Abstract of Papers - JHR Volume 41, 2003
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ISSUE NO. 1

An improved method for roughening floodplains on physical river models
 by ROBERT H. J. SELLIN, THOMAS B. BRYANT and JOHN H. LOVELESS
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Physical (hydraulic) modelling of river systems subject to overbank flow require the simulation of floodplain roughness. Significant full and reduced scale experiments have now been carried out to establish the flow resistance of a range of real and simulated floodplain vegetation. One use for this improved knowledge of floodplain hydraulics is to provide a basis for an improved method for overbank roughening in hydraulic models. It can also be of value in multi-dimensional numerical models The first part of this paper reviews briefly this work on floodplain vegetation resistance, leading to both empirical and theoretical relationships to describe floodplain roughness, and assesses the appropriate use of these methods. The second and greater part of the paper examines in more detail two methods used recently to roughen floodplains in large scale hydraulic models: non-submerging vertical rods, and a method based on expanded aluminium mesh units. A comparison is made between these two methods by reference to recent tests in the UK Flood Channel Facility at HR Wallingford. Practical recommendations are made for designing a roughness system appropriate for use in future river model tests.
 
 
Hydraulic classification of irrigation supply systems
 by RAHMAN H. KHATIBI
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Modern irrigation supply systems have diversified and yet methods of their classification have been overlooked. Thus, each system appears unique and this makes it difficult to integrate experience gained from their analysis. This paper postulates that ‘‘hydraulic command’’ is responsible for their diversification and creates ‘‘generic’’ variations among irrigation systems with each command method making up one class; conversely the systems associated with the same class or hydraulic command share the same generic complexities. The benefits of classification are methodological and include (i) gaining an insight into technical/ management issues associated with each class; (ii) obtaining an overview of generic variations across the classes of these systems enabling integration of knowledge; (iii) explaining mutual incompatibility of the systems associated with different command methods.


Bottom friction and time-dependent shear stress forwave-current interaction
 by JOSÉ S. ANTUNES DO CARMO, ANDRÉ TEMPERVILLE and FERNANDO J. SEABRA-SANTOS
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Bottom shear stresses in the wave-current interaction case are calculated using a numerical turbulent-closure model of the K-L type, where K is the turbulent kinetic energy and L is the length scale of the turbulence. Parameterized results of the friction coefficient are obtained in the case of a rough turbulent flow, as presented by Soulsby et al. [14], and these are here extended to the case of a smooth turbulent flow. Several comparisons with experiments and other results presented in the literature, particularly by Tanaka and Thu [19], show close agreement. A new parameterization of the time-series shear stress is proposed that includes a local friction coefficient and yields better results than the parameterization suggested by Soulsby et al. [14].

 Tailwater level effects on flow conditions at an abrupt drop
 by MICHELE MOSSA, ANTONIO PETRILLO and HUBERT CHANSON.
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This paper presents an experimental study of the transition from supercritical to subcritical flow at an abrupt drop. The paper reports a wide range of experimental conditions and the relevant regime charts. Long-term experimental results show that some flow configurations tend to behave quasiperiodically (i.e. oscillating flow patterns). The experimental results have direct implications on the design and construction of spillway stilling basins where abrupt drops may be used to stabilise the position of the jump. The present study proposes design guidelines taking into account the different flow types, for a range of tailwater flow conditions. These guidelines are essential for a safe and proper operation of stilling basins with abrupt drop.


Vortex chamber diodes as throttle devices in pipe systems. Computation of transient flow
by DR.-ING. FRIEDER HAAKH.
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A theoretical solution for the computation of transient flows in a pipe system with a vortex chamber diode, based on an energy balance and including an algorithm for numerical application in water-hammer programs, is presented. Moreover, the experimental results of several case studies provide a dimensioning concept.


Water drop erosivity: Effects on soil splash
 by L. MOUZAI and M. BOUHADEF.
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Detachment and transport of soil particles by water drop impact can be analysed in terms of the kinetic energy (1/2 MV2), or momentum (MV) of the water drop. Therefore density, diameter, fall height, velocity of the water drop and area of impact need to be considered. The drop impact pressure, which is the mathematical combination of these characteristics, has been interacted with soil splash characteristics such as the amount, the mass distance distribution and the mean distance. A splash board divided into 13 concentric compartments to collect the splashed particles and different capillaries produced drops with diameters between 3.7mm and 5.8mm formed the basis of the laboratory work.
The results shown that the involvement of the drop diameter steepened the curves representing the relationship between soil splash and drop pressure, which means that the drop diameter has an effect on soil splash. But, according to the correlation analysis, the involvement of the diameter did not improve the coefficient of determination of the relation between drop pressure and soil detachment except for the exponential function. In addition, the relationships between drop pressure and soil splash characteristics are mostly presented by a power functions.


Direct visualisation of underwater phenomena in soil-fluid interaction and analysis of the effects of an ambient pressure drop on unsaturated media
 by H.J. KÖHLER and M.A. KOENDERS
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A description is given of an apparatus in which a wide range of hydraulic conditions can be realised. A unique observation system using optical fibre based ‘endoscopes’ and an imaging system that includes a signficant digital processing element enables the visualisation of grain and fluid motion as well as air bubble behaviour in granular deposits of specified composition and geometry under externally imposed hydraulic conditions. Examples are given and a particular application in which a soil is studied that is fluidized by an external pressure drop. A description of the fluidized behaviour is given and the outcomes are cast in terms of a mathematical/physical model for fluidized material. This model is then used to predict the extent of a fluidized region in a one-dimensional situation.


 Analysis and numerical simulation of a single-well tracer test inhomogeneous,layered and slightly tilted formations
 by DR.AMRO M.M. ELFEKI.
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Simulation of a fleld tracer experiment from an injection well in an axially symmetrical flow field in homogenous, stratified and slightly tilted aquifers
is presented. The simulation has been verified by analytical solutions of the evolution of the first and second radial spatial moments of the tracer displacements derived in the current study under pure advective transport in case of layered formation. The study focused also on the discrepancies in the transport mechanisms between uniform (linear) and axially symmetrical radial flow fields in homogenous, layered and slightly tilted formations. Excellent agreement exists between analytical solution and the numerical simulation for the case of pure advection in both first and second moments supporting the validity of the numerical simulations.Asubdiffusive dispersion regime in case of transport by advection and dispersion in homogeneous aquifer is observed due to the decline of the velocity field. Ki is the representative effective medium of the layered aquifer in case of pure advection under axially symmetrical flow field.
 
 
Methods for vibro-acoustic diagnostics of turbine cavitation
 by BRANKO BAJIC.
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Basic aspects of noise sampling, signal processing and analysis, and data processing, analysis, and interpretation in vibro-acoustic diagnostics of turbine cavitation are investigated in a series of prototype and model experiments. Several weak points of the practice are identified, and improvements and new techniques are developed. These techniques enable extraction of data on cavitation details and early detection of detrimental effects met in turbine exploitation. A brief review of weak points of the practice, developed improvements, and new techniques, as well as examples of application, are presented in the paper.


 Control of hydraulic jump by sill in aU-shaped channel
 by BACHIR ACHOUR and MAHMOUD DEBABECHE
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The control of a hydraulic jump by both thin-crested and broad-crested sills in a U-shaped channel is examined theoretically and experimentally. Under certain simplifications, the theoretical development results in explicit relations for the relative sill height, by including the effect of approach velocity. This also leads to a similar condition for the control by a sill in the rectangular channel, by extension of the Forster and Skrinde approach. A particular study is presented to define the conditions required for the minimum height of a broad-crested sill. Finally, the relative length of jump is quantified by accounting for the relative depth of the approaching flow.

A non-touch sensor for local scour measurements
 by FRANCESCO BALLIO and ALESSIO RADICE.
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A diffuse light intensity photocell coupled with a fiber optic was tested as a non-touch switch sensor for bottom profiling. The device is inexpensive and robust. When mounted on a mechanical positioning carriage it allows continuous scour measurements underwater. Only the fiber optic is immersed in water; therefore the sensor is little intrusive and can be easily used in proximity of side walls. Control tests on a fixed shape showed that the accuracy of the system is appropriate for measurements of local scours. The apparatus was successfully used during mobile bed scour experiments, allowing highly detailed measurements.

 

ISSUE 2

A multiphase oil spill model
 By Pavlo Tkalich, Md. Kamrul Huda and Karina Yew Hoong Gin
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A multiphase oil spill model has been developed to simulate consequences of accidental oil spills in the marine environment. Six state variables are computed simultaneously: an oil slick thickness on the water surface; concentration of dissolved, emulsified and particulate oil phases in the water column; and concentration of dissolved and particulate oil phases in the bottom sediments. A consistent Eulerian approach is applied across the model, the oil slick thickness is computed using the layer-averaged Navier–Stokes equations, and for transport of the oil phases in the water column the advection–diffusion equation is employed. The kinetic terms are developed to control the oil mass exchange between the variables. The governing equations are verified using test cases, data and other models. The model is useful for short and long-term predictions of the spilled oil dynamics and fate, including application of the oil combating elements, such as chemical dispersants and booms.

Progradational sand-mud deltas in lakes and reservoirs. Part 1. Theory and numerical modeling
 By Svetlana Kostic and Gary Parker
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Deltas are cone-shaped deposits formed at the confluence of rivers with standing bodies of water. One of the most common stream morphologies associated with deltas is that of the sand-bed stream. Such streams usually carry significantly more mud as wash load than they do sand as bed material load. Deltas typically form so that the sand deposits fluvially in the river channel and avalanches into deeper water to create a prograding delta face. The remaining muddy river inflow often plunges over the steep delta face and continues flowing downslope as a bottom turbidity current. The mud carried into deep water by the underflow settles out on the bed of the lake or reservoir. A variety of numerical models dealing separately with either fluvial deposition or depositional turbidity currents have been proposed to date. The work reported here pertains to an integral, physically-based, moving boundary model of deltaic sedimentation in lakes and reservoirs that captures the co-evolution of the river-delta morphology and the associated deposits. The formulation unites fluvial and turbidity current morphodynamics in a single numerical model. The model is tested against the results of the two experiments described in a companion paper.

Progradational sand-mud deltas in lakes and reservoirs. Part 2. Experiment and numerical simulation
 By Svetlana Kostic and Gary Parker
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Rivers deposit deltas wherever they reach standing water, i.e. a lake or reservoir. Here the case of a sand-bed river carrying mud as wash load is considered. In general the sand tends to deposit out to form a fluvial topset and an avalanching foreset, and the mud tends to deposit out as a bottomset. During floods, many sand-bed rivers carry sufficiently high concentrations of washload to render the river water heavier than that of the body of standing water. In such a case the mud-laden river flow plunges to form a bottom turbidity current. In a companion paper a 1-D numerical model of a prograding delta was presented. In this model fluvial, avalanching and turbidity current deposition are all linked in terms of a moving boundary formulation. Here the model is compared against two experiments on delta progradation. The experiments reveal an intriguing interaction between the three elements of the model, with foreset progradation burying the bottomset and pushing its upstream point ever downstream, and with bottomset deposition raising the toe of the foreset, so increasing the rate of foreset progradation as sand is delivered from the topset. The numerical model of the companion paper captures this interaction with a minimum of adjustment of input parameters. The resulting description of delta morphodynamics is very similar to that observed in e.g. the delta in the Colorado River, USA where it reaches Lake Mead.

Transverse mixing in sinuous natural open channel flows
 By J.B. Boxall, I. Guymer and A. Marion
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Accurate modelling of transport and mixing of solutes within natural watercourses is vital for environmental management. A lack of understanding of the dominant processes, particularly quantification of transverse mixing processes in natural channels, severely limits the accuracy and usefulness of such modelling. This paper presents results from tracer and hydrodynamic studies conducted on a ‘natural’ channel form under laboratory conditions. The measurements are analysed using the standard method of moments and the variation of the resulting mixing coefficients examined with respect to the variations in the natural channel geometry and hydrodynamic measurements. Normalisation of the resulting transverse mixing coefficients is investigated. The work conclusively shows that the transverse mixing coefficient varies in direct relation to channel curvature, the variation is cyclic with meander geometry.

Finite volume method for simulating extreme flood events in natural channels
 By alerio Caleffi, Alessandro Valiani and Andrea Zanni
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The need for mitigating damages produced by extreme hydrologic events has stimulated the European Community to fund several projects. The Concerted Action on Dam-break Modelling workgroup (CADAM) performed a considerable work for the development of new codes and for the adequate verification of their performance. In the context of the CADAM project, a new 2D computer code is developed, tested and applied, as described in the present paper. The algorithm is obtained through the spatial discretisation of the shallow water equations by a finite volume method, based on the Godunov approach. The HLL Riemann solver is used. A second order accuracy in space and time is achieved, respectively by MUSCL and predictor–corrector techniques. The high resolution requirement is ensured by satisfaction of TVD property. Particular attention is posed to the numerical treatment of source terms. Accuracy, stability and the reliability of the code are tested on a selected set of study cases. A grid refinement analysis is performed. Numerical results are compared with experimental data, obtained by the physical modelling of a submersion wave on a portion of the Toce river valley, Italy, performed by ENEL–HYDRO and considered as representative of a real life flood occurrence.

A one-layer model to predict the time development of static armour
 By R. Bettess and A. Frangipane
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The development of static armour has been studied extensively from a number of different points of view. Given the hydraulic conditions and the initial composition of the bed, many relations have been proposed which predict the armoured distribution which develops.
There are fewer relations which predict the development of the armour layer in time and the change in transport rate as the armour develops.
An attempt is made in this paper to use a simple, one-layer model to predict the development of static armour and a comparison is presented with results obtained using different transport formulae for non-uniform sediments.
It is shown that a simple model based on the propagation of kinematic waves can predict the development of self-armoured beds by simulating the variations in sediment transport rate at the downstream end of a laboratory flume and in predicting the composition of the static armour that is produced.

Scour of a cohesive soil by submerged plane turbulent wall jets
 By K.A. Mazurek, N. Rajaratnam and D.C. Sego
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This paper presents the results of a laboratory study undertaken to examine the effect of hydraulic variables on the scour of a cohesive soil produced by submerged plane turbulent wall jets. The velocity and thickness of the jet were varied in tests with one cohesive soil in part to determine if repeatable scour experiments by these jets could be performed in cohesive material. Measurements were taken of the scour hole profiles at the asymptotic or equilibrium state of scour, including the maximum depth of scour, the location of the maximum scour depth, and the length of the scour hole.
Dimensional analysis is used to show that the scour hole dimensions at asymptotic state can be expressed as a function of the velocity at the nozzle, the density of the eroding fluid, the nozzle thickness, and the critical shear stress of the soil. The scour hole profiles are shown to scale with the maximum depth of scour and the distance from the nozzle where the scour is half the maximum scour depth. Observations of the growth of the scour holes are also presented.

Influence of additional inlet flow on the prerotation and performance of centrifugal impellers
 By Andrej Predin and Ignacijo Bilus¹
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In this paper we present the results of our experimental analysis regarding the influence of additional flow when added at the radial impeller entrance eye. This analysis was done on both operating and prerotation flow characteristics. The experimental system tested was arranged to operate using air. The additional flow adding system (AFAS) was placed at the entrance eye of the impeller through the guide system, which consists of the spiral volute at the entrance, ring guide pipe (where the guide vanes are placed), and a ring – like hollow at the end of the AFAS. The ring – like hollow was placed near the shroud at the entrance edge of the impeller blades. The guide vanes in the AFAS were placed in the axial direction, so that the added flow had no swirl component. The operating regime was tested, whereby the AFAS was filled by the flow under atmospheric pressure (non-forced loading). A good influence was evident on the operating characteristic. The stable operating range was enlarged and the operating noise decreased.
The achieved impeller head and the overall efficiency increased.

 

ISSUE 3

Fargue, founder of experimental river engineering
 Willi H. Hager
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The founder of experimental river engineering, the Frenchman Louis Fargue (1827–1910) conducted experiments in the last thirty years of the 19th century. His name – not being associated with any formula or any effect – is currently almost forgotten. The purpose of the present work is to highlight French hydraulics of the 19th century in general, and the contribution to its fame by Fargue in particular. His main papers are reviewed from present day knowledge after having given an overview of the environment in which he grew. These results are then discussed and a biography outlines the main stations of Fargue’s life.

 

An analysis of the variation of maximum flood stage of Lower Yangtze River
Chen Yin Chuan and Lu Hong Jun
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The study analyses the annual maximum flood stage of the Lower Yangtze River at Nanjing and the volume of runoff at Datong hydrologic station.
It shows that during the most recent twenty years the higher maximum flood stages occur more frequently and the mean annual maximum flood stage has increased. The peak and the short period volume of runoff at Datong station have become larger while the average volume of runoff of longer period has been almost constant. These phenomena are explained by the change of characteristics within the catchment of Lower and MiddleYangtze River due to human activity.

A new algorithm for a robust solution of the fully dynamic Saint–Venant equations
 Tullio Tucciarelli
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A new procedure for the numerical solution of the fully dynamic shallow water equations is presented. The procedure is a fractional step methodology where the original system is split into two sequential ones. The first system differs from the original one because of the head gradient term, that is treated as constant and equal to the value computed at the end of the previous time step. The solution of this system, called kinematic, is computed in each element using a spatial zero order approximation for both the heads and the flow rates by means of integration of single ODEs. The second system is called diffusive, contains in the momentum equations only the complementary terms and can be easily solved using implicit methods. The major advantages of the methodology are: (1) it guarantees mass conservation; (2) it shows unconditional stability with respect to the Courant number; (3) it can be applied to initially dry domains; (4) it can be applied to closed conduits without the help of the Preissman approximation.

 

Predictions of solute transport in a compound channel using turbulence models
 K. Shiono, C.F. Scott and D. Kearney
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Prediction of solute distributions in an asymmetric compound channel is carried out using two turbulence models. Results of the numerical models are compared with turbulence data recently obtained using laser Doppler anemometer (LDA) and laser induced fluorescence (LIF) in a small laboratory flume. The predicted distributions of solute and Reynolds flux using a k-• model and an algebraic stress model for various injection points near thewater surface are used to identify different mixing mechanisms. A skewed distribution of solute on the floodplain observed in the experimental data is well predicted by the algebraic stress model but not by the k-• model. The cause of the skewed distribution is examined through the variations of secondary flow and eddy diffusivity. The predicted eddy viscosity and diffusivity and the turbulent Schmidt number are discussed with the experimental data. As a result, solute concentration distribution can be well predicted by adjusting the turbulent Schmidt number even if the eddy viscosity was not correctly calculated by any particular model. An effect of secondary flow on peak concentration in the shear layer along the channel is also demonstrated.

The influence of roughness structure on flow resistance on steep slopes
 J. Aberle and G.M. Smart
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There is no standard flow resistance equation for the determination of mean flow velocity in mountain streams. The reason lies in the morphology of mountain streams, i.e. steep slopes, large roughness elements, bed forms and water depths of the same order of magnitude as the bed material size. Logarithmic, Froude and power-law approaches to determine flow resistance are discussed with respect to the roughness parameter which is usually a characteristic grain size. As a result of the irregular nature of gravel-bed profiles it is shown that the structure of these stream beds cannot be described sufficiently by a characteristic percentile of the grain size distribution. Statistical properties of a series of bed profiles are investigated in order to quantify the effect of roughness on flow resistance. The standard deviation of the bed elevations is introduced as characteristic roughness length and its applicability is verified by the analysis of experimental data. Based on this roughness parameter, an approach for the determination of flow resistance is derived which allows for spatial averaging of the flow field. Conclusions concerning the influence of bed forms on flow resistance are drawn with the use of the concept of the “at-a-site” hydraulic geometry.

Time evolution of scouring downstream of bed sills
 Roberto Gaudio and Andrea Marion
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Results of laboratory experiments conducted on time evolution of the scouring phenomenon at bed sills are presented. Starting from previous findings on long-term depth and length of the local scour hole downstream of bed sills, 12 long-duration tests were designed and performed in the Sloping Sediment Duct at HR Wallingford Ltd., using uniform sand. No sediment feeding system was adopted. Video-recordings of the scour holes through the glass-sided duct allowed successive image analysis to obtain water surface and bed profiles over time. Results confirmed the validity of the assessment method of the maximum scour depth, ys , at equilibrium; uncertainties arose about the length of the scour hole, ls . A cyclic phenomenon perturbing the scour hole was also observed and described. The investigation of the time evolution of ys showed that the scour hole develops rapidly and conditions close to equilibrium are achieved in a short time. The introduction of a morphological time, ts , permitted the non-dimensional description of the increasing of ys over time through a unique curve. The short- and the long-term local scour regions are clearly distinguished.An application of the results is shown in a numerical example.

The mean characteristics of horseshoe vortex at a cylindrical pier
M. Muzzammil and T. Gangadhariah
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The primary horseshoe vortex formed in front of a cylindrical pier and believed to be the prime agent responsible for scour has been investigated experimentally during the entire process of scouring. A simple and effective method was employed to obtain the time-averaged characteristics of the
vortex in terms of parameters relating variables of flow, pier and the channel bed. An expression for the maximum equilibrium scour depth has also been developed from the vortex velocity distribution inside scour hole. The resulting scour prediction equation has been found to give better results compared to the results of well-known predictor models when applied to model scour data.

A two-phase flow model of wave-induced sheet flow
 Tai-Wen Hsu, Hsien-Kuo Chang and Chih-Min Hsieh
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This paper presents a two-phase flow model that simulates the fluid and sediment motions in the sheet flow region under oscillatory conditions. Some major forcing terms such as the fluid/particle and particle/particle interactions and turbulent stresses are included in the model. By improving some assumptions of most existing models, the present model specifies the equivalent sand roughness and bed concentration as a function of the Shields parameter, which is variable with time and is physically more realistic over a mobile flat bed. A wave friction factor, which is governed by a new parameter, is obtained from the present model formulation. The present model is shown to provide a more accurate estimate of sediment concentrations than those models using a constant equivalent sand roughness. Numerical analyses also show that the suspended sediment retards the mean velocity and suppresses turbulence

Study of concentration fields in turbulent wake regions
Jiang Chun Bo, Du Li Hui and Liang Dong Fang
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The turbulent concentration fields in the wake of a circular cylinder were investigated by both numerical and experimental methods. Planar Laser- Induced Fluorescence (PLIF) techniquewas used to non-intrusively measure the simultaneous two-dimensional concentration fields, which is necessary for research on unsteady flows. The fractional step finite element formulation was extended to simulate the turbulent transportation processes in the wake region. This numerical formulation has third order accuracy and an enlarged stability domain which is suitable for convection dominated flows. The characteristics of the mean and instantaneous concentration distributions were analyzed in detail. The properties of the vortex movement and the concentration distributions were also analyzed. The numerical results were verified by the PLIF experiment.

Control of hydraulic jump by sill in triangular
Bachir Achour and Mahmoud Debabèche
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The control of an hydraulic jump by a thin wall continuous sill in a triangular channel with an aperture of 90• is analyzed experimentally.A relationship for the control of the hydraulic jump under any conditions of generation is presented in an adimensionnal form in order to have a general validity character. The sill effect on the stilling basin is observed and evaluated. This research has its application in the ditch irrigation with triangular shape, using the jump ability to raise the flow head plane downstream.