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Wind-tunnel Modelling of Turbulent Flow Inside the Street Canyon
Kellnerová, Radka ; Jaňour, Zbyněk (advisor) ; Brechler, Josef (referee) ; Jonáš, Pavel (referee)
Turbulent flow inside a street canyon was investigated in an open circuit wind tunnel and in a blow-down wind channel. Two geometries were used for comparison purposes: buildings with pitched roofs and with flat roofs. Both generate the flow of a different category, so the induced ventilation regimes are fundamentally different. Quadrant, Fourier and Wavelet analysis, Proper Orthogonal Decomposition (POD) and vortex detection methods are used to identify coherent structures in the flow and establish their impact on the ventilation of pollution. Two types of the organised motions are detected: the compact areas of sweep and ejection with the scale comparable to the size of building and the small vortices generated in the shear layer behind the building roof. POD identifies the most dominant modes with high coherency in the flow and evaluates the relative contributions of each mode to the overall kinetic energy of turbulence. Rigorous analysis of the correctness of the physical interpretation for such a decomposition is carried out. Wavelet analysis is applied to the time-series of the POD expansion coefficients in order to reveal control mechanism of the dynamics of the modes. Vorticity, calculated from the original velocity data, is decomposed by POD as well. Finally, the correlation between the vorticity...
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Mathematical modelling of air-flow in geometrically complicated areas
Fuka, Vladimír ; Brechler, Josef (advisor) ; Fürst, Jiří (referee) ; Jaňour, Zbyněk (referee)
The Charles University Large-eddy Microscale Model (CLMM) and its application are presented. It is a numerical model for simulation of turbulent flow and dispersion in the planetary boundary layer. CLMM solves the incompressible Navier-Stokes equations in the Boussinesq approximation and describes turbulence using the large eddy simulation. Three applications of the model are presented. In the first case, the model is applied to the stable boundary layer over a flat terrain. The second case presents the simulations of stably stratified flows over obstacles. The last case deals with the dispersion of a hazardous material within an urban canopy. It was performed in the frame of the COST Action ES1006 and uses the Michelstadt flow and dispersion dataset for model validation.
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Flow and diffusion characteristics inside the urban area
Chaloupecká, Hana ; Jaňour, Zbyněk (advisor) ; Brechler, Josef (referee)
Title: Flow and diffusion characteristics inside the urban area Author: Hana Chaloupecká Department: Department of meteorology and enviroment protection Supervisor: prof. RNDr. Zbyněk Jaňour, DrSc., IT AS CR, v. v. i. Supervisor's e - mail: janour@it.cas.cz Abstract: Uniqueness of different towns, consists of various shapes of buildings. The main topic of this work is to compare concentration diffusion within groups of buildings of various types. We pursued houses made of single blocks of two different lengths - they were placed parallel or in courtyards. For research of pollution diffusion within the housing estates a method of physical modelling has been used. For this purpose we summarized a theory of atmospheric boundary layer and physical modelling at first. Then we pursued experiments. Measuring took place in a model in scale 1 : 300 inside an aerodynamic wind tunnel of the Institute of Thermomechanics AS in Nový Knín. We checked out the requirements placed on similarity of the real boundary layer and boundary layer modelled in the tunnel. By the measuring of concentration in urban areas we weren't watching a plume from the pollution source but we were studying an inversion task. We measured concentrations in two fixed points from different point sources inside the defined areas. A sensitivity of...
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Thermally stratified atmospheric flow modelling
Jirk, Aleš ; Brechler, Josef (advisor) ; Jaňour, Zbyněk (referee)
In this thesis there is simulated an incompressible laminar flow in a higher-order accuracy around a circle cylinder with usage of an immersed boundary method and around a cylinder with a square cross-section with an influence of a thermal stratification. In the theoretical part the system of Navier-Stokes equations with Bussinesq approximation is derived and the methods for simulating are described. Fifth order WENO shock-capturing scheme reconstructs advections terms on the boundaries of control volumes. An explicit fourth-order Runge-Kutta scheme solves the first step of a fractional steps method. The obstacle with the circle cross-section is described by the immersed boundary method. In the implementation section there is interpreted the structure of programs for 2D cases. In the section Numerical experiments there is realized testing of the examples with the exactknown results the linear hyperbolic equations, the Burgers equations and the Euler equations and of a square cavity flow with Reynolds numbers of 100,1000 and 5000 with known numerical results for the Navier-Stokes equation. There is solved the flow around a square (and a circle) cylinder for Reynolds numbers 30; 200. Strouhal numbers are computed for von Kármán vortex street. Finally the flow around a square cylinder with influence of thermal...
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Microscale flow and diffusion characteristics inside the urban area
Kukačka, Libor ; Brechler, Josef (referee) ; Jaňour, Zbyněk (advisor)
Dispersion of pollutants in the atmosphere of urban areas is the important task in environmental sciences. The main goal was the quantitative studying of a flow in a symmetrical urban built-up area depending on a running on flow direction. There was given a theoretical base of the physical modeling of the atmospheric boundary layer in this work. The measurement was done with a model of the urban build-up area at a scale of 1:200 in the aerodynamic wind tunnel of the IT AS CR, v.v.i. in Nový Knín. The requirements to the similarity to a real atmospheric boundary layer and a model boundary layer in the wind tunnel were accomplished. Velocity fields, concentration fields and fields of scalar uxes were measured in the area of a rectangular intersection. Results of the experiment showed significant sensitivity of the velocity field about the running on flow direction that extensively inuenced ventilation of street canyons.
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Air Qaulity at Pedestrian Zone: The Role of Urban-Array Three-Dimensionality
Nosek, Štěpán ; Kellnerová, Radka ; Chaloupecká, Hana ; Jakubcová, Michala ; Jaňour, Zbyněk
Air quality at pedestrian level of two different urban arrays for two wind directions was studied experimentally in a wind-tunnel. Both urban arrays were designed according to typical European cities, formed by courtyard-type buildings with pitched roofs. While the first urban array had constant roof height, the second had variable roof height along all walls. The pollution was simulated by means of ground-level line source in the middle of the urban arrays. The concentrations were measured by a flame ionization detector at horizontal planes at the pedestrian level within the streets and courtyards at the vicinity of the line source. Results of the time and spatial averaged concentration reveal that both wind direction and three-dimensionality of the urban morphology are important parameters influencing the air quality at the pedestrian zones within the urban areas.
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