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Core of emergency model for urban canopy & Experiments of gas leakages for rural area
Chaloupecká, Hana ; Jakubcová, Michala ; Kellnerová, Radka ; Jurčáková, Klára
The report consists of two parts.\nThe first part copes with the development of an emergency model core for short-term gas leakages for urban canopy. It is explained a procedure in the development of the model, in which after recording input data describing a gas leakage as an output probability density functions for individual puff characteristics and exposed places are obtained. From the output, one can see for example the most probable puff characteristics, which can occur during an accident as well as extreme cases. This is the biggest difference in comparison with the usually used emergency models, in which only mean puff contours and concentration fields are the output. \nIn the second part, experiments of gas leakages for rural area are described. Fulfilment of similarity criterions in wind-tunnel modelling as well as the experiments themselves and the database development is showed.\n
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Spatial and temporal correlations in turbulent boundary layers
Jurčáková, Klára ; Kellnerová, Radka
The experimental data from time-resolved particle image velocimetry measurement of the boundary-layer flows over various aerodynamically rough surfaces are presented. Temporal, spatial, and time-space correlation are analyzed and used for calculation of integral length and time scales. Temporal and spatial integral scales are connected via convection velocity. Taylor's hypothesis on frozen turbulence says that the convection velocity is equal to the local mean velocity. The experimental data shows that the convection velocity is larger than local mean velocity in the lower third of the boundary layer and greater in the upper two thirds. The cross-over line is higher over surfaces with higher roughness.
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Impact of Turbulence Generators on Turbulent Characteristics and Structures
Kellnerová, Radka ; Jurčáková, Klára ; Jaňour, Zbyněk
The turbulent generators are routinely used to produce very turbulent flows. Special type of vertically slenderize spires are applied to enhance turbulent diffusion from the surface upwards in order to increase the boundary layer depth. This paper studies the influence of variable upstream distance of generators on formation of both vortical and non-vortical organized structures within a test section. The 2-component 2-dimensional time-resolved particle image velocimetry measurement of the flow was performed in the wind channel with very rough surface. Intermittent flow dynamics was evaluated by means of higher order moments, vorticity, quadrant and wavelet analysis. The downstream evolution of the flow suggests that equilibrium between roughness- and spires-produced turbulence was reached at the distance of 7 spires height.\n
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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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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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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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Wind tunnel study of dispersion in different urban area configurations
Chaloupecká, Hana ; Jurčáková, Klára ; Kellnerová, Radka ; Kukačka, Libor ; Jaňour, Zbyněk
The object of this study is modelling of pollution dispersion in a wind tunnel. We’ve used the inverse method of modelling to this.That means a given location of detector of pollution and a net of points where we placed one by one a point source. We’ve studied this probem for different set-ups of buildings and approach flow directions. A sensitivity of concentration diffusion upon on the type of set-up of buildings and approach flow direction has been demonstrated from the results of experiment. The best se-up of buildings due to the measurement of concentration in two fixed points has been found.
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