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Approaches for the modelling of heavy gas dispersion
Jaňour, Zbyněk
The report describes the basic methods of description of the flow in the boundary layer of the atmosphere and the diffusion of gases with a focus on the gas hard. The experiments are discussed briefly the problems in nature (in situ), shows the method of physical modelling and describes the mathematical models used for this problem. The report shows the structure of these models from the model for the so-called a nearby field after the models describing the far field. It follows so-called operational models, whose advantage is the relative simplicity, speed of getting results and attempts to type the description of the effects of topography, resources, etc. and are given their shortcomings. The following are introduced so called CFD models that are used for the marginal layer of the atmosphere. Part of the models is the initial conditions (for non-stationary sources) and the boundary conditions. For the verification of the applicability of the model and in particular their numerical solvers are described methods of verification and validation of mathematical models.
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Neutrally stratified flow modelling over complex terrain at meso-scale: open-cut coal mine study
Nosek, Štěpán ; Jaňour, Zbyněk ; Jurčáková, Klára ; Kellnerová, Radka ; Kukačka, Libor
The objective of this case study was to determine the influence of the coal mine cavity and its vicinity on the main flow field with respect to prevailing wind direction. In order to model the neutrally stratified flow over extremely huge open-cut coal mine Libouš situated at north-west of Czech Republic the laminar flow analogy was applied. The model was scaled down to 1:9000 according to dimensions of wind-tunnel and selected coal mine surroundings. The measurements of longitudinal and lateral velocity components in selected vertical, resp. horizontal planes were performed by LDA. The measured data will be used for validation of CFD simulation and for selections of area of interest at bigger scales where turbulent flow modelling will be performed. The results revealed that not only of cavity shape and deepness but also the surroundings orography has influence on flow pattern, hence on ventilation, within the area of interest.
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Quadrant analysis of turbulent pollution flux above the modelled street intersection
Kukačka, Libor ; Nosek, Štěpán ; Kellnerová, Radka ; Jurčáková, Klára ; Jaňour, Zbyněk
The objective of this experimental study is to determine processes of a vertical turbulent pollution transport above the X-shaped street intersection in an idealised symmetric urban area for several approach flow directions. An experimental set-up for simultaneous measurement of the flow velocity and the tracer gas con-centration in a high temporal resolution is assembled. Vertical turbulent scalar fluxes are computed from the measured data in a horizontal plane above the street intersection. The quadrant analysis was applied to the vertical turbulent pollution fluxes data. Events with dominant contribution to vertical turbulent pollution flux were detected. The mean duration, repetition frequency and the duration percentage were computed for these events. A strong influence of the approach flow direction on the type of dominant events and their characteristics was resolved.
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Numerical simulation of 3D flows in atmospheric boundary layer
Šimonek, Jiří ; Kozel, K. ; Jaňour, Zbyněk
The work deals with the numerical solution of 3D turbulent stratified flows in atmospheric boundary layer over the cosine function shaped hill. Mathematical model for the turbulent stratified flows in atmospheric boundary layer is the Boussinesq model - Reynolds averaged Navier-Stokes equations (RANS) for incompressible turbulent flows with addition of the transport equation for density and that is coupled with the RANS system by the source term at the right hand side of the momentum equation. The artificial compressibility method and the finite volume method have been used in all computed cases and Lax-Wendroff scheme (MacCormack form) has been used together with the Cebecci-Smith algebraic turbulence model.
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Physical modelling of pollution dispersion in complex terrain situation
Jurčáková, Klára ; Jaňour, Zbyněk ; Kellnerová, Radka ; Kukačka, Libor
Abstract. Airflow in the lowest part of atmosphere is due to high intensity turbulence very complicated process. This is a reason why simple and reliable model for dispersion of air pollution from its source to receptor still does not exist. Physical modelling, in which frame the model of area of interest is made, is an alternative method next to mathematical modelling. Flow and pollution dispersion is examined in the special wind tunnel in detail. Methodology of experiment preparation and of experiment itself as well as a few selected case studies will be presented in the contribution.
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On the thermally stratified atmospheric flow modeling
Sládek, Ivo ; Kozel, K. ; Jaňour, Zbyněk
The paper deals with a numerical study devoted to thermally /indifferently stratified atmospheric boundary layer flow. The main objective is related to definition of the model and flow conditions as well as to presentation of some first numerical results concerning the flow over selected hill configuration under the indifferent thermal conditions. The mathematical model is based on the system of Reynolds-averaged Navier Stokes (RANS)equations closed by two-equation k-e turbulence model together with wall functions.The thermal stratification is modeled using transport equation for the potential temperature. The finite volume method and the explicit Runge-Kutta time integration method are utilized for the numerics. A 2D-hill test case with a rough wall has been chosen to perform numerical test.
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