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  • Articles  (434)
  • Springer  (434)
  • American Physical Society (APS)
  • Blackwell Publishing Ltd
  • Elsevier
  • 2010-2014  (434)
  • Environmental Fluid Mechanics  (207)
  • 9461
  • Architecture, Civil Engineering, Surveying  (434)
  • 1
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    Mixing layer in open-channel junction flows (2013)
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    Publication Date: 2013-09-09
    Description: When two open-channel flows merge in a three-branch subcritical junction, a mixing layer appears at the interface between the two inflows. If the width of the downstream channel is equal to the width of each inlet channel, this mixing layer is accelerated and is curved due to the junction geometry. The present work is dedicated to simplified geometries, considering a flat bed and a $90^{\circ }$ 90 ∘ angle where two configurations with different momentum ratios are tested. Due to the complex flow pattern in the junction, the so-called Serret–Frenet frame-axis based on the local direction of the velocity must be employed to characterize the flow pattern and the mixing layer as Cartesian and cylindrical frame-axes are not adapted. The analysis reveals that the centerline of the mixing layer, defined as the location of maximum Reynolds stress and velocity gradient, fairly fits the streamline separating at the upstream corner, even though a slight shift of the mixing layer towards the center of curvature is observed. The shape of the mixing layer appears to be strongly affected by the streamwise acceleration and the complex lateral confinement due to the side walls and the corners of the junction, leading to a streamwise increase of the mean velocity along the centerline and a decrease of the velocity difference. This results in a specific streamwise evolution of the mixing layer width, which reaches a plateau in the downstream region of the junction. Finally, the evaluation of the terms in the Reynolds-Averaged-Navier–Stokes equations reveals that the streamwise and normal acceleration and the pressure gradient remain dominant, which is typical of accelerated and rotational flows.
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Geosciences
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  • 2
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    Prediction of pollutant dispersion in turbulent two-phase flows (2013)
    Springer
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    Publication Date: 2013-09-16
    Description: With a growing awareness of water pollution problems, in recent years there has been a considerable increased effort in developing and applying numerical models to predict accurately the contaminant distributions, particularly in free surface flows. This numerical study presents a predictive hydrodynamic model in order to explore the dispersion phenomenon of a pollutant injected from time-dependent sources in a turbulent free surface flow. More precisely, we study the impact of pulsation on the dispersion of an injected material. The air/water interface was modeled with the volume of fluid method and sharpness of the free surface was assured by means of Geo-Reconstruct scheme. The numerical results showed that the pulsation played a dominant role at the early stage of the pollutant transport. It was also observed that the pulsation affected the distribution of the injected material especially near the front and that a major swirling action was developed compared to the constant-rate-injection case.
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Geosciences
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  • 3
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    Turbulent flow characteristics and drag over 2-D forward-facing dune shaped structures with two different stoss-side slopes (2013)
    Springer
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    Publication Date: 2013-09-21
    Description: The present paper explores the characteristics of turbulent flow and drag over two artificial 2-D forward-facing waveform structures with two different stoss side slopes of $50^{\circ }$ 50 ∘ and $90^{\circ },$ 90 ∘ , respectively. Both structures possessed a common slanted lee side slope of $6^{\circ }.$ 6 ∘ . Flume experiments were conducted at the Fluvial Mechanics Laboratory of Indian Statistical Institute, Kolkata. The velocity data were analyzed to identify the spatial changes in turbulent flow addressing the flow separation region with recirculating eddy, the Reynolds stresses, the turbulent events associated with burst-sweep cycles and the drag over two upstream-facing bedforms for Reynolds number $Re_h=1.44\times 10^5.$ R e h = 1.44 × 10 5 . The divergence at the stoss side slope between the two structures revealed significant changes in the mean flow and turbulence. Comparison showed that during the flood-tide condition there was no flow separation region on the gentle lee side of the structure with smaller slope at the stoss side, while for the other structure with vertical stoss side slope a thick flow separation region with recirculating eddy was observed at the gentle lee side just downstream of the crest. The recirculating eddy induced on the lee-side had a strong influence on the resistance that the structure exerts to the flow due to loss of energy through turbulence. In contrast, a great amount of reduction in drag was observed in the case of smaller stoss side sloped structure as there was no flow separation. The quadrant analysis was also used to highlight the turbulent event evolution along the bed form structures under flood-tide conditions.
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  • 4
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    Waves of intermediate length through an array of vertical cylinders (2013)
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    Publication Date: 2013-09-28
    Description: We report a semi-analytical theory of wave propagation through a vegetated water. Our aim is to construct a mathematical model for waves propagating through a lattice-like array of vertical cylinders, where the macro-scale variation of waves is derived from the dynamics in the micro-scale cells. Assuming infinitesimal waves, periodic lattice configuration, and strong contrast between the lattice spacing and the typical wavelength, the perturbation theory of homogenization (multiple scales) is used to derive the effective equations governing the macro-scale wave dynamics. The constitutive coefficients are computed from the solution of micro-scale boundary-value problem for a finite number of unit cells. Eddy viscosity in a unit cell is determined by balancing the time-averaged rate of dissipation and the rate of work done by wave force on the forest at a finite number of macro stations. While the spirit is similar to RANS scheme, less computational effort is needed. Using one fitting parameter, the theory is used to simulate three existing experiments with encouraging results. Limitations of the present theory are also pointed out.
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  • 5
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    A three-dimensional experimental investigation of the structure of the spanwise vortex generated by a shallow vortex dipole (2013)
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    Publication Date: 2013-06-08
    Description: The three-dimensional dynamics of shallow vortex dipoles is investigated by means of an innovative three-dimensional, three-component (3D-3C) scanning PIV technique. In particular, the three-dimensional structure of a frontal spanwise vortex is characterized. The technique allows the computation of the three-dimensional pressure field and the planar (x, y) distribution of the wall shear stress, which are not available using standard 2D PIV measurements. The influence of such a complex vortex structure on mass transport is discussed in the context of the available pressure and wall shear stress fields.
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  • 6
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    Turbulence and aeration in hydraulic jumps: free-surface fluctuation and integral turbulent scale measurements (2013)
    Springer
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    Publication Date: 2013-04-10
    Description: In an open channel, a change from a supercritical to subcritical flow is a strong dissipative process called a hydraulic jump. Herein some new measurements of free-surface fluctuations of the impingement perimeter and integral turbulent time and length scales in the roller are presented with a focus on turbulence in hydraulic jumps with a marked roller. The observations highlighted the fluctuating nature of the impingement perimeter in terms of both longitudinal and transverse locations. The results showed further the close link between the production and detachment of large eddies in jump shear layer, and the longitudinal fluctuations of the jump toe. They highlighted the importance of the impingement perimeter as the origin of the developing shear layer and a source of vorticity. The air–water flow measurements emphasised the intense flow aeration. The turbulent velocity distributions presented a shape similar to a wall jet solution with a marked shear layer downstream of the impingement point. The integral turbulent length scale distributions exhibited a monotonic increase with increasing vertical elevation within 0.2 〈 L z /d 1 〈 0.8 in the shear layer, where L z is the integral turbulent length scale and d 1 the inflow depth, while the integral turbulent time scales were about two orders of magnitude smaller than the period of impingement position longitudinal oscillations.
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  • 7
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    The effect of non-uniform depth on the baroclinic response to wind in elongated basins (2013)
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    Publication Date: 2013-04-10
    Description: We examined the effect of along-thalweg depth variability on the baroclinic response to wind in elongated narrow basins with a sharp thermocline. The effect of depth variability was examined by deriving a modal-based forced model with two density layers and applying the model to a symmetric curved-bottom basin (CB), an asymmetric wedge-shaped basin (with a sloping bottom towards a vertical wall, WB), and a flat-bottom basin (FB). The baroclinic responses of CB, WB, and FB to uniform wind were found to differ in time-scale, number and energy of excited modes, and temporal pattern and along-thalweg structure of baroclinic flow and thermocline deflection. For all bottom profiles that were examined, the fundamental mode was found to dominate the response to spatially-uniform wind. Compared to FB, the asymmetric depth variability in WB increased the number and energy of excited higher modes and localized the interface shear, while the symmetric deviation from flat bottom in CB caused the opposite effects. Linear deviation from uniform wind was found to feed energy into higher baroclinic modes for the symmetric CB, but was found to reduce the energy of higher baroclinic modes for WB when the deviation from uniform wind is comparable to the spatial-average magnitude. Our results can explain the observation of the second baroclinic mode and irregular wave patterns in some lakes and reservoirs. Further, our results suggest that one-dimensional vertical mixed-layer models provide better results for shear entrainment in curved-bottom basins than in wedge-shaped basins.
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  • 8
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    New analytical formulations for calculation of dispersion parameters of Gaussian model using parallel CFD (2013)
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    Publication Date: 2013-04-10
    Description: New analytical formulations are presented for calculation of most effective parameters in the Gaussian plume dispersion model; the standard deviations of concentration for horizontal and vertical dispersion in neutral atmosphere conditions. Employing parallel Computational Fluid Dynamics (CFD) as a powerful tool, some well-known analytical generations of Pasquill–Gifford–Turner experimental data are modified. To achieve this aim, CFD simulations are carried out for single stack dispersion on flat terrain surface and ground level concentrations are determined in different distances. An inverse procedure in Gaussian plume dispersion model is then applied and standard deviations of horizontal and vertical dispersions are obtained. The values are compared with those of the well-known methods of Doury, Briggs and Hanna in two cases: the experimental data for release of krypton-85 from 100 m high and pollution dispersion from three 28 m high stacks of Besat power plant near Tehran. The comparison indicates that new formulations for plume dispersion are more accurate than other well-known formulations.
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  • 9
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    Similarity relations in a stable and relatively neutral surface layer in an urban area with complex topography (Tehran) (2013)
    Springer
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    Publication Date: 2013-04-10
    Description: In this paper the flow and turbulent structures are investigated over the city of Tehran (an urban area located in a basin surrounded by high mountains in the north and east). A number of non-dimensional parameters are investigated in the frame work of Monin–Obukhov similarity theory (MOST) using a local scaling approach. These parameters include dimensionless wind gradient, normalized standard deviations of three components of wind and dimensionless momentum fluxes. The main purpose of this paper is to evaluate MOST in predicting the above parameters for the selected terrain at 15 and 105 m heights. The prevailing conditions are stable and relatively neutral, based on stability parameter using local Obukhov length. For this study, data of a PA1 SODAR with supplementary data of a 100-m tower with four 2D sonic anemometers and also a 2D sonic anemometer installed at 2 m height have been used. Our results confirm that the non-dimensional parameters could be collapsed in to the similarity expressions only at 105 m height (that lies in the inertial sub-layer) not at 15 m height (that belongs to the roughness sub-layer). It is important to note that the obtained empirical constants for all of the considered parameters show considerable differences with those reported by others for other surface types. This is attributed to the local effects for where that the topographic wave forcing may need special considerations. This robustly emphasizes the importance of MOST validation for urban area with topography as Tehran. Consequently, MOST has been successfully verified at 105 m for Tehran data set with new empirical constants.
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  • 10
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    An approach to simulate wind fields around an urban environment for wind energy application (2013)
    Springer
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    Publication Date: 2013-04-10
    Description: This work proposes an approach to simulate wind flow fields around an urban environment with the aim of evaluating the potential impact of buildings on the general wind patterns and power production using the current generation of commercial wind turbines. The simulation process was performed with the aid of accessible computational tools that can potentially render the proposed procedure applicable in other cases of interest. The roughness of the urban environment was defined as the association of roughness map, topography, and an alternative process for obtaining the volumetry of buildings. A case study was conducted in a region located at the district of Boa Viagem (Recife-PE) for assessing the applicability of the approach. Scenarios were designed in order to simulate wind flow patterns and pre-identify sites that have suitable wind energy potential for electric power production by investigating the combination of wind speed magnitude and turbulence intensity. From the results obtained, it was possible to identify zones of potential wind sources that are not detected in classical wind atlas probably due to the influence of the built environment on local wind flow patterns.
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    Topics: Architecture, Civil Engineering, Surveying , Geography , Geosciences
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