Search

The formation conditions of maximum- and minimum-wave jumps were experimentally investigated. A total of 110 wave-type jump experiments were carried out for several discharges, supercritical upstream and subcritical downstream water depths and drop heights. The experimental results revealed that the influential parameters on wave-type jumps are the upstream Froude number and the relative drop height. As the classical hydraulic jump equation is not sufficient to define conjugate depths of wave-type flow, empirical equations were developed for defining the conjugate depths of maximum-wave jumps and minimum-wave jumps (for which insufficient experimental data are available in the literature). The agreement between calculated and measured conjugate depths was good. It was also found that the value of the lower limit for the upstream Froude number is not constant for the formation of a maximum-wave jump – it depends on the relative drop height. Furthermore, the experimental results showed that the energy-dissipation ratios of maximum- and minimum-wave jumps are equal to or larger than those of classical hydraulic jumps. For this reason, wave-type jumps may be preferred at stilling basins with drops along with A-jumps. [ABSTRACT FROM AUTHOR]

This work presents an experimental study of the fluctuating properties of hydraulic jump rollers for high-Froude-number and pre-aerated inflow conditions, to investigate the validity of empirical relationships in the literature that are derived typically from experiments for smaller Froude numbers and clear-water approach flows. The jump roller fluctuations are evaluated in terms of the dimensions of the roller surface profile, the fluctuation magnitudes and frequencies of the instantaneous jump toe positions and water elevations, including at the tailwater surface, and the formation frequency and advection velocity of internal vortices in the shear layer. The effects of pre-aeration are found primarily in the length-scale properties such as jump length and surface fluctuation magnitudes, while the time-scale properties such as characteristic frequencies of the unsteady motions are not affected. Extrapolation of existing quantitative prediction of jump roller dynamic properties to high-Froude-number flow conditions should be performed carefully. An assessment of the fluctuating bubble counts within fixed time intervals yields close frequencies between the bubble grouping motions in the shear layer and the jump toe and tailwater wave motions, thus implying possible correlations between the roller surface deformations and air entrainment. [ABSTRACT FROM AUTHOR]

Oxygen is needed in water to maintain the natural ecological balance and the health of organisms. The amount of dissolved oxygen (DO) in water can be increased naturally in different ways. In particular, some hydraulic structures are designed so reoxygenation of water occurs spontaneously over a short distance and in a short time. Baffled chutes are designed to dissipate the energy of flow in irrigation systems, wastewater systems and stormwater systems. Staggered baffle blocks placed in a chute channel not only dissipate the energy of the water but also allow free oxygen transition between the water–air surface by means of hydraulic jumps. While water flows over, between and around the blocks, air bubbles are entrained into the water. The entrained air bubbles in the flow start to dissolve within the chute and the DO concentration in the water thus increases. In this study, the amount of DO was determined for baffle blocks with six different geometric shapes, different flow discharges and angle variations (10° ≤ α ≤ 56°). The oxygen transfer efficiency of the new baffle blocks designed in this study was found to be very effective. Different block types were found to have greater oxygen transfer efficiency for chutes with different slopes. [ABSTRACT FROM AUTHOR]

Some basic characteristics of a classic hydraulic jump flow over a pebbled rough bed, as well as on a smooth bed as a reference, are presented in this experimental study. For the experiments, an inflow Froude number Fr1 from 1.54 to 4.94 and inflow Reynolds number Re1 from 42 000 to 230 000 were considered. Visual observations and measurements suggested some differences between the formation of a hydraulic jump on rough and smooth bed configurations, including different air entrainment processes, larger vortical structures in the roller length and stronger backward flow in the upper layer. Furthermore, the jump roller and aerated flow lengths were shorter on a pebbled rough bed than on a smooth bed, while the dimensionless advection velocity of large vortices was the same for both bed types. The instantaneous jump toe perimeter showed the largest variation at the largest Fr1 and was generally larger on rough bed than on smooth bed. Larger oscillations of the free-surface profile were observed on smooth bed, highlighting that roughness resulted in smaller free-surface oscillations, suggesting the higher rate of energy dissipation. [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]

The effect of suspended sediment concentration on the characteristics of a hydraulic jump in a symmetrical trapezoidal channel was studied experimentally and compared with a classic jump. The first test series of the classical jump was performed in a rectangular flume, while the second series was conducted with two different trapezoidal side slopes. In both cases, the tests were conducted under clear water and with different concentrations (4, 8 and 12%) of fine sand of 0.22 mm as suspended sediment. The results of the tests showed that, with an increase in sediment concentration, the jump length ratio and the sequent depth ratio decreased and the energy dissipation increased. The present study considered three different sections (two sections of trapezoidal shape with side slopes of 60° and 75° and one rectangular section). A comparison of the results in flow with Fr1 = 10 for all three sections for a sediment concentration of 12% with clear water showed that the jump length ratio decreased by 14%, 22% and 18%, the sequent depth ratio decreased by 12%, 21% and 31% and the energy dissipation ratio increased by 9%, 12% and 11%, respectively. Some dimensionless relations for the prediction of jump characteristics were also developed. [ABSTRACT FROM AUTHOR]

A comprehensive study on free and submerged hydraulic jumps in different stilling basins was carried out. The effects of three adverse slopes, three bed roughnesses and three positive step heights on the hydraulic jump characteristics with a Froude number of 4·56–9·55 and a submergence factor of 0·1–1·5 were investigated. Two semi-theoretical solutions based on the momentum equation were developed to estimate the sequent depth ratio and the submerged depth ratio and the results were compared with experimental data. The results showed that the submerged depth ratio decreased by 22·3% compared with that of the classical jump. The lengths of the free and submerged hydraulic jumps were decreased by 47 and 32·1%, respectively, compared with the length of the classical jump. The maximum errors in the semi-theoretical estimations of the sequent depth ratio and the submerged depth ratio of free and submerged jumps were ±11% and ±16%, respectively. The thickness of the dimensionless boundary layer of the free and submerged jumps was determined to be 0·71 and 0·37, respectively. The average energy loss of the submerged jump in the conditions of this study was 10% more than that of the classical jump. [ABSTRACT FROM AUTHOR]

Flow characteristics downstream of free and submerged hydraulic jumps with and without blocks were experimentally studied for Froude numbers ranging from 3·48 to 6·85. The streamwise variation of the mean longitudinal velocity, turbulence intensity and turbulent kinetic energy as well as bed shear stress and water surface fluctuations were studied and compared for different flow regimes. Empirical equations are presented for longitudinal variations of the bed shear stress and water surface fluctuation for free and submerged jumps with and without blocks. The length required for the bed shear stress and water surface fluctuation to attain asymptotic magnitudes was used to define new characteristic lengths for hydraulic jumps. The results of this study show the effects of blocks in determining the longitudinal extension of hydraulic jumps. It was found that the presence of the blocks damped the streamwise variation of the studied flow parameters in a significantly shorter distance. It was also found that the deflected surface jet regime that occurred in submerged jumps with blocks had streamwise characteristics similar to those of free jumps with blocks. The results of this study confirm that this flow regime of submerged jumps can effectively be used as an energy dissipator within a stilling basin with a length approximately equal to that required for free jumps. [ABSTRACT FROM AUTHOR]

Side weirs are widely used for flow control and diversion. Although many studies on sub- and supercritical flows along these weirs have been conducted, only a few research studies have considered the generation of a hydraulic jump along the side weir. Spatially varied flow including a hydraulic jump along the rectangular side weir is studied in this paper. Experimental data for different weir geometries and hydraulic conditions are analysed. Based on the experimental results, new equations for estimating the jump length, the ratio of the conjugate depths and the discharge coefficient are presented. Also, the head loss due to the presence of a hydraulic jump is studied. Furthermore, a numerical model is developed for coupling the water surface profile with a hydraulic jump along the side weir. In this model the lateral outflow momentum is considered, which has been mostly ignored in previous works. The model predicts the location of the hydraulic jump. A comparison of the numerical and experimental results indicates good agreement. [ABSTRACT FROM AUTHOR]

In some cases, the flow head loss is not the main concern of design engineers, who instead prefer to exclude the hydraulic jump from super- to subcritical flow due to unfavourable flow conditions. The present study investigates the flow field and hydrodynamic aspects of the transitional region from super- to subcritical flow without a hydraulic jump. It is found that inside the transitional region the velocity and pressure profiles deviate slightly from uniform flow velocity and hydrostatic pressure. According to evaluation of the velocity measurements in conjunction with the continuity equation, the characteristics of the transitional region are determined. Furthermore, Reynolds stresses are analysed and the mechanisms of transition from super- to subcritical flow without a jump are demonstrated qualitatively. Results relating to the profiles of shear stresses, vorticity and the total angular momentum along the transition are developed. Results indicate that the first short part of the flow field downstream of the transition structure floats on the incoming high-speed fluid where the shear stress is maximal. It is observed that, downstream of the structure, both the shear stresses and the vorticity are maximal along the streamlines. Inside the shear layer, the vorticity spreads upward by diffusive mechanisms. [ABSTRACT FROM AUTHOR]

The article focuses on a study done in order to approximate the sequent depth ratio of the hydraulic jump formed in an arbitrary gradually expanding channel. It mentions that study made assumptions in quarter-elliptical longitudinal water surface profile and linear longitudinal water surface profile. The study found a linear longitudinal water surface profile.

Local scour downstream of stilling basins constitutes an important field of research in the context of the stability of hydraulic structures. This paper deals with the temporal and spatial evolution of local scour downstream of low-head spillways with a horizontal apron. Experiments were carried out in a 1 m wide and 20 m long rectangular channel. Three different, nearly uniform, sediments were used for the mobile bed. Tests were of long duration from 48 up to 196 h, but a few runs of short duration (1 or 3 h) were also carried out to better analyse the earlier scour stages. It was found that the main dimensionless parameters governing the scouring process are the tailwater densimetric Froude number, the relative time, and the relative distance of the toe of the hydraulic jump from the apron edge. Based on the experimental data, the salient features of the local bed morphology evolution are described through simple power-type equations. No experimental evidence was found in support of the similarity of scour profiles. [ABSTRACT FROM AUTHOR]

Accurate calculation of conjugate depths in a hydraulic jump is important to hydraulic design in open channels. Iterative formulae for calculating conjugate depths in hydraulic jumps in trapezoidal open channels were developed using mathematical transformation of the momentum equation. Two formulae that are adjusted from the critical depth of trapezoidal channels were proposed to compute the initial values for iterative formulae. The iterative formulae described here can be used for computer program development to find accurate solutions of conjugate depths. Because the appropriate initial values were selected to accelerate the convergence rates of iteration procedures, the output from the first iteration can be treated as a reliable estimate of conjugate depths with the relative error less than 0·8% in most cases. The approximation formulae are well-suited for manual calculations. [ABSTRACT FROM AUTHOR]

This study presents a novel, simple and accurate approximation of the eigenvalues of the sequent depth ratio of the hydraulic jump formed in an arbitrary gradually expanding prismatic channel. An iterative method is proposed to calculate the sequent depth ratio directly. The presented formulas are applicable to all ranges of side slopes and expansion angles for the channel. The prediction is compared with experimental data and earlier calculations for the range of expansion angles from 3 to 9° in a trapezoidal and rectangular expanding channel. The results indicate that the proposed method is accurate yet simple to use and free of empirical coefficients. [ABSTRACT FROM AUTHOR]

The gradually diverging stilling basin is attractive to the designer due to its compatibility with a large range of upstream and downstream sections, and to having a small sequent depth ratio and jump length. However, the hydraulic jump in such stilling basins often encounters instability and asymmetrical flow problems. In the present study, the effect of broad and sharp-crested sills in improving hydraulic jump characteristics, including sequent depth ratio, jump length and the free surface profile of a jump in a gradually diverging stilling basin was investigated. For this purpose, sills with various heights and different locations relative to the jump toe were installed in stilling basins with diverging angles of 3, 5 and 9°. In total, 284 tests were carried out in the range of initial Froude numbers of 3·1 to 10·4. The results indicate that the end sill has an insignificant effect on the sequent depth ratio, but it may considerably decrease the length of the hydraulic jump. It was also found that the sill could considerably improve the general conditions and features of an expanding hydraulic jump and could stabilise the position of this type of jump. [ABSTRACT FROM AUTHOR]

This paper presents the comparison between numerical results obtained with a conceptual model proposed in a companion paper and experimental results collected from previous studies. The numerical model is based on a finite difference approximation using the MacCormack scheme with a total variation diminishing high-resolution correction term for the mixture mass and momentum conservation equations and an artificial viscosity term for the sediment mass conservation equation. From the comparison between numerical and experimental results, it can be verified that the model generally gives results in good agreement with the experimental data and the wave structure is in accordance with what has been reported in previous studies. The estimation of model parameters based on existing sheet-flow data seems a promising way of developing models without arbitrary choice of values for tuning parameters. Some limitations can be identified, namely the equilibrium sediment transport approach implies that the model cannot simulate the hydraulic jump formed in the higher mobility bed for dry bed conditions. The use of a constant friction factor does not allow simulating the exact wave-front location for all instants in time. [ABSTRACT FROM AUTHOR]

Reliable prediction of upstream and downstream depths in a hydraulic jump is essential for hydraulic design in open channels. A series of algorithms is proposed for estimating the ratio of conjugate depths in a hydraulic jump in a horizontal channel over a range of Froude numbers and for a range of different trapezoidal and circular sections running part-full. By solving the momentum equation using appropriate values for the depth of centroid below the free surface, an iterative approach is proposed that uses the Newton-Raphson method and produces satisfactory agreement with recent published experimental data. The resulting graphs of conjugate depth ratio y2=y1 against F1 were also used to form the basis of a series of equations of best-fit lines that could be used as first approximations for use in hydraulic design problems. The results obtained were also used to predict the energy loss in the hydraulic jump. It is envisaged that the algorithms described here could be incorporated into standard design spreadsheets for use by practitioners involved in civil engineering hydraulics design. [ABSTRACT FROM AUTHOR]

A fuzzy logic model was constructed to predict hydraulic jump aeration efficiency. Fuzzy subsets and rules were created based on experimental observations and measurements carried out in a 0.5m wide flume with upstream Froude and Reynolds numbers of 2·3-6·4 and 1·4-5·4 × 104, respectively. A strong correlation was found between the aeration efficiency and Froude number. Upstream Froude and Reynolds numbers were selected as input parameters for the model. In this study, rather than mathematical equations, linguistic expressions were used to relate the upstream Froude and Reynolds numbers with aeration efficiency in an IF-THEN format. The proposed fuzzy model made good predictions and captured the system dynamic behaviour. Experimental observations confirmed the fact that hydraulic jump can be used as an aerator and mixing device in water treatment plants. Estimation of the aeration efficiency of a hydraulic jump could be made by any designer with the help of the fuzzy logic procedure described in this paper. [ABSTRACT FROM AUTHOR]

The design of a stilling basin structure involves an investigation of the river cross-section, determination of the water depth in the river, evaluation of the energy levels, definition of the downstream channel dimensions, calculation of flow depth and finally an analysis of hydraulic jump in the stilling basin. The equations that are used to determine the flow depths are non-linear and therefore required a time-consuming trial-and-error method to solve them. However, water depths may be found by utilising an iterative technique commonly referred to as the Newton-Raphson iteration technique, which is used to solve the system of non-linear equations. In this study, a computational model, based on the use of the Newton-Raphson technique to determine the flow profile of the hydraulic jump type stilling basin, is developed. A numerical example for using the computational model, depending on a prepared computer program, is presented. [ABSTRACT FROM AUTHOR]

The article presents a discussion related to the influence of impinging jets on hydraulic jumps. Experiments were carried out in a horizontal channel with a free jump and jumps with jets introduced at various angles. Particles within the jumps were traced using a high-speed video camera and the images were processed using a computer to determine particle velocities within the jumps. A simple numerical model using Strip Integrals across the flow is used to predict the kinematic characteristics of such jumps.

An introduction is presented in which the editor discusses various reports within the issue on topics including aquatic plants and the regime of flow of an open channel, sequent depth of a hydraulic jump in an open channel and flood routing model.

The article discusses papers within the March 2012 issue of "Proceedings of ICE: Water Management," including a paper that offers a new approach to describe the surface profile of a hydraulic jump formed in an open channel of arbitrary cross-section.

An introduction is presented in which the editor discusses various reports within the issue on topics including the morphological evolution of a river insider a sharp bend, failure mechanisms of riprap placed on an apron, and the hydraulic jump in expanding channels.

This article responds to a paper which developed a fuzzy logic model to forecast the efficiency of hydraulic jump aeration. It asserts the need for further clarification in both the paper's application of methodology and results. It observers that the paper's authors did not follow the required procedure for developing the model. The article notes that the authors applied a trial and error approach to determine the membership function.

The article presents a study of air entrainment and oxygen transfer in high-head gated passages. It relates on how hydrodynamic processes such as hydraulic jumps and stepped channels promotes oxygen transfer from air to water although they possess strong turbulence, local scouring and energy dissipation. However, it notes that formation of hydraulic jumps causes undesirable effects to close conduits, thus, asserting on using either of its aeration efficiency or dimensionless parameter.