The following are abstracts from the Journal of Hydraulic Research, Volume 39, Issue 4
Towards the hydraulics of the hydroinformatics era
M. B. Abbott, V. M. Babovic and J. A. Cunge
Hydroinformatics is the study of the flows of knowledge and data related to the flow of water and all that it transports, together with interactions with both natural and man-made, or artificial, environments (Abbott, 1991). Hydraulics, understood as the study of flows of water, more recently extended to include the transport of matter in all its forms with these flows, is accordingly central to hydro-informatics. Without hydraulics, no hydroinformatics! From this situation it may at first appear as though hydroinformatics provides only a new periphery to hydraulics: a new way of transmitting hydraulics knowledge and data to society. In practice, however, the way in which hydraulics is viewed and practised is itself now changing as a result of its incorporation into the new paradigm that hydro-informatics provides. The first purpose of the present paper is to introduce some of the changes that are currently proceeding in hydraulics under the influence of developments occurring in hydroinformatics. The second purpose is to indicate the consequences of these changes for the application of hydraulics within society, and thus for the future direction of hydraulics and hydroinformatics themselves.
Hydraulics of simple habitat structures
H. Shamloo, N. Rajaratnam and C. Katopodis
Habitat structures are built in rivers to provide feeding and resting areas for fish. At the present time, only rough guidelines are available for the design of these structures. This paper presents the results of a laboratory study on the flow and erosion around simple habitat structures. Hemispheres with diameter D of 74 and 130 mm were placed on smooth, rough as well as erodible beds and Froude number of the approaching flow was in the range of 0.074 to 0.6. The relative depth d/h where d is the depth of and h is the height of the body was found to be the important parameter and was varied from about 0.6 to 4.3. Four different regimes of flow were found, which were classified based on the relative depth. Downstream of the body, there was a recirculation region (closed wake) with a length of about 2D which was followed by an open turbulent wake. The structure of flow in this open wake was analysed in two layers using the concept of the wall wake. In the plane of symmetry, the inner layer was analysed using the law of the wall whereas the outer layer was analysed using the wake equation of Schlichting. The variation of the velocity in the transverse direction was also analysed using the concept of similar profiles. Further an empirical correlation was found for the velocity scale. The amplification of the bed shear stress near the body, especially for the rough bed was significant. Some observations were also made on the nature of erosion around the hemisphere placed on erodible beds of two sand sizes of 1.11 and 2.1 mm. It was found that the pattern of erosion was different for the different flow regimes. The maximum equilibrium clear water scour depth occurred in front of hemispherical bodies and was approximately equal to 0.67 D.
Scour around spur dikes and bridge abutments
U. C. Kothyari and K. G. Ranga Raju
Realistic estimation of scour depth around spur dikes and bridge abutments in alluvial rivers is important for safe and economic design of their foundations. Procedures have been developed by previous investigators for determination of design scour depth in steady flows at abutments and spur dikes by making use of the design discharge. However, the time required by the design discharge to scour to its full potential is generally much larger than the time for which it runs. Therefore, computations on temporal variation of scour depth are also important for design purposes. Scour processes at bridge piers, abutments and spur dikes have been found to be similar except that the boundary layer effect induced by the channel wall upstream of the abutment or spur dike causes less scour around these as compared to the case of piers. In the present study, therefore, the concept of an analogous pier is developed. The analogous pier would have the same equilibrium scour depth as the given abutment or spur dike under similar hydraulic conditions. The parameters relating to drag due to flow around abutment/ spur dike and bridge pier have been found to be useful in establishing a relationship for the diameter of the analogous pier. The temporal variation of scour depth and the equilibrium scour depth at the spur dike and the abutment are then computed using pier scour equations with size of the analogous pier being taken as the pier diameter. Results obtained are verified using laboratory data of several investigators for both clear-water and live-bed scour conditions.
Effect of downstream control on stability and mixing of a vertical plane buoyant jet in confined depth
C. P. Kuang and Joseph H. W. Lee
The effect of downstream control on the mixing of a plane turbulent heated jet discharging vertically into confined depth is studied using the buoyancy extended 
model. The steady two-dimensional turbulent flow, temperature and turbulence fields are computed using the finite volume method on a high resolution grid. In the absence of a specific downstream control, the numerical predictions demonstrate three generic flow patterns for different jet discharges and environmental parameters: i) a flow with circulation cells of alternate rotation for non-buoyant discharge; ii) a stable buoyant discharge with the mixed fluid leaving the vertical jet region in a surface warm water layer; and iii) an unstable buoyant discharge with flow recirculation and re-entrainment of heated water. A stratified counterflow region always appears in the far-field for both stable and unstable buoyant discharges. The near field interaction and hence discharge stability is governed by only two dimensionless parameters. The discharge densimetric Froude number Fo and the depth to jet width ratio H/B. The computed velocity and temperature fields agree well with the laboratory flow-visualization and temperature measurements of Jirka & Harleman (1979). Numerical prediction of stability categories is in excellent agreement with experiments. For a given discharge and depth, it is found that the jet stability can be predicted regardless of downstream control, provided that the channel length exceeds about 6H. The effect of a strong downstream control close to the discharge primarily results in a flooded internal jump and the lowering of the interface level in the stratified counterflow region. Consistent with the detailed measurements of Andreo-poulos, Praturi and Rodi (1986), the predictions show a clear reduction of the bulk dilution, although the effect of downstream control on the jet discharge stability is insignificant.
An implicit scheme for steady two-dimensional free-surface flow calculation
Athanasios J. Klonidis and Johannes V. Soulis
An implicit numerical scheme has been developed and subsequently applied to calculate steady, two-dimensional depth averaged, free-surface flow problems. The implicit form of the scheme gives fast convergence. The scheme is second order accurate and unconditionally stable. The free-surface flow equations are transformed into a non-orthogonal, boundary-fitted coordinate system so as to simulate with accuracy irregular geometries. The model is used to analyse a wide variety of hydraulic engineering problems including subcritical flow in a converging-diverging flume, supercritical flow at a channel expansion with various Froude numbers, and mixed sub- and supercritical flow in a converging channel. The computed results are compared with measurements as well as with other numerical solutions and satisfactory agreement is achieved.
3D layered-integrated modelling of mass exchange in semi-enclosed water bodies
C. W. Li and J. Gu
The flow patterns in semi-enclosed water bodies are generally complicated and have significant effect on the water quality and fluid exchange there. The exchange of of fluid between the semi-enclosed water body and outside is due to two physical mechanisms. The first is the flushing due to tidal effect. The second is the shear induced by the velocity difference between the flow within the water body and outside. To predict the flow and solute transport in these water bodies a three-dimensional layer-integrated numerical model has been developed. To account for the turbulence which consists of the free shear component and the bottom friction component the k−fà model is employed. The numerical model has been applied to the cases of tidal flow as well as steady river flow outside a rectangular harbour with or without breakwater. Compared with the available experimental results, the gross mass exchange both due to tidal effect and shear can be estimated satisfactorily by the numerical model.
Adaptive quadtree model of shallow-flow hydrodynamics
A.G.L. Borthwick, S. Cruz León and J. Józsa
Natural shallow-flow domains have irregular boundaries which can strongly influence the interior flow field. Here, the nonlinear shallow water equations are solved on adaptive quad-tree grids that can approximate any two-dimensional boundary topology and are easy to enrich or coarsen. A special indexing system matches the quadtree structure to conventional finite volume notation. Grid adaptation is controlled by a cell circulation parameter. Simulations of standard test flows are in close agreement with analytical and other numerical data. The sample application of wind-induced circulation in Lake Balaton, Hungary, demonstrates the ability of the model to deal with a complicated shallow-flow geometry.
An example of computational approach used for aerodynamic design of a rain disdrometer
Emad Habib and Witold F. Krajewski
The present work reports on the application of a computational fluid dynamics-based method as a tool to improve the aerodynamic design of rainfall measurement devices. The focus is on a new instrument, a two-dimensional video disdrometer that provides information about raindrop size distribution. The distorted wind field around and inside the instrument's body is simulated using a three-dimensional numerical model. A modified geometry of the instrument, suggested for operational purposes, is tested numerically. Trajectories of raindrops are simulated to investigate the wind effect on the catchment efficiency of the instrument. A stochastic Lagrangian particle-tracking model that accounts for the turbulence effect is examined. General guidelines related to aerodynamic aspects of the design of in situ rainfall measuring devices are discussed.
Dynamic orifice model on waterhammer analysis of high or medium heads of small hydropower schemes
H. Ramos and A. B. Almeida
The most severe hydropower transients are induced in long hydraulic circuits due to extreme operating conditions. A computational model was developed in order to on one hand ensure waterhammer system control and, on the other hand, provide a more reliable and easier analysis for different specific speed turbines and alternative solutions of the system as a whole, through interaction between different hydraulic components. In reaction turbines, runaway conditions and guide vane closure cause significant discharge variations and pressure fluctuations that can affect the design of conveyance systems. A new approach for groups modelling as dynamic orifices concept was developed enabling the characterisation of the integrated system. The simulation results were compared with laboratory tests. This model can be used in the initial stages of civil works design as an efficient way to better characterise the hydrodynamic behaviour of the system when equipped with reaction turbines.
Numerical simulation and prevention of water freezing in outdoor penstocks
loan Sârbu and Francisc Kalmar
Pipes laid in open air and conveying water can freeze in winter times. A blockage due to freezing can be effectively prevented by providing a minimum discharge. This precaution ensures the free flow of water through the pipe, but does not stop the forming of an ice layer on the inner pipe wall. In this paper a mathematical model is developed to determine minimal protection discharge and simulation of variation in time along the pipe of ice layer formed inside outdoor pipes during non-stationary atmospheric regime. The model allows the study of the pipe capacity to transport the normal discharge in operation and minimal protection discharge without affecting the hydraulic characteristics of the flow. Also, it gives the possibility to adopt economical solutions for the problem of protecting these pipes from frost. The performance of the developed model is illustrated using a numerical example.
