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Diabetologia Notes de lecture     Hybrid Journal  
Diabetology Intl.     Hybrid Journal   (Followers: 1, SJR: 0.273, h-index: 5)
Dialectical Anthropology     Hybrid Journal   (Followers: 9, SJR: 0.314, h-index: 9)
Die Weltwirtschaft     Hybrid Journal   (Followers: 2)
Differential Equations     Hybrid Journal   (Followers: 2, SJR: 0.364, h-index: 15)
Differential Equations and Dynamical Systems     Hybrid Journal   (Followers: 1, SJR: 0.63, h-index: 7)
Digestive Diseases and Sciences     Hybrid Journal   (Followers: 4, SJR: 1.19, h-index: 89)
Directieve therapie     Hybrid Journal  
Discrete & Computational Geometry     Hybrid Journal   (Followers: 3, SJR: 1.269, h-index: 40)
Discrete Event Dynamic Systems     Hybrid Journal   (Followers: 3, SJR: 0.42, h-index: 32)
Distributed and Parallel Databases     Hybrid Journal   (Followers: 4, SJR: 0.766, h-index: 30)
Distributed Computing     Hybrid Journal   (Followers: 2, SJR: 1.41, h-index: 31)
DNP - Der Neurologe und Psychiater     Full-text available via subscription  
Documenta Ophthalmologica     Hybrid Journal   (Followers: 2, SJR: 0.946, h-index: 40)
Doklady Biochemistry and Biophysics     Hybrid Journal   (Followers: 2, SJR: 0.2, h-index: 10)
Doklady Biological Sciences     Hybrid Journal   (SJR: 0.248, h-index: 10)
Doklady Botanical Sciences     Hybrid Journal  
Doklady Chemistry     Hybrid Journal   (SJR: 0.272, h-index: 12)
Doklady Earth Sciences     Hybrid Journal   (SJR: 0.48, h-index: 17)
Doklady Mathematics     Hybrid Journal   (SJR: 0.345, h-index: 13)
Doklady Physical Chemistry     Hybrid Journal   (SJR: 0.299, h-index: 12)
Doklady Physics     Hybrid Journal   (Followers: 1, SJR: 0.293, h-index: 17)
Douleur et Analg├ęsie     Hybrid Journal   (SJR: 0.113, h-index: 6)
Drug Delivery and Translational Research     Hybrid Journal   (Followers: 2, SJR: 0.607, h-index: 8)
Drug Safety - Case Reports     Open Access   (Followers: 1)
Drugs : Real World Outcomes     Hybrid Journal   (Followers: 2)
Dynamic Games and Applications     Hybrid Journal   (Followers: 2, SJR: 0.481, h-index: 5)
Dysphagia     Hybrid Journal   (Followers: 87, SJR: 0.822, h-index: 52)
e & i Elektrotechnik und Informationstechnik     Hybrid Journal   (Followers: 9, SJR: 0.279, h-index: 9)
e-Neuroforum     Hybrid Journal  
Early Childhood Education J.     Hybrid Journal   (Followers: 13, SJR: 0.466, h-index: 16)
Earth Science Informatics     Hybrid Journal   (Followers: 3, SJR: 0.282, h-index: 7)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 7, SJR: 0.303, h-index: 29)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 7, SJR: 0.482, h-index: 21)
Earthquake Science     Hybrid Journal   (Followers: 8, SJR: 0.418, h-index: 9)
East Asia     Hybrid Journal   (Followers: 8, SJR: 0.18, h-index: 9)
Eating and Weight Disorders - Studies on Anorexia, Bulimia and Obesity     Hybrid Journal   (Followers: 13, SJR: 0.362, h-index: 27)
EcoHealth     Hybrid Journal   (Followers: 3, SJR: 0.88, h-index: 26)
Ecological Research     Hybrid Journal   (Followers: 8, SJR: 0.847, h-index: 43)
Economia e Politica Industriale     Hybrid Journal  
Economia Politica     Hybrid Journal   (SJR: 0.375, h-index: 6)
Economic Botany     Hybrid Journal   (Followers: 8, SJR: 0.527, h-index: 44)
Economic Bulletin     Hybrid Journal   (Followers: 4)
Economic Change and Restructuring     Hybrid Journal   (SJR: 0.264, h-index: 9)
Economic Theory     Hybrid Journal   (Followers: 16, SJR: 2.557, h-index: 34)
Economic Theory Bulletin     Hybrid Journal   (Followers: 2)
Economics of Governance     Hybrid Journal   (Followers: 2, SJR: 0.408, h-index: 14)
Ecosystems     Hybrid Journal   (Followers: 23, SJR: 1.909, h-index: 93)
Ecotoxicology     Hybrid Journal   (Followers: 9, SJR: 1.333, h-index: 56)
Education and Information Technologies     Hybrid Journal   (Followers: 74, SJR: 0.366, h-index: 16)
Educational Assessment, Evaluation and Accountability     Hybrid Journal   (Followers: 17, SJR: 0.374, h-index: 15)
Educational Psychology Review     Hybrid Journal   (Followers: 20, SJR: 2.776, h-index: 61)
Educational Research for Policy and Practice     Hybrid Journal   (Followers: 8, SJR: 0.273, h-index: 9)
Educational Studies in Mathematics     Hybrid Journal   (Followers: 14, SJR: 0.825, h-index: 32)
Educational Technology Research and Development     Partially Free   (Followers: 62, SJR: 1.785, h-index: 52)
Electrical Engineering     Hybrid Journal   (Followers: 16, SJR: 0.336, h-index: 18)
Electrocatalysis     Hybrid Journal   (SJR: 0.883, h-index: 10)
Electronic Commerce Research     Hybrid Journal   (Followers: 3, SJR: 0.582, h-index: 16)
Electronic Markets     Hybrid Journal   (Followers: 5, SJR: 0.411, h-index: 8)
Electronic Materials Letters     Hybrid Journal   (Followers: 3, SJR: 1.407, h-index: 15)
Elemente der Mathematik     Hybrid Journal   (Followers: 1)
Emergency Radiology     Hybrid Journal   (Followers: 5, SJR: 0.678, h-index: 25)
Emission Control Science and Technology     Hybrid Journal   (Followers: 1)
Empirica     Hybrid Journal   (Followers: 3, SJR: 0.319, h-index: 16)
Empirical Economics     Hybrid Journal   (Followers: 8, SJR: 0.489, h-index: 31)
Empirical Software Engineering     Hybrid Journal   (Followers: 7, SJR: 1.285, h-index: 39)
Employee Responsibilities and Rights J.     Hybrid Journal   (Followers: 3, SJR: 0.361, h-index: 15)
Endocrine     Hybrid Journal   (Followers: 7, SJR: 0.878, h-index: 57)
Endocrine Pathology     Hybrid Journal   (Followers: 2, SJR: 0.638, h-index: 31)
Energy Efficiency     Hybrid Journal   (Followers: 14, SJR: 0.732, h-index: 14)
Energy Systems     Hybrid Journal   (Followers: 14, SJR: 1.176, h-index: 7)
Engineering With Computers     Hybrid Journal   (Followers: 5, SJR: 0.433, h-index: 30)
Entomological Review     Hybrid Journal   (Followers: 7, SJR: 0.144, h-index: 5)
Environment Systems & Decisions     Hybrid Journal   (Followers: 2)
Environment, Development and Sustainability     Hybrid Journal   (Followers: 32, SJR: 0.419, h-index: 29)
Environmental and Ecological Statistics     Hybrid Journal   (Followers: 6, SJR: 0.458, h-index: 32)
Environmental and Resource Economics     Hybrid Journal   (Followers: 18, SJR: 1.632, h-index: 54)
Environmental Biology of Fishes     Hybrid Journal   (Followers: 5, SJR: 0.725, h-index: 58)
Environmental Chemistry Letters     Hybrid Journal   (Followers: 2, SJR: 0.741, h-index: 28)
Environmental Earth Sciences     Hybrid Journal   (Followers: 12, SJR: 0.724, h-index: 63)
Environmental Economics and Policy Studies     Hybrid Journal   (Followers: 5, SJR: 0.524, h-index: 4)
Environmental Evidence     Open Access   (Followers: 1)
Environmental Fluid Mechanics     Hybrid Journal   (Followers: 3, SJR: 0.437, h-index: 24)
Environmental Geochemistry and Health     Hybrid Journal   (Followers: 3, SJR: 1.013, h-index: 36)
Environmental Geology     Hybrid Journal   (Followers: 11)
Environmental Health and Preventive Medicine     Hybrid Journal   (Followers: 3, SJR: 0.522, h-index: 19)
Environmental Management     Hybrid Journal   (Followers: 38, SJR: 0.942, h-index: 66)
Environmental Modeling & Assessment     Hybrid Journal   (Followers: 11, SJR: 0.533, h-index: 31)
Environmental Monitoring and Assessment     Hybrid Journal   (Followers: 23, SJR: 0.685, h-index: 52)
Environmental Science and Pollution Research     Hybrid Journal   (Followers: 14, SJR: 0.885, h-index: 46)
Epileptic Disorders     Hybrid Journal   (SJR: 0.608, h-index: 38)
EPJ A - Hadrons and Nuclei     Hybrid Journal   (Followers: 1, SJR: 1.287, h-index: 63)
EPJ B - Condensed Matter and Complex Systems     Hybrid Journal   (Followers: 2, SJR: 0.731, h-index: 89)
EPJ direct     Hybrid Journal  
EPJ E - Soft Matter and Biological Physics     Hybrid Journal   (Followers: 1, SJR: 0.641, h-index: 62)
EPMA J.     Open Access   (SJR: 0.284, h-index: 6)
ERA-Forum     Hybrid Journal   (Followers: 4, SJR: 0.128, h-index: 3)
Erkenntnis     Hybrid Journal   (Followers: 15, SJR: 0.621, h-index: 16)
Erwerbs-Obstbau     Hybrid Journal   (SJR: 0.206, h-index: 9)
Esophagus     Hybrid Journal   (SJR: 0.311, h-index: 10)

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Journal Cover Environmental Fluid Mechanics
  [SJR: 0.437]   [H-I: 24]   [3 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1573-1510 - ISSN (Online) 1567-7419
   Published by Springer-Verlag Homepage  [2280 journals]
  • Measurements of sediment pickup rate over dune-covered bed
    • Abstract: Abstract Laboratory experiments were conducted to measure sediment pickup rate over two-dimensional fixed dunes. Measurements were performed over both stoss and lee sides of the dune with sediments of D 50 = 0.23, 0.44 and 0.86 mm. Flow velocity and turbulence were also measured by using an acoustic Doppler velocimeter. By analysing the experimental data, an empirical sediment pickup function based on depth-averaged flow parameters was proposed to estimate the pickup rate over the dune.
      PubDate: 2016-02-01
  • Twin inclined jets in crossflow: experimental investigation of different
           flow regimes and jet elevations
    • Abstract: Abstract The present experimental study is dedicated to unfolding the mixing process generated by double-inclined, variably elevated jets in crossflow. Twin tandem jets in crossflow are very common in the industry and are closely dependent on several parameters. Detailing the induced interactions in such a model would ultimately enhance our understanding and help optimize related applications. The jets handled in the present work are placed three diameters apart, arranged in line with the oncoming crossflow and sent at variable levels (h = 0, 1, 2, 5 cm) from the ground of a wind tunnel and are discharged from elliptic discharging cross sections. Elliptic jets are of particular interest in applications like industrial and boat chimneys, and are practically easily obtained by razing circular cylinders at the desired inclination and height. Particle image velocimetry and coupled charge device CCD camera were used. The dynamic and turbulent behavior of the resulting flowfield was characterized in terms of streamlines, velocity components and vortical structures. The obtained data helped highlight the impact of jets’ elevation over their mixing mechanism among the surrounding free stream: establishment of the resulting flowfield dynamics and settlement of the induced vortical structures. The mixing process evolution was also considered under different flow regimes. For the matter an injection ratio (defined as jets to the mainstream’s velocity ratio) raging between 0.67, 1 and 1.29 was considered. These cases correspond to jets dynamically dominated by, equivalent to or more dominant than the mainstream. The impact of jets’ elevation combined to that of the injection ratio affects both the developed vortical structures and the established dynamic fields, which in turn highly affects the induced mixing process.
      PubDate: 2016-02-01
  • RANS simulation of neutral atmospheric boundary layer flows over complex
           terrain by proper imposition of boundary conditions and modification on
           the k - ε model
    • Abstract: Abstract In this study, a modelling methodology is proposed for RANS simulations of neutral Atmospheric Boundary Layer (ABL) flows on the basis of the standard k-ε model, which allows the adoption of an arbitrary shear stress model. This modelling methodology is first examined in the context of an open flat terrain in an empty domain to ascertain there are no substantial changes in the prescribed profiles. The results show that relatively good homogeneity can be achieved with this modelling methodology for various sets of inflow boundary profiles. In addition, to extend the solutions derived from the standard k-ε model to RNG k-ε model, the RNG k-ε model is in detail assembly and tuned. Finally, the topographic effects on surface wind speeds over a complex terrain are assessed with the combined use of the proposed methodology and the modified RNG model. The numerical results are in good agreement with wind tunnel testing results and long-term field observations. A discussion of the effects of horizontal homogeneity and turbulence models on the simulated wind flows over a complex terrain is also given.
      PubDate: 2016-02-01
  • Large eddy simulations of 45° inclined dense jets
    • Abstract: Abstract Submerged inclined dense jets (negatively buoyant jets) occur in many engineering applications such as brine discharges from seawater desalination plants and de-cooling water discharges from liquefied natural gas plants, and their mixing behavior needs to be examined in details for the environmental impact analysis. In the present study, a detailed numerical investigation was performed using the large eddy simulation (LES) approach with both the Smagorinsky and Dynamic Smagorinsky sub-grid scale (SGS) models to simulate the characteristics of the inclined dense jet with 45° inclination. The numerical predictions included the jet trajectory, geometrical characteristics, jet spread and eddy structures. Experimental measurements were also obtained for the validation of the LES predictions, and data from existing studies in the literature were included for comparison. Overall, the LES predictions were able to reproduce the geometric characteristics of the inclined dense jet in a satisfactory manner in most aspects. The dilution was however generally underestimated, which was attributed primarily to the inability of the SGS models to reproduce the convective mixing induced by the buoyancy-induced instability using the adopted grid spacing in the bottom half of the inclined dense jet.
      PubDate: 2016-02-01
  • Computation of the Basset force: recent advances and environmental flow
    • Abstract: Abstract When numerically integrating the equation describing the motion of a particle in a carrier fluid, the computation of the Basset (history) force becomes by far the most expensive and cumbersome, as opposed to forces such as drag, virtual mass, lift, buoyancy and Magnus. The expression representing the Basset force constitutes an integro-differential term whose standard integrand is singular when the upper integration limit is enforced. These shortcomings have led some researchers to either disregard or outright neglect the contribution of the Basset force to the total force, even in those cases where it may yield to important errors in the determination of particle trajectories in the computation of sediment transport and other environmental flows. This work is devoted to review four recent contributions associated with the computation of the Basset force, and to compare their proposals to diminish the inherent problems of the term integration. All papers, except one, use variants of a window-based approach; the most recent contribution, in turn, employs a specialized quadrature to increase the accuracy of the computation. An analysis was carried out to compare CPU computation times, rates of convergence and accuracy of the approximations versus a known analytical solution. All methods provide sound solutions to the issues associated with the computation of the Basset force; further, a road map to select the best solution for each given problem is provided. Finally, we discuss the implications of the techniques for the simulation of sediment transport processes and other environmental flows.
      PubDate: 2016-02-01
  • Modeling investigation of asymmetric tidal mixing and residual circulation
           in a partially stratified estuary
    • Abstract: Abstract A three-dimensional hydrodynamic model was applied to the Danshuei River estuarine system in northern Taiwan to investigate the influence of flood-ebb, spring-neap tidal cycles, and salinity distribution on tidal mixing, residual circulation, stratification, and tidal asymmetry. The model was validated using observational data collected in 2008. The results from the model agreed well with observations of water surface elevation, tidal currents, and salinity. It was found that the depth-averaged tidal current during flood tide is weaker with a shorter duration than that during ebb tide in the estuary, which was attributed to tidal asymmetry. Vertical profiles of salinity, flow, eddy diffusivity, and Richardson number also showed a marked asymmetry between flood and ebb tides. Bottom boundary stresses were higher during flood tides than during ebb tides, resulting in more mixing occurrence and consequently decreasing the Richardson numbers. The tidally averaged salinity was more stratified during neap tides than during spring tides because the presence of the stronger vertical diffusivity and turbulent kinetic energy during spring tides. The modeling results also confirmed that the residual circulation was stronger during neap tides than during spring tides.
      PubDate: 2016-02-01
  • SPH numerical investigation of the velocity field and vorticity generation
           within a hydrofoil-induced spilling breaker
    • Abstract: Abstract In the present work, the velocity field and the vorticity generation in the spilling generated by a NACA 0024 hydrofoil were studied. SPH simulations were obtained by a pseudo-compressible XSPH scheme with pressure smoothing; both an algebraic mixing-length model and a two-equation model were used to represent turbulent stresses. Given the key role of vortical motions in the generation of the spilling breaker, the sources of vorticity were then examined in detail to confirm the interpretation of the mean flow vortical dynamics given in a paper by Dabiri and Gharib (J Fluid Mech 330: 113–139, [1997]). The high precision of the SPH model is confirmed through a comparison with experimental data. Experimental investigations were carried out by measuring the velocity field with a backscatter, two-component four-beam optic-fiber LDA system. The agreement between the numerical results and laboratory measurements in the wake region is satisfactory and allows the evaluation of the wave breaking efficiency of the device by a detailed analysis of the simulated flow field.
      PubDate: 2016-02-01
  • Hydrodynamics of suspended canopies with limited length and width
    • Abstract: Abstract Experimental measurements and numerical simulations are carried out to determine the hydrodynamics induced by suspended canopies of limited width and height for canopies with six different densities and canopy element arrangements and two different upstream velocities. Measurements of velocity are obtained using acoustic Doppler velocimetry and the drag force via a load cell. Numerical simulation results using OpenFOAM agree very well with the experimental data and are used to investigate the generated flow fields in detail. The bulk features of the flow are similar to those of other canopies, including emergent and submerged canopies, but the finite dimensions of the canopy results in flow patterns that differ from suspended canopies of essentially infinite width. The detailed hydrodynamics of the flow are controlled by the blockage of the suspended canopy which depends both on the canopy density and the lateral spacing between consecutive longitudinal rows of canopy elements. Increased flow blockage results in increases in the drag coefficient from 0.72 to 1.4, reduction in the flow rate inside the canopy from 58 to 98 % (of the diverted flow, 20–43 % is diverted below the canopy) and increases in the steady wake zone length from 0.6 to 4 times the canopy length. Flow blockage has relatively little effect on the length of the upstream adjustment and total wake zones at 1.09 and 7 times the canopy length respectively. The flow also depends only weakly on the upstream velocity.
      PubDate: 2016-02-01
  • Advent of sheet flow in suction affected alluvial channels
    • Abstract: Abstract The presence of suction (flow of water from channel to ground water) affects the channel hydrodynamics and increases the bed shear stress. At high bed shear stress in alluvial channels made of the non-cohesive material, sediment transport occurs as sheet flow layer of high sediment concentration. The sediment transport in the form of sheet flow has been observed in the present study when suction was applied to the non-transporting channels designed on incipient motion condition. The erosion of the channel banks contributed to the sheet flow because of the increased channel bed shear stress. An empirical relation for the thickness of sheet flow layer has been developed which includes suction as independent parameter along with others.
      PubDate: 2016-02-01
  • A recycling method for the large-eddy simulation of plumes in the
           atmospheric boundary layer
    • Abstract: Abstract A method for the large-eddy simulation (LES) of dispersion and mixing of passive scalars is developed and evaluated. The new method addresses the requirements of tracking the evolution of plumes for large distances from their sources while attaining a low computational cost. To reduce computational cost, the velocity and thermodynamic fields are solved on a doubly periodic domain in the horizontal directions. In contrast, when the plume reaches the downstream end of the computational domain, it is reintroduced at the upstream plane but as a different scalar field. The same procedure is repeated when the new scalar field reaches the downstream boundary. By using several scalar fields to describe the evolution of a single plume, the simulation is computationally cheaper since the same velocity and thermodynamic fields are reused, or recycled, when computing the plume evolution. The recycling method is verified by showing that low-order plume statistics are identical to a single-domain LES. Three cases of dispersion and mixing from a point ground source in diverse boundary layer conditions (stable, convectively unstable, and shallow cumulus convection) are considered. Moreover, the LES results are compared with the predictions a Gaussian plume model, which is found to perform satisfactorily in all cases when accurate information about the state of the boundary layer is provided.
      PubDate: 2016-02-01
  • Resistance and reconfiguration of natural flexible submerged vegetation in
           hydrodynamic river modelling
    • Abstract: Abstract In-stream submerged macrophytes have a complex morphology and several species are not rigid, but are flexible and reconfigure along with the major flow direction to avoid potential damage at high stream velocities. However, in numerical hydrodynamic models, they are often simplified to rigid sticks. In this study hydraulic resistance of vegetation is represented by an adapted bottom friction coefficient and is calculated using an existing two layer formulation for which the input parameters were adjusted to account for (i) the temporary reconfiguration based on an empirical relationship between deflected vegetation height and upstream depth-averaged velocity, and (ii) the complex morphology of natural, flexible, submerged macrophytes. The main advantage of this approach is that it removes the need for calibration of the vegetation resistance coefficient. The calculated hydraulic roughness is an input of the hydrodynamic model Telemac 2D, this model simulates depth-averaged stream velocities in and around individual vegetation patches. Firstly, the model was successfully validated against observed data of a laboratory flume experiment with three macrophyte species at three discharges. Secondly, the effect of reconfiguration was tested by modelling an in situ field flume experiment with, and without, the inclusion of macrophyte reconfiguration. The inclusion of reconfiguration decreased the calculated hydraulic roughness which resulted in smaller spatial variations of simulated stream velocities, as compared to the model scenario without macrophyte reconfiguration. We discuss that including macrophyte reconfiguration in numerical models input, can have significant and extensive effects on the model results of hydrodynamic variables and associated ecological and geomorphological parameters.
      PubDate: 2016-02-01
  • Definition of mixing zones in rivers
    • Abstract: Abstract The adequate definition of the mixing zone generated by the discharge of an effluent is of great importance, as it serves as support for the environmental authorities on the decision-making about the authorization of the discharge. The evolution of the mixing zone of an effluent is affected by different kind of phenomena as temporal variations on the hydrodynamic conditions, spatial variations in the geomorphology and bathymetry of the receiving water, etc. The correct definition of the mixing zone should take into account these factors, for which the use of mathematical modelling is needed. The turbulent hydrodynamic processes in the near field of the discharge and in the far field occur at different spatial and temporal scales. The mathematical model needs to be able of simulating the hydrodynamic and transport processes on both fields. The present paper proposes a methodology to be followed when the prediction of the extents of the mixing zone generated by an effluent discharged into a river is needed. The methodology consists of the obtaining of the necessary hydrodynamic and pollutant concentration data on the effluent and on the receiving water; the building of the adequate calculation meshes for the modelling; the calibration and validation of the model; and finally the definition of the critical conditions for the prediction of the behaviour of the mixing zone. An example of application of the proposed methodology is shown for a real case, the discharge of the WWTP of Casar de Periedo town in the Saja River, Cantabria, Spain, for which field data have been measured. The prediction of the extents of the mixing zone for this case was made using a hydrodynamic two-dimensional depth-averaged long wave model jointly with a transport model. In order to simulate the near field and the far field jointly, an Embedded mesh system was built. For the Embedded mesh system, it was needed the establishment of conditions for the information exchange between the meshes.
      PubDate: 2016-02-01
  • Rapid operation of a Tainter gate: generation process and initial upstream
           surge motion
    • Abstract: Abstract In water supply channels, the brusque operation of control gates may induce large unsteady flow motion called surges. Such a rapid operation of gates must often be restricted, although it may be conducted to scour silted channels and sewers. Herein a physical study was conducted under controlled flow conditions to study the turbulent mixing in the very-close vicinity of a rapidly opening/closing Tainter gate, with a focus on the unsteady transient mixing induced by the gate operation. The data suggested that the negative/positive surge generation was associated with large instantaneous free-surface fluctuations. The velocity measurements indicated significant variations in longitudinal velocity during the surge generation, as well as large fluctuations of all velocity components. The processes were associated with large Reynolds stress levels. A succession of rapid closure and opening of undershoot gates provided optimum conditions to scour silted canals, and the present results gave some detailed insights into the physical processes.
      PubDate: 2016-02-01
  • Study of flow formed by three coplanar impinging pipe jets at inclination
           angles of 30° and 45°
    • Abstract: Abstract This paper presents an experimental study of the interactions of three fully-submerged, coplanar impinging jets issued from long pipes. The jets were neutrally buoyant and were arranged symmetrically about the axis of a central jet, with two side jets set to intersect with the central jet at two inclination angles (30° and 45°) and three Reynolds numbers (4240, 6400 and 8000). Measurements of the flow fields were performed using particle image velocimetry to examine the flow structures in various planes, i.e., the jet axis plane (X–Y), the jet normal plane (X–Z) and the cross-sectional plane (Y–Z). This flow configuration results in pronounced interactions among the three jets, and hence better mixing than that of a canonical single pipe jet as illustrated by augmented centreline velocity decay, spreading rate and turbulence level. The jets at the inclination angle of 45° impinge and mix more rapidly than those at 30°. For each case, the flow is highly 3-dimensional, and jet development displayed several distinct regions (converging, merging and combining) along the streamwise direction. The expansion of flow in the X–Y plane is similar to the shape of a hyperbola with necking formed immediately downstream of the impinging point, whereas that in the X–Z plane assumes the shape of a parabola with an open rim exhibiting a pronounced velocity deficit in the central part of the combining flow. Self-similarity of streamwise mean velocity is explored in the combining region of the flow on the two planes of symmetry (X–Y and X–Z). Flow development in the combining region is dominated by large-scale vortical structures, including von Kárman-like spanwise vortices in the X–Y plane and secondary circulation in the form of two pairs of counter-rotating streamwise vortices in the Y–Z plane.
      PubDate: 2016-01-22
  • Embedded large eddy simulation approach for pollutant dispersion around a
           model building in atmospheric boundary layer
    • Abstract: Abstract In the present article, the potential of embedded large eddy simulation (ELES) approach to reliably predict pollutant dispersion around a model building in atmospheric boundary layer is assessed. The performance of ELES in comparison with large eddy simulation (LES) is evaluated in several ways. These include a number of qualitative and quantitative comparisons of time-averaged and instantaneous results with wind tunnel measurements supplemented by statistical data analyses using scatter plots and standard evaluation metrics. Results obtained by both LES and ELES approaches show very good agreement with the experiment. However, addition of turbulence to mean flow at Reynolds averaged Navier–Stokes (RANS)–LES interface in ELES approach not only increases the turbulence intensity, it also results in larger values of turbulent kinetic energy (TKE) as well as a shorter reattachment length in the wake region. Accordingly, higher levels of TKE predicted by ELES increase the local intensity of concentration leading to shorter plume shapes as compared with LES. In general, ELES shows better agreement with experiment on the surfaces of model building and also in the downstream wake region. In terms of computational costs, the CPU time required to obtain statistical values in ELES is about 49 % lower than that of LES and the number of iterations per time step is also reduced by 55 % as compared with LES.
      PubDate: 2016-01-13
  • Simulations of the flow in the Mahakam river–lake–delta
           system, Indonesia
    • Abstract: Abstract Large rivers often present a river–lake–delta system, with a wide range of temporal and spatial scales of the flow due to the combined effects of human activities and various natural factors, e.g., river discharge, tides, climatic variability, droughts, floods. Numerical models that allow for simulating the flow in these river–lake–delta systems are essential to study them and predict their evolution under the impact of various forcings. This is because they provide information that cannot be easily measured with sufficient temporal and spatial detail. In this study, we combine one-dimensional sectional-averaged (1D) and two-dimensional depth-averaged (2D) models, in the framework of the finite element model SLIM, to simulate the flow in the Mahakam river–lake–delta system (Indonesia). The 1D model representing the Mahakam River and four tributaries is coupled to the 2D unstructured mesh model implemented on the Mahakam Delta, the adjacent Makassar Strait, and three lakes in the central part of the river catchment. Using observations of water elevation at five stations, the bottom friction for river and tributaries, lakes, delta, and adjacent coastal zone is calibrated. Next, the model is validated using another period of observations of water elevation, flow velocity, and water discharge at various stations. Several criteria are implemented to assess the quality of the simulations, and a good agreement between simulations and observations is achieved in both calibration and validation stages. Different aspects of the flow, i.e., the division of water at two bifurcations in the delta, the effects of the lakes on the flow in the lower part of the system, the area of tidal propagation, are also quantified and discussed.
      PubDate: 2016-01-12
  • Self-aeration in the rapidly- and gradually-varying flow regions of steep
           smooth and stepped spillways
    • Abstract: Abstract In high-velocity chute flows, free-surface aeration is often observed. The phenomenon is called self-aeration or white waters. When the turbulent shear stresses next to the free-surface are large enough, air bubbles are entrained throughout the entire air–water column. A rapidly-varied flow region is observed immediately downstream of the inception point of free-surface aeration. An analytical solution of the air diffusion equation is proposed and the results compare well with new experimental data. Both experiments and theory indicate that the flow bulking spans over approximately 3–4 step cavities downstream of the inception point of free-surface aeration on a stepped chute. Further downstream the void fraction distributions follow closely earlier solutions of the air diffusion equation. The application of the diffusion equation solution to prototype and laboratory data shows air bubble diffusivities typically larger than the momentum transfer coefficient. The result highlights however a marked decrease in the ratio of air bubble diffusivity to eddy viscosity with increasing Reynolds number. The finding might indicate some limitation of laboratory investigations of air bubble diffusion process in self-aerated flows and of their extrapolation to full-scale prototype applications.
      PubDate: 2015-12-24
  • Modeling the interaction between tides and storm surges for the Taiwan
    • Abstract: Abstract An unstructured grid, two-dimensional hydrodynamic model was established and applied to the coast of Taiwan to investigate the tide-surge interaction. Tidal elevations at the open boundaries coupled with a global ocean tidal model and the meteorological conditions using a cyclone model are used to drive the model. The model was calibrated and verified with the observed tidal levels at six tidal stations for seven typhoon events to ascertain the capability and feasibility of the model. The results show reasonable agreement between the simulated and observed tidal levels. The validated model was then applied to probe the influence of tide-surge interaction on phase, water levels, and storm surge height. We found that the tide-surge interaction influenced both the magnitude and timing of the surge, which depended on the typhoon path. The storm surge heights at different tidal stations were significantly influenced by wind stresses and directions. The water level rise due to the storm surge during high tide was greater at neap tide than at spring tide. Changing tidal ranges altered the prediction of the surge enough to induce the changes in peak water levels.
      PubDate: 2015-12-23
  • Near-boundary velocity and turbulence in depth-varying stream flows
    • Abstract: Abstract This research examined the temporal distribution of turbulent structure near a streambank toe through the progression of a flood wave in West Run (Morgantown, WV, USA). Three-dimensional velocities and water depths were measured through a 17-h flood event. Turbulence characteristics were examined: Reynolds stresses, turbulent kinetic energy, and turbulence intensities. On average, near-boundary velocity during the rising stage was less than the falling stage, likely due to the measurement location and local roughness. The velocity vectors shifted from towards bed before the flood wave to toward the streambank during progression of the flood wave. Turbulent kinetic energy increased with increasing water depth during the rising stage. Reynolds stress, τxz, increased with increasing water depth during the rising stage, but the majority of the stresses were negative through the storm event. Reynolds stress, τxy, was positive throughout the event and did not vary with depth. This work is among the first to evaluate turbulence during depth-varying flows in the field.
      PubDate: 2015-12-22
  • A modified log-law of flow velocity distribution in partly obstructed open
    • Abstract: Abstract Flow through rigid and emergent/submerged cylinder arrays are commonly found in several engineering application such as offshore structures, transmission lines, chimneys, array of silos and field array of trees. Various hydrodynamic phenomena may be occurring in the interaction between a flowing fluid and these structures. In this manuscript we focus on the study of flow structures in a channel partially obstructed by an array of equi-spaced, vertical, rigid, emergent, circular steel cylinders. Experimental results show that the presence of the cylinders array strongly affects the flow velocity distribution, forming a transversal sharp transition region at the interface between the obstructed and the unobstructed domains. At the interface, for the current and previous studies, it was observed that the flow distribution always resembles a boundary layer feature. This similarity in feature of the flow distribution as a boundary layer has led to adapting the universal law of the wall to describe the transversal profile of the mean flow velocity, considering, by analogy, the interface separating both domains as a virtual wall. The specific objectives addressed in this study is to propose and validate a new modified log-law predicting the representative transversal profile of the mean flow velocity at the interface between the obstructed and the unobstructed domains. The proposed analytical model is validated by a series of experiments carried out on a very large rectangular channel in the Department of Civil, Environmental, Building Engineering and Chemistry of the Technical University of Bari—Italy. The three-dimensional flow velocity components were measured using a 3D Acoustic Doppler Velocimeter ADV. As a result, it is observed that the measured and the predicted, applying the proposed modified log-law, mean flow velocity data have a perfect matching between them. Moreover, in the second part of the paper, detailed observations on the flow turbulence structure are analyzed and discussed.
      PubDate: 2015-12-21
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