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Přístupy uplatňované pro modelování rozptylu těžkého plynu
Jaňour, Zbyněk
Ve zprávě jsou popsány základní metody popisu proudění v Mezní vrstvě atmosféry a difúze plynů se zaměřením na plyny těžké. Stručně jsou naznačeny problémy experimentů v přírodě (in situ), je uvedena metoda fyzikálního modelování a jsou popsány matematické modely pro tento problém užívané. Je uvedena struktura těchto modelů od modelů pro tzv. blízké pole po modely popisující pole vzdálené. Jsou popsány tzv. provozní modely, jejichž předností je relativní jednoduchost, rychlost získání výsledků i pokusů o popis vlivů topografie, typu zdrojů apod. a jsou uvedeny jejich nedostatky. Dále jsou zavedeny tzv. CFD modely používané pro Mezní vrstvu atmosféry. Součástí modelů jsou i počáteční podmínky (pro nestacionární zdroje) a podmínky okrajové. Pro ověření použitelnosti modelů a zejména jejich numerického řešiče jsou popsány metod jejich verifikace a validace kompletního matematického modelu.
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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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