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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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On the validation study devoted to stratified atmospheric flow over an isolated hill
Sládek, Ivo ; Kozel, Karel ; Jaňour, Zbyněk
The paper deals with description of the validation model, °ow conditions and mainly it presents some numerical results. Reference and input data for the validation study are based on work of Eidsvik [3]. The mathematical model is based on the system of RANS-equations closed by two-equation k ¡ " turbulence model together with wall functions. The thermal strati¯cation is modeled using transport equation for the potential temperature. The ¯nite volume method and the explicit Runge{Kutta time integration method are utilized for the numerics.
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Změny v pravděpodobnostní distribučni funkci koncentrací pasivní příměsi
Jurčáková, Klára ; Riveron, F.
The scope of this study is to find general description of probability distribution functions (PDF), which describes temporal variation of passive contaminant concentrations released from ground level point source within the atmospheric boundary layer. The Weibull distribution was found to be most suitable form for those PDFs. Two parameters of Weibull distribution were found to be a function of gross time series parameters such mean and standard deviation values of the concentration time series.
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Numerické řešení 2D proudění v atmosférické mezní vrstvě
Šimonek, J. ; Tauer, J. ; Kozel, K. ; Jaňour, Zbyněk ; Příhoda, Jaromír
The work deals with the numerical solution of the 2D incompressible laminar flow over the profile DCA 10% for Reynolds numbers 10^5 and 10^6 and with the stratified flow in the atmospheric boundary layer over the sinus hill for Reynolds numbers 10^8 and 5x10^8. The mathematical model for the 2D laminar flow is formed by the Navier-Stokes equations for incompressible fluid. The averaged Navier-Stokes equations for incompressible turbulent flow with addition of the equation of density change (Boussinesq model) were used as a mathematical model for stratified flow in ABL. Turbulent flow was modelled by means of the algebraic turbulence model.
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Numerická simulace mezní vrstvy atmosféry
Bauer, Petr
We develop a mathematical model based on Navier-Stokes equations for viscous incompressible flow and diffusion-convection equation describing pollution transport, and solve the model using finite element method (FEM). We use a simple algebraic model with turbulent viscosity. The FEM allows us to use different terrain shapes and study their influence. Essential part of the work is numerical analysis, which examines the properties of algorithms with respect to numerical parameters. We present the recent results of flow over a square gap.
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