共查询到20条相似文献,搜索用时 0 毫秒
1.
B. Furieri S. Russeil J.-L. Harion C. Turpin J. M. Santos 《Environmental Fluid Mechanics》2012,12(6):533-553
Emission factors are largely used to quantify particle emissions from industrial open storage piles. These factors are based on the knowledge of velocity distribution and flow patterns over the stockpile surface which still requires further research. The aim of the present work is to investigate the airflow characteristics over a single typical oblong pile and in its near-ground surroundings for various wind flow directions. Wind tunnel experiments using an oil-film surface coating technique were carried out for near-wall flow visualization. Numerical simulation results, favorably compared to PIV measurements, were used to allow comparison analysis of flow features. For the stockpile oriented 90° to the wind main direction, typical topology of flow around wall-mounted obstacles were observed, notably a wake zone downstream the pile including two main counter-rotating vortices. Further analysis of numerical wall shear stress distribution and streamlines indicates that two complex three-dimensional vortical flow structures develop downstream the pile. For other incoming wind flow directions (30 and 60°), the flow characteristics over the storage pile greatly differ as a single helical main vortex develops from the pile’s crest. Corresponding high values of wall shear stress are noticed downstream the storage pile. For each configuration studied, downwash and upwash zones are induced by the vortical structures developed. This near-wall flow topology combined with areas of high friction levels may be linked to potential dust emission from the ground surface surrounding industrial stockpiles. 相似文献
2.
The propagation of density current under different boundary conditions is investigated using high resolution direct numerical simulations (DNS). A revised Kleiser and Schumann influence-matrix method is used to treat the general Robin type velocity boundary conditions and the related “tau” error corrections in the numerical simulations. Comparison of the simulation results reveals that the boundary conditions change the turbulent flow field and therefore the propagation of the front. This paper mainly focuses on the effects of boundary conditions and initial depth of the dense fluid. The differences in energy dissipation and overall front development in wall-bounded and open channels are examined. Through DNS simulations, it is evident that with the decrease of initial release depth ratio ( $D/H$ ), the effect of the top boundary becomes less important. In wall-bounded channels, there are three distinctive layers in the vertical distribution of energy dissipation corresponding to the contributions from bottom wall, interface, and top wall, respectively. In open channels, there are only two layers with the top one missing due to the shear free nature of the boundary. It is found that the energy dissipation distribution in the bottom layer is similar for cases with the same $D/H$ ratio regardless the top boundary condition. The simulation results also reveal that for low Reynolds number cases, the energy change due to concentration diffusion cannot be neglected in the energy budget. To reflect the real dynamics of density current, the dimensionless Froude number and Reynolds number should be defined using the release depth $D$ as the length scale. 相似文献
3.
Environmental Fluid Mechanics - Spatial dimensions of bedforms relative to the flow depth are of great interest for both engineers and geoscientists, and continue to be an active area of research.... 相似文献
4.
5.
Kahouadji Lyes Batchvarov Assen Adebayo Idris T. Jenkins Zachary Shin Seungwon Chergui Jalel Juric Damir Matar Omar K. 《Environmental Fluid Mechanics》2022,22(2):367-382
Environmental Fluid Mechanics - In this article, we present a full three-dimensional numerical study of thin liquid films falling on a vertical surface, by solving the full three-dimensional... 相似文献
6.
Environmental Fluid Mechanics - This numerical study investigates the evolution of constant-flux high density fluid introduced vertically to a rotational low-density ambient through a circular... 相似文献
7.
We review the fundamentals of a new numerical modeling technique called Renormalized Numerical Simulation (RNS). The goal
of RNS is to model the drag force produced by high Reynolds-number turbulent flow over objects that display scale-invariant
properties, objects such as tree-like fractals. The hallmark of RNS in this application is that the drag of the unresolved
tree branches is modeled using drag coefficients measured from the resolved branches and unresolved branches (as modeled in
previous iterations of the procedure). In the present paper, RNS is used to study the effects of branch orientation on the
drag force generated by highly idealized trees in which trunk and branches have square cross-section, and the branches all
lie in a plane perpendicular to the incoming flow. Then, the procedure is generalized to the more general case of non-planar
branch arrangements. Results illustrate that RNS may enable numerical modeling of environmental flow processes associated
with fractal geometries using affordable computational resolution. 相似文献
8.
Sandbars are critical to the cross-shore movement of sediment. Prediction of cross-shore sandbar volumes requires knowledge about the functional relationship of sediment transport rate conditions with waves, currents, base slope, sediment property and water depth. In this study, experiments on cross- shore sediment transport were carried out in a laboratory wave channel for initial base slopes of 1/8, 1/10 and 1/15. Using regular waves with different deep-water wave steepness generated by a pedal-type wave generator, bar volumes caused by cross-shore sediment transport are investigated for beach materials with the medium diameter of d50?=?0.25, 0.32, 0.45, 0.62 and 0.80 mm. A non-dimensional equation for sandbar volume was obtained by using linear and non-linear regression methods through the experimental data and was compared with previously developed equations in the literature. The results have shown that the experimental data fitted well to the proposed equation with respect to the previously developed equations. 相似文献
9.
We consider high-Reynolds-number Boussinesq gravity current and intrusion systems in which both the ambient and the propagating “current” are linearly stratified. The main focus is on a current of fixed volume released from a rectangular lock; the height ratio of the fluids $H$ , the stratification parameter of the ambient $S$ , and the internal stratification parameter of the current, $\sigma $ , are quite general. We perform two-dimensional Navier–Stokes simulation and compare the results with those of a previously-published one-layer shallow-water model. The results provide insights into the behavior of the system and enhance the confidence in the approximate model while also revealing its limitations. The qualitative predictions of the model are confirmed, in particular: (1) there is an initial “slumping” stage of propagation with constant speed $u_N$ , after which $u_N$ decays with time; (2) for fixed $H$ and $S$ , the increase of $\sigma $ causes a slower propagation of the current; (3) for some combinations of the parameters $H,S, \sigma $ the fluid released from the lock lacks initially (or runs out quickly of) buoyancy “driving power” in the horizontal direction, and does not propagate like a gravity current. There is also a fair quantitative agreement between the predictions of the model and the simulations concerning the spread of the current. 相似文献
10.
Experimental and numerical analysis of flow instabilities in rectangular shallow basins 总被引:1,自引:1,他引:0
B. J. Dewals S. A. Kantoush S. Erpicum M. Pirotton A. J. Schleiss 《Environmental Fluid Mechanics》2008,8(1):31-54
Free surface flows in several shallow rectangular basins have been analyzed experimentally, numerically and theoretically.
Different geometries, characterized by different widths and lengths, are considered as well as different hydraulic conditions.
First, the results of a series of experimental tests are briefly depicted. They reveal that, under clearly identified hydraulic
and geometrical conditions, the flow pattern is found to become non-symmetric, in spite of the symmetrical inflow conditions,
outflow conditions and geometry of the basin. This non-symmetric motion results from the growth of small disturbances actually
present in the experimental initial and boundary conditions. Second, numerical simulations are conducted based on a depth-averaged
approach and a finite volume scheme. The simulation results reproduce the global pattern of the flow observed experimentally
and succeed in predicting the stability or instability of a symmetric flow pattern for all tested configurations. Finally,
an analytical study provides mathematical insights into the conditions under which the symmetric flow pattern becomes unstable
and clarifies the governing physical processes. 相似文献
11.
Many environmental problems are linked to multiphase flows encompassing ecological issues, chemical processes and mixing or
diffusion, with applications in different engineering fields. The transition from a supercritical flow to a subcritical motion
constitutes a hydraulic jump. This flow regime is characterised by strong interactions between turbulence, free surface and
air–water mixing. Although a hydraulic jump contributes to some dissipation of the flow kinetic energy, it is also associated
with increases of turbulent shear stresses and the development of turbulent eddies with implications in terms of scour, erosion
and sediment transport. Despite a number of experimental, theoretical and numerical studies, there is a lack of knowledge
concerning the physical mechanisms involved in the diffusion and air–water mixing processes within hydraulic jumps, as well
as on the interaction between the free-surface and turbulence. New experimental investigations were undertaken in hydraulic
jumps with Froude numbers up to Fr = 8.3. Two-phase flow measurements were performed with phase-detection conductivity probes.
Basic results related to the distributions of void fraction, bubble frequency and mean bubble chord length are presented.
New developments are discussed for the interfacial bubble velocities and their fluctuations, characterizing the turbulence
level and integral time scales of turbulence representing a “lifetime” of the longitudinal bubbly flow structures. The analyses
show good agreement with previous studies in terms of the vertical profiles of void fraction, bubble frequency and mean bubble
chord length. The dimensionless distributions of interfacial velocities compared favourably with wall-jet equations. Measurements
showed high turbulence levels. Turbulence time scales were found to be dependent on the distance downstream of the toe as
well as on the distance to the bottom showing the importance of the lower (channel bed) and upper (free surface) boundary
conditions on the turbulence structure. 相似文献
12.
Y. Peltier S. Erpicum P. Archambeau M. Pirotton B. Dewals 《Environmental Fluid Mechanics》2014,14(3):699-710
Meandering flows in rectangular shallow reservoirs were experimentally investigated. The characteristic frequency, the longitudinal wave length and the mean lateral extension of the meandering jet were extracted from the first paired modes, obtained by a proper orthogonal decomposition of the surface velocity field measured by large scale PIV. The depth-normalised characteristic lengths and the Strouhal number were then compared to the main dimensionless numbers characterizing the experiments: Froude number, friction number and reservoir shape factor. The normalised wave length and mean lateral extension of the meandering jet are neither correlated with the Froude number nor with the reservoir shape factor; but a clear relationship is found with the friction number. Similarly, the Strouhal number is found proportional to a negative power of the friction number. In contrast, the Froude number and the reservoir shape factor enable to predict the occurrence of a meandering flow pattern: meandering jets occur for Froude number greater than 0.21 and for a shape factor smaller than 6.2. 相似文献
13.
Benchikh Le Hocine Alla Eddine Lacey R. W. Jay Poncet Sébastien 《Environmental Fluid Mechanics》2019,19(2):435-456
Environmental Fluid Mechanics - A numerical benchmark of different turbulence closures was performed to investigate the turbulent wake flow behind a submerged D-shaped bluff body. The numerical... 相似文献
14.
15.
West Indian Ocean phytoplankton: a numerical investigation of phytohydrographic regions and their characteristic phytoplankton associations 总被引:2,自引:0,他引:2
M. Thorrington-Smith 《Marine Biology》1971,9(2):115-137
Phytoplankton samples were collected from a large area of the West Indian Ocean and 237 different species identified. The object of this study was to define structure in the species distributions and to relate this to environmental factors. Numerical methods of cluster analysis are described, with adaptation and application to this ecological study of phytoplankton. The phytoplankton stations were grouped according to their phytoplankton populations; these groupings were related firstly to the monsoon seasons, and secondly to the hydrology, in order to derive phytohydrographic regions. The species were then grouped according to hydrographical distribution in order to derive the floral elements (species associations) which typify the different regions. The samples divided seasonally into 2 overlapping clusters, those sampled prior to the South West Monsoon, and those sampled subsequently. In both seasonal groups 4 main phytohydrographic regions were isolated from (1) equatorial subsurface water; (2) the equatorial undercurrent boundary; (3) the South Equatorial Current; (4) the surface tropical water. A total of 11 different floral elements were derived to account for the phytohydrographic groupings. The distribution of the largest element (50 species) was centred in equatorial subsurface water. This element dominated all samples, and was considered to comprise the endemic Indian Ocean flora. The effects of the other minor floral elements were superimposed on the dominance or otherwise of this element in the samples. These different minor floral elements were characteristic of (a) different seasonal divisions; (b) regional differences in equatorial subsurface water; (c) traversing currents; (d) nutrientrich regions of instability. 相似文献
16.
Kamal El Kadi Abderrezzak André Paquier Bernard Gay 《Environmental Fluid Mechanics》2008,8(2):169-198
This paper reports a numerical study on dam-break waves over movable beds. A one-dimensional (1-D) model is built upon the
Saint-Venant equations for shallow water waves, the Exner equation of sediment mass conservation and a spatial lag equation
for non-equilibrium sediment transport. The set of governing equations is solved using an explicit finite difference scheme.
The model is tested in various idealized experimental cases, with fairly good agreement between the numerical predictions
and measurements. Discrepancies are observed at the earlier stage of the dam-break wave and around the dam location due to
no vertical velocity component being taken into account. Sensitivity tests confirm that the friction coefficient is an important
parameter for the evaluation of sediment transport processes operating during a dam-break wave. The influence of the non-equilibrium
adaptation length (or the lag distance) is negligible on the wavefront celerity and weak on the free surface and bed profiles,
which indicates that one may ignore the spatial lag effect in dam-break wave studies. Finally, the simulation of the Lake
Ha!Ha! dyke-break flood event shows that the model can provide relevant results if a convenient formula for computing the
sediment transport capacity and an appropriate median grain diameter of riverbed material are selected. 相似文献
17.
Yanxiao Si Fang Zhang Hong Chen Guanghe Li Haichuan Zhang Dun Liu 《Frontiers of Environmental Science & Engineering》2021,15(6):112
18.
Kitsikoudis Vasileios Yagci Oral Kirca V. S. Ozgur Kellecioglu Dorukhan 《Environmental Fluid Mechanics》2016,16(6):1283-1308
Environmental Fluid Mechanics - Riparian and floodplain tree-like emergent vegetation alter significantly the flow field and lead to complicated three-dimensional flow patterns, characterized by... 相似文献
19.
Environmental Fluid Mechanics - A series of experiments were conducted to quantify the dynamics of a filling box driven by a line plume that spans the full width of the enclosure. Three... 相似文献
20.
We investigate turbulent mixing in a tidally driven, mid-latitude, shallow-water basin. The study is carried out numerically
at a laboratory-scale, using large-eddy simulation. We compared the results of the simulation with those of a correspondent
purely oscillatory flow (Stokes boundary layer). The effect of rotation on the flow dynamics is twofold. First, rotation gives
rise to a mean spanwise flow that concurs to redistribute the turbulent energy among the Reynolds stresses, in particular
between the horizontal directions, thus increasing the mixing across the water column and thickening the layer where developed
turbulence is observable. Second, the presence of the horizontal component of the background vorticity (latitude effect) breaks
the symmetry between the two semi-cycles of the oscillation, since turbulence results suppressed/enhanced during the first/second
semi-cycle. These two effects significantly modify the turbulent characteristics with respect to the purely oscillating flow,
although the mechanisms that generates turbulence present similar features. The qualitative agreement between our results
and some measurements carried out in two sites with characteristics similar to the case analyzed suggests that the outcomes
here provided may be of general use for the analysis of mid-latitude, neutrally stratified, shallow-water basins mainly driven
by semi-diurnal tidal currents. 相似文献