflowing floodwater by utilization of a water cushion. For this purpose, laboratory experiments including "LW" cases (levee with water cushion) and "OL" cases (only levee) were conducted to elucidate the role of a water cushion in the flow structure variation after a levee is overflowed and to reduce energy. A moat (a deep and wide trench) with varying non-dimensional length (Lm* = Lm/hL; Lm is the length of the moat where hL is the levee height) and depth (Dm* = Dm/hL; Dm is the moat depth) acting as a water cushion was provided at the toe of a levee with varied landward slopes (SL). The energy reductions in the LW and OL systems were found to be very close to each other at lower overflow water depths, while it was 25% greater in the LW system than in the OL system at higher overflow water depths. Changes in the landward slope (SL) of the levee, non-dimensional length (Lm*), and depth (Dm*) of moat significantly changed the flow structure and created six different flow structures. However, 1–6%, 1–3%, and 1–5% differences in energy reduction rate were observed by varying SL, Lm*, and Dm*, respectively, in LW cases. All flow structures contributed greatly to energy reduction, but the energy reduction rate was maximum in flow structure named as T-2. Flow structures named as T-2 and T-6 are preferable due to increased water depth inside the moat and presence of submerged hydraulic jump which can be achieved during landward slopes SL = 1:1, 1:2 and by decreasing Lm* Dm*, of moat during Landward slope SL = 1:3. Article Highlights: The water cushion function of moat was utilized at toe of overflowing levee. The effect of different non-dimensional overflow water depths, non-dimensional length, depth of moat and varying landward slope of levee on flow structure was investigated. Different flow structure was classified based on non-dimensional length and depth of moat. Relation between flow structure and energy reduction rate was investigated. [ABSTRACT FROM AUTHOR]

Hydraulic jumps are commonly employed as energy dissipators to guarantee long-term operation of hydraulic structures. A comprehensive and in-depth understanding of their main features is therefore fundamental. In this context, the current study focused on hydraulic jumps with low Froude numbers, i.e. Fr1 = 2.1 and 2.4, at relatively high Reynolds number: Re ~2 × 105. Experimental tests employed a combination of dual-tip phase-detection probes and ultra-high-speed video camera to provide a comprehensive characterisation of the main air-water flow properties of the hydraulic jump, including surface flow features, void fraction, bubble count rate and interfacial velocities. The current research also focused on the transverse distributions of air-water flow properties, i.e. across the channel width, with the results revealing lower values of void fraction and bubble count rate next to the sidewalls compared to the channel centreline data. Such a spatial variability in the transverse direction questions whether data near the side walls may be truly representative of the behaviour in the bulk of the flow, raising the issue of sidewall effects in image-based techniques. Overall, these findings provide new information to both researchers and practitioners for a better understanding of the physical processes inside the hydraulic jump with low Froude numbers, leading to an optimised design of hydraulic structures. Article Highlights: Experimental investigation of air-water flow properties in hydraulic jumps with low Froude numbers Detailed description of the main air-water surface features on the breaking roller Transversal distribution of the air-water flow properties across the channel width and comparison between centreline and sidewall. [ABSTRACT FROM AUTHOR]

The use of a stilling basin with multiple horizontal submerged jets emerging from two layers has been suggested for use as an energy dissipation structure in hydropower stations. In this study, laboratory velocity measurement is performed to analyze the three-dimensional flow structure of submerged jets and to evaluate the effect of the downstream submergence on the flow field. The results indicate that the Reynolds shear stress and vorticity magnitudes increase with increasing jet submergence. Further, it was found that submergence increase leads to a decrease of 2.2% in maximum bed (floor) shear stress and 7.2% in side-walls shear stress. The Reynolds shear stress quadrant decomposition is also performed for all (H = 0) and high magnitude (H = 2) bursting events, which indicate that the turbulence events of outward and inward interactions made dominant contributions to the total Reynolds stress. Turbulent kinetic energy is also analysed to obtain a better characterization of the flow field. [ABSTRACT FROM AUTHOR]

On 19 April 2019, a mature squall-line mesoscale convective system (MCS) with the characteristics of a leading convective line and trailing stratiform landed on Taiwan, resulting in strong gust wind and heavy rainfall. This squall-line MCS became asymmetric after landfall on Taiwan. Two sets of idealized numerical simulations (mountain heights and low-level vertical wind shear) using the Weather Research and Forecasting (WRF) model were conducted to examine the impacts of realistic Taiwan topography on a squall-line MCS. Results showed numerous similarities between the idealized simulations and real-case observations. The low-level Froude number which considered the terrain height (Fmt) was calculated to examine the blocking effect of the Taiwan terrain, and the cold pool (determined by − 1.5 K isotherm) was found to be completely blocked by the 500-m height contour. The northeast-southwest orientation of the Snow Mountain Range (SMR), and the north–south orientation of the Central Mountain Range (CMR) led to the upwind side asymmetry. On the other hand, the lee-side asymmetry was associated with different intensities and occurrence locations of the hydraulic jump between the SMR and southern CMR, and the cold-pool Froude number (Fcp) indicated the flow-regime transition from subcritical to supercritical. [ABSTRACT FROM AUTHOR]

In this study, we examine the consistency of a gravity-based predictive theory for a hydraulic jump, given by Kurihara [Proceedings of the Report of the Research Institute for Fluid Engineering (Kyusyu Imperial University, 1946), Vol. 3, pp. 11–33]; Tani [J. Phys. Soc. Jpn. 4, 212–215 (1949)] with the phenomenological condition at the jump given by Rayleigh [Proc. R. Soc. London, Ser. A 90, 324–328 (1914)]; and Watson [J. Fluid Mech. 20, 481–499 (1964)] and show that in light of experimental evidence, the gravity-based predictive theory for the kitchen sink hydraulic jump is incompatible with the phenomenological condition, which must be valid. We also examine the solution to the downstream film and its potential influence on the hydraulic jump. We show that for all practical purposes, at normal flow conditions, the downstream liquid film remains flat and does not affect the jump, and the theory given by Bhagat et al. [J. Fluid Mech. 851, R5 (2018)] gives an excellent prediction of the jump radius. For high viscosity liquids, on a relatively large plate, the viscous dissipation in the downstream film could increase the jump height and, consequently, move the jump radius inward. [ABSTRACT FROM AUTHOR]

In the last decade, the use of gabion structures in hydraulic engineering for stabilizing the structure due to its high density and weight has become widespread. Also, the material's roughness and porosity cause it to be used in energy dissipation and drainage projects. This study evaluates the relative energy dissipation of gabion structures downstream of the ogee spillway in the conditions of a submerged hydraulic jump. The evaluated parameters in this study were Froude number, gabion height, gabion thickness, and material diameter. The experiments were performed with three average diameters of 1.5, 2.2, and 3 cm for rock material, three gabion heights of 10 and 20 cm, and Max. The end sill heights were 10, 20, and 30 cm. The operated discharges were regulated from 20 to 40 l/s. The results showed that by decreasing the average diameter of gabion aggregates, the amount of relative energy dissipation increases in all tested models, so that in gabion with a 1.5 cm average diameter of aggregates, the amount of energy dissipation increased by 3.6% in comparison with using the diameter of 3cm for the average diameter of the material. Increasing the height of the gabion to the extent that the flow is entirely inward can have up to 33% more relative energy dissipation than the gabion with a height of 10 cm. Also, by increasing the diameter of the gabion from 10 cm to 30 cm, relative energy dissipation increases up to 15%. [ABSTRACT FROM AUTHOR]

A hydraulic jump is a stationary transition from an upstream supercritical to a downstream subcritical flow. Hydraulic jumps with relatively low Froude numbers may be observed downstream of low-head hydraulic structures and their flow properties have not been not well documented. In this study, the hydraulic properties were investigated experimentally in weak hydraulic jumps with an inflow Froude number Fr1 = 2.1 and inflow depths 0.012 m < d1 < 0.130 m. Three novel features of the study were (1) the very wide range of inflow length scales tested systematically, (2) the relatively high Reynolds number Re = 3.05 × 105 achieved in the largest experiment, with the Reynolds number defined as Re = ρ × V1 × d1/μ, and (3) the broad range of inflow conditions. Although no air entrainment was observed at the lowest Reynolds numbers, some distinct air–water flow patterns were observed in the roller region, generally similar to those observed at higher Froude numbers. The ratio of downstream to upstream depths followed closely the analytical solution of the momentum principle irrespective of the inflow depth. On the other hand, noticeable scaling issues were observed in terms of the dimensionless roller length, length of air–water flow region, roller toe fluctuation frequency, and rate of air entrainment, with increasing dimensionless data with increasing inflow depths, hence Reynolds numbers. The present results have some practical implication in terms of physical modeling and upscaling of results for low-head hydraulic structures, including culverts and storm waterways, which typically operate with Reynolds numbers in excess of 105. [ABSTRACT FROM AUTHOR]

The hydraulic jump is a typical sudden change for mountain river areas. The effects of local hydraulic jumps on the particle transport capacity decrease and local flow resistance increase cannot be ignored as the sediment deposition disaster can amplify the flash flood disaster. The present research investigates the influences of a hydraulic jump on the individual particle movement and sediment deposition in a laboratory flume. The overall processes of a single particle movement are captured by a high-speed camera. The distribution of sediment deposition along the hydraulic jump is obtained statistically. The results show that both the particle size and the ratio of the upstream and downstream Froude numbers affect the particle motion process. A single particle coming from upstream gradually decelerates and finally stops at the hydraulic jump section because of hydraulic jump resistance. The particle acceleration first increases and then decreases during the time-domain process, and the attenuation trends are fast with the increase of ratio of upstream and downstream of Froude numbers. The increase of the maximum acceleration with sediment flows follows a linear trend approximately, which indicates that the kinetic features of the single sand particle are determined by the coupling effects of the hydraulic jump resistance and the sand dynamic properties. With the increase of sediment rate and sand particle size, the resistance effect of hydraulic jump on sediment deposition rate along the flow direction gets strong and the sediment deposition area is mainly located upstream of the hydraulic jump region. The present study shows that the possible sediment supply upstream must be obtained for identifying the disaster risk combined with the local hydraulic jump conditions. Further researches about the detailed critical condition deduced from the relationship between the water flow and sediment deposition are required to confirm and extrapolate present results to other applications. [ABSTRACT FROM AUTHOR]

This article presents a numerical technique that ensures the exact solution of stationary shockwaves, known as the hydraulic jump, for the one‐dimensional shallow water equations with the geometric source term. The mathematical description of the hydraulic jump is given by the Rankine–Hugoniot condition, at the interface of a control volume, where one variable in the system, the discharge, is supposed to be constant while the remaining variables are discontinuous. However, at the discrete level, the solution could be, for instance, a 3‐state jump, consisting of extra (intermediate) states resulting in the so‐called numerical anomaly. The anomaly is due to the nonlinearity of the Hugoniot locus and the fact that, at these points, a naive formulation is unlikely to avoid the inaccurate representation. The concept used here is simple, limit all discontinuous variables, that is, the surface flow data inside the cell that contains a shock with the data of the nearby cells where the shock is traveling to, allowing the solution to be linear. When used with a number of well‐known numerical solvers, namely Lax–Friedrichs, HLL, and Roe schemes, this approach is confirmed to accurately capture the moving and stationary shockwaves in the trans‐critical flow over nonflat beds. [ABSTRACT FROM AUTHOR]

The three-phase flow in a aeration tank driven by an inverted umbrella aerator is relatively complex, including the processes of the hydraulic jump, air entrainment, and sludge particle sedimentation. A three-phase flow test bench for an inverted umbrella aerator is established for studying its influence on aeration performance. The experiment mainly studies the changed law of aeration performance under different immersion depths or sludge concentrations and measures the flow rate and sludge concentrations in the aeration tank in different working conditions. The results are as follows. (1) The total oxygen transfer coefficient, standard oxygenation capacity, and standard power efficiency increase with the increase in rotational speed. The total oxygen transfer coefficient and standard-charge oxygen capacity first increase and then decrease with the decrease in immersion depth, reaching a maximum at −20 mm immersion depth. The standard dynamic efficiency has a similar trend and reaches a maximum at −8 mm immersion depth. (2) In the aeration tank, the flow velocity near the impeller is faster and has greater turbulence. The shallow water is more profoundly affected by the impeller compared with the deeper water. (3) The shallow-water sludge varies greatly, and the deep-water sludge is distributed uniformly when the inverted umbrella aerator works stably. [ABSTRACT FROM AUTHOR]