Showing papers in "Journal of Hydraulic Research in 1995"
TL;DR: In this paper, experimental and numerical results concerning the flow induced by the break of a dam on a dry bed are presented, which consists of a shock-capturing method of the Godunov type.
Abstract: Experimental and numerical results concerning the flow induced by the break of a dam on a dry bed are presented. The numerical technique consists of a shock-capturing method of the Godunov type. A physical laboratory model has been employed to infer properties and validity of the numerical solution. Attention is also given to the applicability of the mathematical model, based on the shallow water equations, to this class of problems.
361 citations
TL;DR: In this article, the effect of a sloping bed on the direction of sediment transport is determined by conducting bed-levelling experiments, and a distinction is made between laboratory conditions and natural rivers.
Abstract: Laboratory experiments have been conducted to provide data for modelling the direction of sediment transport on a transverse sloping alluvial bed. Conditions with prevailing bed-load transport, and conditions in which a significant part of the bed material is transported as suspended-load are studied. The effect of a sloping bed on the direction of sediment transport is determined by conducting bed-levelling experiments. Comparison of the results with data of curved flume experiments and experience gained with numerical computation of the bed topography in natural rivers yields the conclusion that, at least for bed-load transport, a distinction should be made between laboratory conditions and natural rivers. For conditions with suspended sediment transport the transverse slope effect can not be modelled identical as for bed-load transport.
262 citations
TL;DR: In this paper, a weighting function model of transient friction is developed for flows in smooth pipes by assuming the turbulent viscosity to vary linearly within a thick shear layer surrounding a core of uniform velocity and is thus applicable to flows at high Reynolds number.
Abstract: Two of the most promising analytical models of unsteady friction in turbulent pipe flows are based on sharply contrasting hypotheses. One uses the history of the flow; the other uses instantaneous conditions. The purposes of this paper are to present an analysis using the former approach and to indicate how to determine which of the two methods is appropriate. A weighting function model of transient friction is developed for flows in smooth pipes by assuming the turbulent viscosity to vary linearly within a thick shear layer surrounding a core of uniform velocity and is thus applicable to flows at high Reynolds number. In the case of low Reynolds number turbulent flows and short time intervals, the predicted skin friction is identical to an earlier model developed by Vardy et al (1993). In the case of laminar flows, it gives results equivalent to those of Zielke (1966, 1968). The predictions are compared with analytical results for the special case of flows with uniform acceleration. It is this case that ...
209 citations
TL;DR: Two high-resolution numerical schemes based on Lax-Friedrichs numerical flux and ENO type of extrapolation are presented for the computation of free-surface flows and the ease of implementation makes the new method very attractive for practical applications.
Abstract: Two high-resolution numerical schemes based on Lax-Friedrichs numerical flux and ENO type of extrapolation are presented for the computation of free-surface flows. The performances of these schemes are similar to other high-resolution (TVD and ENO) schemes. However, the ease of implementation makes the new method very attractive for practical applications. The first numerical scheme is afterwards modified to account for the presence of the bottom slope terms. Several applications are presented.
176 citations
TL;DR: In this paper, a nodal point relation at bifurcations is proposed for one-dimensional (ID) network morphodynamic models: the ratio between the sediment transports into the downstream branches is proportional to a power of the discharge ratio.
Abstract: Based on model-technical as well as physical considerations a nodal-point relation at bifurcations is proposed for one-dimensional (ID) network morphodynamic models: the ratio between the sediment transports into the downstream branches is proportional to a power of the discharge ratio. The influence of the nodal-point relation on the behaviour of the morphodynamic model is analyzed theoretically. The exponent in the nodal-point relation appears to be crucial for the stability of the bifurcation in the model. For large values of the exponent, the bifurcation is stable, i.e. the downstream branches remain open. For small values of the exponent, the bifurcation is unstable: only one of the branches tends to remain open. The exponent also has a strong influence on the morphological time scales of the network. The conclusions from the analysis have been verified by numerical simulations using a package for one-dimensional network modelling.
142 citations
TL;DR: In this paper, a porosity model is developed to model the bed roughness elements, which are large stones and rocks in the rivers, and a finite volume method is used to solve the Navier-Stokes equations for three dimensions on a general nonorthogonal grid.
Abstract: A numerical model for three-dimensional simulation of water flow in rivers with large roughness elements is developed. The bed roughness elements are large stones and rocks in the rivers. The model uses a finite volume method to solve the Navier-Stokes equations for three dimensions on a general non-orthogonal grid. The k-e turbulence model is used to solve the Reynolds-stress term. A porosity model is developed to model the bed roughness elements. The porosity model is used in combination with the solution of the Navier-Stokes equations to calculate interactions between porous and non-porous areas. To test the model, a reach of the Norwegian river Sokna is modelled. Velocity measurements from the river are taken at a number of locations and at several discharges. The measured velocities compare well with the results from the numerical model.
117 citations
TL;DR: In this article, a large eddy simulation of turbulent flow in a compound open channel with one floodplain is reported for a Reynolds number of approximately 42000, which is in good agreement with experimental measurements and previous numerical calculations.
Abstract: A Large Eddy Simulation of turbulent flow in a compound open channel with one floodplain is reported for a Reynolds number of approximately 42000. The results are in good agreement with experimental measurements and previous numerical calculations. The mean velocity field, secondary circulation field, bed stress distribution, and lateral stress distribution are presented in detail.
92 citations
TL;DR: In this article, a critical study of hydraulic jumps, submerged jumps and plane turbulent wall jets as a class of similar flows is presented, with the hydraulic jump and the wall jet forming the transition state in between.
Abstract: This paper presents a critical study of hydraulic jumps, submerged jumps and plane turbulent wall jets as a class of similar flows. Using the experimental results available in the literature as well as some new results, the hydraulic jump and the wall jet are shown to be the end states with the submerged jumps forming the transition state in between. The three properties considered are the similarity of the velocity distribution, decay of the velocity scale and the growth of the length scale. The velocity distribution is approximately the same for all the flows. Using a longer length scale L, the decay of the velocity scales for the end states has been redefined and for submerged jumps, the decay has been found to be either free-jump-like (FJL) or wall-jet-like (WJL). The variation of the length scale L was found to have distinctive variations for the different flows. Some new results are also presented for the reverse flow field of submerged jumps.
84 citations
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TL;DR: In this paper, the authors present a critical analysis of the energy loss at drops, using the results of an experimental study on three drops, several assumptions made by White and Gill in developing an equation.
Abstract: This paper presents a critical analysis of the energy loss at drops. Using the results of an experimental study on three drops, several assumptions made by White and Gill in developing an equation ...
83 citations
TL;DR: In this article, the results of simulations of the flow near spur dikes using a three dimensional numerical model are presented and compared with flume measurements conducted at the Franzius Institute in Hannover, Germany.
Abstract: The objective of this paper is to show the results of simulations of the flow near spur dikes using a three dimensional numerical model. Special attention was given to the simulation of the wake formed downstream of the dyke and the influence of the eddy viscosity field on velocities, flow depths and reattachment lengths. The most important features of the model are described. Comparisons with flume measurements conducted at the Franzius Institute in Hannover, Germany are also presented.
72 citations
TL;DR: In this article, a two-dimensional (horizontal) numerical model of water and sediment motion for steady-state conditions was used to calculate the general bend scour and a new equation for a maximum scour depth prediction at groynes located along an outer bank of a bend was introduced.
Abstract: This paper provides some results of field investigations of bed topography and local scour at groynes in two bends of the Warta River. Concave banks of these bends are protected by impermeable groynes oriented upstream with almost constant spacing and geometric shape. Both bed topography in bends and local scour holes at the groyne heads were formed by channel flows equal to or smaller than the mean annual discharge. A two-dimensional (horizontal) numerical model of water and (bed-load) sediment motion for steady-state conditions was used to calculate the general bend scour. A new equation for a maximum scour depth prediction at groynes located along an outer bank of a bend is introduced. The maximum scour depth occurs inside the groyne field. This local scour is a function of a depth and depth-average flow velocity along the concave bank, spacing and location relative to the bend, and orientation to flow.
TL;DR: In this paper, a particle tracking velocimetry (PTV) based method was developed for obtaining surface-velocity fields in unsteady flows which is useful for hydraulic model studies.
Abstract: A method has been developed for obtaining surface-velocity fields in unsteady flows which is useful for hydraulic model studies. The method is based on the established technique of Particle Tracking Velocimetry (PTV) but unlike other whole-field systems is suitable for use over relatively wide areas. Results are presented from its application to flows around conical model islands with uniform sloping sides from which strong vortex shedding occurs. To allow an assessment of accuracy, simultaneous LDA measurements were taken in the wake of an island and comparisons of velocity prediction are presented.
TL;DR: In this paper, the authors reviewed all the approaches of non-uniform sediment transport in rivers and treated mass balance equations in the same way as Reynolds decomposition for turbulent motion: instantaneous variables are decomposed in the average, over a large number of realizations, and in the fluctuating pan.
Abstract: In the paper die concept of active (or mixing) layer, on which almost all the approaches of non-uniform sediment transport in rivers are based, is reviewed. Accounting for bed level fluctuations, mass balance equations are treated in the same way as Reynolds decomposition for turbulent motion: instantaneous variables are decomposed in the average, over a large number of realizations, and in the fluctuating pan. The resulting equations are correct from a theoretical point of view and have precise physical meanings. The theoretical findings are compared to some experimental data by Ribberink [1987].
TL;DR: In this paper, moment-based similarity functions were applied to finite difference solutions of the transient storage equations, in order to investigate the relationship between these approaches, and the results indicated fairly good agreement.
Abstract: Solute concentrations in streams due to instantaneous slug releases are frequently influenced both by decay and by exchange with dead zones, among others. Based on the transient storage equations with first-order decay terms, explicit relationships are given for the computation of the zeroth to third temporal moments. The equations presented were applied within the framework of moment-based similarity functions which yield approximate temporal distributions of concentration. Results thus obtained were subsequently compared to finite difference solutions of the transient storage equations, in order to investigate the relationship between these approaches. Within the previously established ranges of applicability of the two similarity functions employed the comparisons indicated fairly good agreement.
TL;DR: In this paper, a 3D numerical model has been developed to investigate transport processes of solute in a compound open channel and the Navier-Stokes equations have been numerically solved in conjunction with the linear and nonlinear k-∊ models to predict flow fields and turbulent parameters.
Abstract: A 3-D numerical model has been developed to investigate transport processes of solute in a compound open channel. The Navier-Stokes equations have been numerically solved in conjunction with the linear and nonlinear k-∊ models to predict flow fields and turbulent parameters. The predicted velocity field and eddy viscosity are then used for solving the solute transport equation to predict solute transport rates. The hydrodynamic and solute transport models have been applied to the experimental studies undertaken by Wood and Liang (1989) and the results obtained from both the linear and non-linear k-∊ models are compared with their results. This comparison clearly shows the influence of the secondary currents upon the mixing processes.
TL;DR: In this paper, Bed-shear stress in non-uniform and unsteady open-channel flows is studied. But the authors focus on the nonuniform flow.
Abstract: (1995). Bed-shear stress in non-uniform and unsteady open-channel flows. Journal of Hydraulic Research: Vol. 33, No. 5, pp. 699-704.
TL;DR: In this paper, the main flow characteristics of undular jumps are established based on previous and present observations, including surface characteristics along the axis and the walls of the rectangular channel, and generalized surface profiles are presented.
Abstract: The differences between the undular jump and the undular surge are described. Further, the limit approach flow depth and the channel width are defined for undular jumps governed by the Froude similarity law. Based on previous and present observations, the main flow characteristics of undular jumps are established. These include surface characteristics along the axis and the walls of the rectangular channel. Also, generalized surface profiles are presented. Finally, the formation of shocks is physically explained as a breakdown of the supercritical approach flow.
TL;DR: In this article, a finite element computational algorithm for the solution of one-dimensional, unsteady turbidity currents is presented, where layer-averaged governing equations form a hyperbolic system consisting of three equations, namely continuity and momentum equations for the flow, and mass conservation equation for the sediment.
Abstract: A finite element computational algorithm for the solution of one-dimensional, unsteady turbidity currents is presented. The layer-averaged governing equations form a hyperbolic system consisting of three equations, namely continuity and momentum equations for the flow, and mass conservation equation for the sediment. Tracking the front of a propagating turbidity current is akin to the problem of predicting the propagation of a dam-break wave over a dry bed. The standard Galerkin formulation does not give good results when applied to the highly nonlinear flow regime near the front, so the dissipative-Galerkin technique (Petrov-Galerkin technique) which has a selective damping property, is used. The numerical model is applied to the case of a turbidity current developing along a sloping bottom. The computed results compare favorably well against both the relationship proposed by Britter and Linden (1980) to estimate the speed of density currents fronts and the experimental observations made by Altinakar, Gr...
TL;DR: In this article, the frequency downshift of swash oscillations compared to incident waves is examined by laboratory experiments and numerical simulations in connection with the uprush-backwash interaction in the s...
Abstract: The frequency down-shift of swash oscillations compared to incident waves is examined by laboratory experiments and numerical simulations in connection with the uprush-backwash interaction in the s...
TL;DR: In this paper, the numerical solutions for the buoyant spreading flow with a drag-like arresting mechanism at the density front are used to predict the overall properties of the spreading motion for different ambient conditions.
Abstract: Buoyant upstream spreading forms part of the more or less radial spreading motion that occurs when a continuous buoyancy source exists within a weak ambient flow. Such buoyancy source may be located at the water surface, or bottom, or at a terminal level within an ambient density stratification, and follows the initial mixing phase of a pollutant discharge. The upstream spreading flow stagnates against the oncoming ambient flow, and is ultimately diverted in the downstream direction. The numerical solutions by Jones, Jirka and Caughey (1983) for the buoyant spreading flow with a drag-like arresting mechanism at the density front is used to predict the overall properties of the spreading motion for different ambient conditions. Data from laboratory experiments and from field observations are in good agreement with the model predictions.
TL;DR: In this paper, a simulation model for the formation and evolution of frazil in open channels is developed, where the primary nucleation is assumed to be due to mass exchange of seeding crystals at the free surface.
Abstract: A simulation model for the formation and evolution of frazil in open channels is developed. In this model, the primary nucleation is assumed to be due to mass exchange of seeding crystals at the free surface. The model of frazil crystals growth is based on the rate of heat transfer between crystals and the ambient turbulent flow. Secondary nucleation and flocculation are simulated based on binary collisions of frazil particles. The model is validated with existing experimental data. It is capable of simulating the variation of water temperature during the frazil formation period and the evolution of size and concentration distributions of frazil in the flow. Effects of the surface heat exchange, the rate of seeding, and the flow condition are examined.
TL;DR: In this article, the authors analyzed the conditions of filling for ten aerator geometries and found that the cavity filling occurs when the Froude number is less than a critical value or when the ratio of the flow depth over the total offset is larger than a characteristic value.
Abstract: Cavitation damage to spillway surfaces may be prevented with the use of aeration devices. These serve to introduce air into the layers close to the channel bottom in order to reduce cavitation erosion. Under some circumstances, the aerator can be drowned out, will cease to protect the spillway surface, and act potentially as a cavitation generator. This article analyses the conditions of filling. Then experimental data for ten aerator geometries are reviewed. Depending upon the aerator geometry, the cavity filling occurs when the Froude number is less than a critical value or when the ratio of the flow depth over the total offset is larger than a characteristic value.
TL;DR: In this article, one-dimensional and two-dimensional laser Doppler Velocimeter (LDV) measurements were used respectively to measure velocity of smooth-wall open channel flows with channel bed slopes varying between 0.25% and 3%.
Abstract: One-dimensional and two-dimensional Laser Doppler Velocimeter (LDV) were used respectively to measure velocity of smooth-wall open channel flows with channel bed slopes varying between 0.25% and 3%. Turbulent flows were all supercritical with Froude numbers varying from 1.5 to 3.5 and Reynolds number having a magnitude of 105. Using 1-D LDV the law of the wall and the law of the wake were examined and the von Karman constant K was verified to be 0.4 universally, while the integral constant A might change with distance from the side wall. The law of the wake exists clearly with a wake strength Π of about 0.3. Moreover, from the 2-D LDV measurements, the influence of channel slopes on the turbulent characteristics were fully investigated.
TL;DR: In this article, a split-operator approach is employed in the model with the advective terms solved by the minimax-characteristics method and the turbulence stress terms have been examined in detail and three important components established, including bottom generated turbulence, jet induced turbulence and momentum dispersion due to the vertical integration of the secondary motion arising from the horizontal curved flow.
Abstract: A depth integrated numerical model has been refined to simulate the tidal flows in a model square harbour. The harbour entrance width is narrow and of similar dimensions to the mean water depth. The advective accelerations and the turbulence stress terms of the governing hydrodynamic equations are therefore significant in describing the complex flow patterns. A split-operator approach is employed in the model with the advective terms solved by the minimax-characteristics method. The turbulence stress terms have been examined in detail and three important components established, including: bottom generated turbulence, jet induced turbulence and momentum dispersion due to the vertical integration of the secondary motion arising from the horizontal curved flow. An order of magnitude estimation has shown that the momentum dispersion is of primary importance. A simple zero order turbulence model has been used to account for the three mechanisms, with a semi-slip boundary condition being included to cater for t...
TL;DR: In this paper, a time-dependent wave equation is developed for waves propagating over permeable rippled beds taking account of the effects of porous medium, where the mean water depth and the thickness of porous layer are taken into account.
Abstract: A time-dependent wave equation is developed for waves propagating over permeable rippled beds taking account of the effects of porous medium. The mean water depth and the thickness of porous layer ...
TL;DR: In this paper, data from turbulent flows over steep-sided trapezoidal trenches and a backward-facing step in an open channel were used to assess the performance of three alternative models of turbulence viz. the industry-standard k-∊ model, a second-order closure which is linear in the Reynolds stresses and another which is quadratic in the same quantities.
Abstract: Data from turbulent flows over steep-sided trapezoidal trenches and a backward-facing step in an open channel were used to assess the performance of three alternative models of turbulence viz. the industry-standard k-∊ model, a second-order closure which is linear in the Reynolds stresses and another which is quadratic in the same quantities. The computations were carried out on body-fitted coordinates and were carefully checked for numerical accuracy. It is demonstrated that the mean-flow parameters are predicted equally well by all models but that the details of the turbulence structure are best captured by the second-order closures. The significance of these results to the practical prediction of trench flows is discussed.
TL;DR: In this paper, a large eddy simulation of steady uniform flow in a symmetric compound channel of trapezoidal cross-section with flood plains at a Reynolds number of 430,000 was presented.
Abstract: This paper dcsribes a Large Eddy Simulation of steady uniform flow in a symmetric compound channel of trapezoidal cross-section with flood plains at a Reynolds number of 430.000. The simulation captures the complex interaction between the main channel and the flood plains and predicts the bed stress distribution, velocity distribution, and the secondary circulation across the floodplain. The results are compared with experimental data from the SERC Flood Channel Facility at Hydaulics Research Ltd, Wallingford, England.
TL;DR: In this paper, two different numerical schemes, Mac- Cormack (second-order accurate in space and time) and two-four (fourth order accurate in time and second-order accuracy in space) were used with grid adaptation to numerically simulate the hydraulic jump at different Froude numbers in a rectangular channel.
Abstract: In a hydraulic jump, the supercritical flow suddenly changes to subcritical flow forming steep gradients of flow depth and velocity. In the numerical simulation of this flow, proper grid distribution can play a crucial role in the prediction and resolution of the solutions. In this paper, two different numerical schemes - Mac- Cormack (second-order accurate in space and time) and two-four (fourth-order accurate in space and secondorder accurate in time) -are used with grid adaptation to numerically simulate the hydraulic jump at different Froude numbers in a rectangular channel. Rai and Anderson's method is used to determine the grid speed; however, a different partial differential equation based on the conservative principle of grid arc lengths for clustering the grid points in one-dimensional flow is used along with the Boussinesq equations to simulate the flow. A number of tests were conducted at different Froude numbers tot confirm published data. The numerical results of the flow solutions are presen...
TL;DR: In this article, an approximate equation for wall shear stress in unsteady laminar pipe flows in terms of the instantaneous section mean velocity and acceleration is derived for two types of pressure gradient functions, a transient start-up flow and a linearly reversing pressure gradient.
Abstract: An approximate equation is derived for wall shear stress in unsteady laminar pipe flows in terms of the instantaneous section mean velocity and acceleration. The equation, which is exact for a constantly accelerating or decelerating flow, is applied to solve for two types of pressure gradient functions, a transient start-up flow and a linearly reversing pressure gradient. Comparison with exact analytical solutions verifies that the equation is adequate for the two types of transient flows investigated, and for low frequency oscillating flows.