Environmental Fluid Mechanics Research Papers (original) (raw)

Hydrodynamics of vegetated channels and streams is a rapidly developing research area, and this chapter summarizes the current knowledge considering both aquatic and riparian zones. The benefit of an advanced parameterization of plant... more

Hydrodynamics of vegetated channels and streams is a rapidly developing research area, and this chapter summarizes the current knowledge considering both aquatic and riparian zones. The benefit of an advanced parameterization of plant morphology and biomechanical properties is highlighted. For this purpose, the response of flexible and foliated plants and plant communities to the flow is illustrated, and advanced models for the determination of drag forces of flexible plants are described. Hydrodynamic processes governing flow patterns in vegetated flows are presented for submerged and emergent conditions considering spatial scales ranging from the leaf to the vegetated reach scale.

The Navier-Stokes differential equations describe the motion of fluids which are incompressible. The three-dimensional Navier-Stokes equations misbehave very badly although they are relatively simple-looking. The solutions could wind up... more

The Navier-Stokes differential equations describe the motion of fluids which are incompressible. The three-dimensional Navier-Stokes equations misbehave very badly although they are relatively simple-looking. The solutions could wind up being extremely unstable even with nice, smooth, reasonably harmless initial conditions. A mathematical understanding of the outrageous behaviour of these equations would dramatically alter the
field of fluid mechanics. This paper describes why the three-dimensional Navier-Stokes equations are not solvable, i.e., the equations cannot be used to model turbulence, which is
a three-dimensional phenomenon.

All forms of life on earth are immersed in natural fluids, such as the air in the atmosphere and the water in surface and underground systems. The knowledge of natural fluids motions is therefore very important and lead to the... more

All forms of life on earth are immersed in natural fluids, such as the air in the atmosphere and the water in surface and underground systems. The knowledge of natural fluids motions is therefore very important and lead to the implementation of a new discipline, termed Environmental Fluid Mechanics (EFM). EFM is the scientific study of naturally occurring fluid flows of air and water on our planet Earth, especially of those flows that affect the environmental quality of air and water. In this chapter EFM is introduced. First commonalities and differences between EFM and its cousin disciplines, such as Fluid Mechanics, Hydraulics and Geophysical Fluid Dynamics, are described pointing out their specific purpose and scales. Second, the concepts of stratification and turbulence, which are two essential ingredients of EFM, are introduced. Third, scales, processes and systems within EFM are presented. The concept of environmental interface is defined introducing the EFM processes occurring across the main four environmental interfaces. The chapter ends with a discussion about the challenges facing EFM scientists in the next decades.

Extensive Experiments on inclined dense jets typical of brine discharges into shallow water are reported. The experiments were conducted with nozzles oriented at 30°, 45°, and 60° to the horizontal and the spatial variations of tracer... more

Extensive Experiments on inclined dense jets typical of brine discharges into shallow water are reported. The experiments
were conducted with nozzles oriented at 30°, 45°, and 60° to the horizontal and the spatial variations of tracer concentrations were measured by three-dimensional laser-induced fluorescence (3DLIF). Three flow regimes were identified: deep water, surface contact, and shallow water. The regimes depend on the value of dF=H, where d is the nozzle diameter, F the jet densimetric Froude number, and H the water depth; criteria were presented for the transitions between them. Flow images revealed complex three-dimensional interactions with the free surface, especially for steep nozzle angles in shallow water. Dilutions at critical points and their locations were measured. For deep water, all
results followed those previously reported for fully submerged jets. As the depth decreases (or dF=H increases) to the surface contact regime, dilutions begin to decrease. Tracer concentration profiles are truncated at the water surface and in shallow water resemble half-Gaussian profiles similar to those of wall jets. The jets can cling to the water surface, although the locations of the bottom impact point and near-field
length are not significantly affected by the water surface. In deep water and surface contact regimes, the impact point and near-field dilutions
are highest for 60° nozzles. As the depth decreases further, however, the dilutions for the three nozzle angles become approximately equal, until, for shallow water, the 30°-nozzle gives slightly higher dilution. The 30°-nozzle may be preferable for this case because there is less
surface interaction and, therefore, less visual impact on the water surface. Previous recommendations that dense jets be submerged so that the rise height to the jet’s upper boundary be less than 75% of the water depth to avoid surface effects appear to be overly conservative and the present results suggest that the rise can be as much as 90% of the water depth for all angles with no deleterious effect on dilution.

This reports gives fundamentals of environmental fluid mechanics

Atmospheric air pollution turbulent fluxes can be assumed to be proportional to the mean concentration gradient. This assumption, along with the equation of continuity, leads to the advection-diffusion equation. Moreover, large eddies are... more

Atmospheric air pollution turbulent fluxes can be assumed to be proportional to the mean concentration gradient. This assumption, along with the equation of continuity, leads to the advection-diffusion equation. Moreover, large eddies are able to mix scalar quantities in a manner that is counter to the local gradient. We present a general solution of a two-dimension steady state advection-diffusion equation, considering non-local turbulence closure using the General Integral Laplace Transform Technique. We show some examples of applications of the new solution with different vertical diffusion parameterisations.

We present and discuss the results of a comprehensive study addressing the non-aerated region of the skimming flow in steep stepped spillways. Although flows in stepped spillways are usually characterized by high air concentrations... more

We present and discuss the results of a comprehensive study addressing the non-aerated region of the skimming flow in steep stepped spillways. Although flows in stepped spillways are usually characterized by high air concentrations concomitant with high rates of energy dissipation, the non-aerated region becomes important in small dams and/or spillways with high specific discharges. A relatively large physical model of such spillway was used to acquire data on flow velocities and water levels and, then, well-resolved numerical simulations were performed with a commercial code to reproduce those experimental conditions. The numerical runs benefited from the ability of using multi-block grids in a Cartesian coordinate system, from capturing the free surface with the TruVOF method embedded in the code, and from the use of two turbulence models: the k−varepsilon{k{-}\varepsilon}k−varepsilon and the RNG k−varepsilon{k{-}\varepsilon}k−varepsilon models. Numerical results are in good agreement with the experimental data corresponding to three volumetric flow rates in terms of the time-averaged velocities measured at diverse steps in the spillway, and they are in very satisfactory agreement for water levels along the spillway. In addition, the numerical results provide information on the turbulence statistics of the flow. This work also discusses important aspects of the flow, such as the values of the exponents of the power-law velocity profiles, and the characteristics of the development of the boundary layer in the spillway.

Laboratory experiments on single dense jets oriented at angles from 15° to 85° to the horizontal are reported. The major flow properties were measured by laser-induced fluorescence at the maximum rise height, impact point, and, for the... more

Laboratory experiments on single dense jets oriented at angles from 15° to 85° to the horizontal are reported. The major flow
properties were measured by laser-induced fluorescence at the maximum rise height, impact point, and, for the first time, at the end of the near
field. The impact point dilution was insensitive to nozzle angle over the range of about 45–65°. Because the additional mixing that occurred in
the spreading layer beyond the impact point depended on nozzle angle, the near-field dilution was more sensitive to nozzle orientation and was highest for 60°, consistent with generally accepted design practice. Bottom boundary effects on dilution were also addressed. Along the jet centerline, time-average dilution first increased and then actually decreased in a thin layer up to the wall. The concentration increase near
the bed is due to an increase in turbulent intermittency and accumulation of more saline fluid elements at the bed. The presence of this layer may explain wide discrepancies in reported dilutions near the boundary and may be environmentally important due to exposure of benthic
organisms and sea grasses to high salinity. It may not persist, however, as it can be swept up by vortices that propagate radially away from the impact point. The vortices entrain ambient fluid leading to increased dilution, but they eventually collapse under their self-induced density stratification, marking the end of the near field.

There are many industrial sites where open aggregate conical piles exist to store granular materials, like coal, industrial residuals, or other minerals. Usually these storage piles are placed in open areas, making them susceptible to... more

There are many industrial sites where open aggregate conical piles exist to store granular materials, like coal, industrial residuals, or other minerals. Usually these storage piles are placed in open areas, making them susceptible to wind erosion, which can create health, environmental, and/or economical concerns. It is common to minimize the dust emission through the placement of windbreaks in the vicinity of the storage piles, which reduces the wind speed in the vicinity of the pile’s surface. In this work, some experimental results from a wind tunnel study on the erosion of a conical sand pile, exposed or protected by a fence with porosities of 0, 70, and 83%, are shown. For the sheltered cases, the windbreak was placed at several distances from the pile’s leading edge, ranging from H to 4H, where H is the initial height of the non-eroded pile. The evolution of the shape of the sand pile is shown, at different instances in time, and the pile deformation quantified, using a novel experimental setup developed for wind erosion studies. This information might be regarded as a useful dataset for the benchmark of computational models aiming to produce the transient simulation of the aeolian erosion of stockpiles. The CFD results are comprised of the modeling of several experimental scenarios. The computational results for the surface wind velocity show a good correlation with the initial deformation of the pile. Based on the results, the isocontours of (us /ur ) presented might be regarded as a good basis for the estimation of the pile shear velocity.

The motion of fluids which are incompressible could be described by the Navier-Stokes differential equations. However, the three-dimensional Navier-Stokes equations for modelling turbulence misbehave very badly although they are... more

The motion of fluids which are incompressible could be described by the Navier-Stokes differential equations. However, the
three-dimensional Navier-Stokes equations for modelling turbulence misbehave very badly although they are relatively simple-looking. The solutions could wind up being extremely unstable even with nice, smooth, reasonably harmless initial conditions. A mathematical understanding of the outrageous behaviour of these equations would greatly affect the field of fluid mechanics. In this paper, which had been published in an international journal in 2010, a reasoned, practical approach towards resolving the issue is adopted and a practical, statistical kind of mathematical solution is proposed.

Predictions from a k-ε model are compared with recently acquired experimental data from inclined negatively buoyant discharges. The k-ε model is part of a standard computational fluid dynamics package (CFX). Two approaches are taken when... more

Predictions from a k-ε model are compared with recently acquired experimental data from inclined negatively buoyant discharges. The k-ε model is part of a standard computational fluid dynamics package (CFX). Two approaches are taken when implementing the model. One involves using an essentially standard form of the model to predict flow behaviour. The other approach involves calibrating the model, through adjustment of the turbulent Schmidt number in the tracer transport equation, to achieve reasonable predictions for positively buoyant vertical discharges and then applying it to inclined negatively buoyant discharges. While the calibrated approach improves the predictions of some bulk parameters (notably the tracer spread and dilution) when compared to predictions from the standard model, the overall effect on the quality of the predictions is small. Comparisons with experimental data indicate that predictions from both the standard and calibrated simulations compare favourably with trajectory data, but integrated dilution predictions at the centreline maximum height are conservative (mean-integrated concentrations are over-predicted). The standard and calibrated k-ε predictions confirm the importance of buoyant instabilities on the lower (inner) side of the flow, the effects of which are clearly evident in the mean concentration profiles. However, these simulations have a tendency to overestimate the influence of stabilizing density gradients on the upper (outer) side of the flow and are unable to effectively predict the cross-sectional distribution of a tracer. In contrast to a previous study, the above comparisons indicate that predictions of bulk parameters from such models can be poor and indeed are no better than those obtained from relatively simple analytical solutions.

This paper investigates the determination of flow resistance caused by stiff and flexible woody vegetation. A new procedure has been developed which allows the determination of friction factor f or Manning's n using measurable... more

This paper investigates the determination of flow resistance caused by stiff and flexible woody vegetation. A new procedure has been developed which allows the determination of friction factor f or Manning's n using measurable characteristics of vegetation and flow. The procedure is capable of predicting flow resistance due to: (1) leafless bushes or trees and (2) leafy bushes or trees. The application of the procedure is limited to non-submerged flow (h ≤ H) and relatively low velocity (U 1 m/s), which are typical conditions in low-gradient stream valleys, floodplains and wetlands. The procedure is novel in that it uses sound hydraulic principles and methods that are available but incorporates some adjustments based on the knowledge on mechanical design of trees and deformation of foliage in a flow. The procedure is able to account for the natural branched structure in determining area or volume of a woody plant. This makes the prediction of resistance caused by plants more accurate than if they were treated as arbitrary cylinders. The accuracy of the approach to estimate f and U was somewhat better for the leafless condition (mean error of f was −5% to +4%) compared to the leafy condition (mean error of f was −9% to −3%). The presented procedure is intended as a practical tool for estimating the relationship between plant characteristics and flow resistance for flows over floodplains and wetlands growing woody vegetation.

Πρόκειται για το άρθρο στο Θεσσαλικό Ημερολόγιο 76 σχετικά με το πέτρινο γεφύρι και το μαντάνι της Γιάνναινας στην Ελασσόνα - This is the paper on Journal for the study of Thessalian History about the stone bridge and the water fulling... more

Πρόκειται για το άρθρο στο Θεσσαλικό Ημερολόγιο 76 σχετικά με το πέτρινο γεφύρι και το μαντάνι της Γιάνναινας στην Ελασσόνα - This is the paper on Journal for the study of Thessalian History about the stone bridge and the water fulling device of Giannaina, Elassona

A one-equation turbulence model is presented, in which the turbulent kinetic energy k is calculated with a transport equation whereas the turbulent length scale l is calculated with an algebraic expression. The value of l depends on the... more

A one-equation turbulence model is presented, in which the turbulent kinetic energy k is calculated with a transport equation whereas the turbulent length scale l is calculated with an algebraic expression. The value of l depends on the local stratification and reduces to the classical ?|z| scaling for unstratified flows near a wall, where |z| is the distance to the

In a recent paper published in this journal, Jeon et al. ((2007), Environ Fluid Mech 7(4): 317–329) have presented a new empirical equation for the transverse dispersion coefficient in natural streams that was developed based on the... more

In a recent paper published in this journal, Jeon et al. ((2007), Environ Fluid Mech 7(4): 317–329) have presented a new empirical equation for the transverse dispersion coefficient in natural streams that was developed based on the hydraulic and geometric parameters using a regression technique. A total of 32 data sets collected in 32 streams was used. Among them, 16 data sets were used for deriving the new equation, and the other 16 were used for verifying the equation. Starting from dimensional analysis the authors found that transverse dispersion coefficient depends on three parameters, such as sinuosity, aspect ratio and a friction term. The robust least square method was applied to estimate regression coefficients resulting in an equation which allows better prediction of transverse dispersion coefficient than previous literature equations. The discussers would like to highlight some points raised in the paper.

An event in November 2007 in Ascó-1 nuclear power plant (NPP) in Spain, originated the release of a significant amount of active metallic particles through the discharge stack. Particles were dispersed and deposited in roofs and... more

An event in November 2007 in Ascó-1 nuclear power plant (NPP) in Spain, originated the release of a significant amount of active metallic particles through the discharge stack. Particles were dispersed and deposited in roofs and neighbouring areas within the NPP controlled area. However, the event was not detected until March 2008. More than 1,300 active points with radioactive particles were found, 94 % located inside the double fenced controlled area and 6 % within the exclusion area; 5 particles were found out of the exclusion area. To provide additional insights on the potential consequences of the release, a computational fluid dynamics (CFD) code, ANSYS-CFX-11, has been used to investigate the near-range atmospheric dispersion and deposition of the particles. The purpose of the analysis was to assess the distance travelled by particles of different sizes. A very detailed model of the site was built, taking into account the buildings and the terrain features including the river valley and the surrounding hills. The modelled domain was 3.2 \times 5.2\, \mathrm{km}$$3.2×5.2km, with the atmospheric layer up to 4 km height. The atmospheric conditions recorded during the different periods of time between November 2007 and January 2008 were classified into 37 representative categories. In general, the distribution of the particles found was adequately reproduced by the numerical model. Particles larger than 100\,{\upmu }$$100μm could not travel beyond the double fence. Particles between \mathrm{50\;and\;100}\,{\upmu }$$50and100μm could have been deposited mainly within the exclusion area, with a small probability of travelling farther. Smaller particles could have travelled beyond, but also should have been deposited in the nearby area, while the majority of particles found are larger, thus indicating that the size of the released particles should be above 50\,{\upmu }$$50μm. The detailed CFD simulation allowed answering relevant questions concerning the possibility of having an impacted region larger than the exclusion area.

Fluid Kinematics: Streamline, path line, streak line, stream surface, stream tube, classification of flows: steady, unsteady, uniform, non-uniform, laminar, turbulent flows. One dimensional approximation, examples of real 1-D flows, two... more

Fluid Kinematics: Streamline, path line, streak line, stream surface, stream tube, classification of flows: steady, unsteady, uniform, non-uniform, laminar, turbulent flows. One dimensional approximation, examples of real 1-D flows, two dimensional approximations, 2-D flow in wind tunnel, continuity equations for 1-D and 2-D flows both compressible and incompressible, stream function for two dimensional incompressible flows. Vorticity, rotational flow, Velocity potential function.

Cage-based aquaculture has been growing rapidly in recent years. In some locations, cage-based aquaculture has resulted in the clustering of large quantities of cages in fish farms located in inland lakes or reservoirs and coastal... more

Cage-based aquaculture has been growing rapidly in recent years. In some locations, cage-based aquaculture has resulted in the clustering of large quantities of cages in fish farms located in inland lakes or reservoirs and coastal embayments or fjords, significantly affecting flow and mass transport in the surrounding waters. Existing studies have focused primarily on the macro-scale flow blockage effects of fish cages, and the complex wake flow and associated near-field mass transport in the presence of the cages remain largely unclear. As a first step toward resolving this knowledge gap, this study employed the combined Particle Image Velocimetry and Planar Laser Induced Fluorescence (PIV-PLIF) flow imaging technique to measure turbulence characteristics and associated mass transport in the near wake of a steady current through an aquaculture cage net panel in parametric flume experiments. In the near-wake region, defined as ~3M (mesh size) downstream of the net, the flow turbulen...