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Dynamika proudění uvnitř městské křižovatky: charakteristiky šikmosti a špičatosti
Kellnerová, Radka ; Jaňour, Zbyněk
The experiment uses wind-tunnel modeling method to investigate an intermittent ventilation of pollutants within an urban intersection and adjacent canyon. The skewness and kurtosis of velocity components were obtained in order to identify an area with strong intermittent tendency. Pollutants have released from line source and mean concentration was obtained using slow flame ionization detector. Vertical vortices as well as corner vortices are responsible for accumulation of emissions emitted by vehicle traffic. However, flow instabilities corresponding to enhancement of skewness can reduce or enhance the instantaneous level of exhalations. Vertical and horizontal momentum flux was analyzed by quadrant analysis. The method has detected the localities with highest momentum transfer from free stream down to the canyon. The connection between sweep and skewness in this area was found.
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Vlastnosti trysek – experimentální ověření na zažízení stavěném pro výzkum šroubovicových nestabilit
Tesař, Václav ; Kellnerová, Radka ; Kukačka, Libor ; Kordík, Jozef
Nozzle characterisations in current use may be described as zero-order (neglected loss) and first-order (constant loss coefficient). The first author (V. Tesar) introduced in 1985 a second-order theory, fully predicting all the variations of nozzle properties with Reynolds number Re. The basic idea is an assumption of the loss being entirely specified by displacement effect of wall boundary layer in the exit. The other assumption is the layer thickness being governed by laminar boundary layer growth law. All evidence for this theory so far was only indirect. This paper presents recent direct experimental verification by measurements of boundary layer profiles on a large-scale nozzle model across a wide range of Re. The predictions of the 1985 model are fully supported.
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Turbulentní charakteristika uvnitř městské křižovatky
Kellnerová, Radka ; Jaňour, Zbyněk
The wind-tunnel experiment checked the central symmetry for the inlet conditions and the flow inside an one case of symmetric model. For approaching flow, central asymmetry of y- and z-component of velocity between the right and left side of tube was detected. Nonetheless, the model of urban intersection has a dominant role in flow up to the 1.5 height of building and just mild asymmetry was found here. For elimination of these discrepancies the influence of wind direction and model arrangement suppressing the lateral flow was tested. The main reason for asymmetry was appeared to be a position of the mounted probe of LDA measuring facility. The turbulent characteristics obtained inside the model were analysed using Quadrant analysis technique. This helped to understand the structure of momentum flux in lower surface layer called the roughness sublayer.
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Symetrie turbulentních charakteristik uvnitř městské křižovatky
Kellnerová, Radka ; Jaňour, Zbyněk
The wind-tunnel modelling of dispersion is very sensitive to central symmetry. The asymmetry of concentration field inside the symmetrical model is often caused by two causes: inappropriate inlet conditions or non-symmetric set-up of model. The project has carried out the flow measurements by Laser Doppler Anemometer's probe merged into the tunnel. The aim was to investigate the flow processes inside the tunnel body-tube itself – i.e. without the model and inside the model of a symmetrical urban intersection. The influence of wind direction and model arrangement suppressing the lateral flow was tested. The largest deviations from symmetry were caused by the circumfluence of the measuring devices.
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Pole rychlosti a koncentrace v oblasti křižovatky
Kellnerová, Radka ; Jaňour, Zbyněk
The aim of this project is to investigate the influence of intersection configuration on spreading of contaminants from the vehicle traffic. Experiment was performed by physical modeling method. For crossroad in the shape of perpendicular X, we have measured the mean velocity and concentration field. The flow investigation has confirmed that within the area of corner vortexes occurs to the largest accumulation. Further in the canyon the concentration field is affected by developed vertical vortex and accumulation appears mostly on the leeward side.
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Vyšetřování charakteristik ventilátoru použitého jako zdroj vzduchu v experimentálním zařízení pro zkoumání šroubovicových nestabilit v proudících tekutinách
Tesař, Václav ; Kukačka, Libor ; Kellnerová, Radka
For investigations of aerodynamic properties of helical instabilities in flowing fluids, an experimental rig is currently built. It is intended on the one hand for visualisations of acoustically excited helical structures and on the other hand for model experiments with flows of cyclonal character. As the universal air source for both purposes, a blower is used for which no loading characteristics were available - and which, at any rate, is to be operated in some of the regimes at very low Reynolds numbers where one has to expect deviation from characteristics obtained under standard conditions. The authors investigated the blower loading characteristics experimentally and used this opportunity to apply and test practical validity of the general ideas about universal representation of characteristics and criterial similarity parameters of turbomachines, published considerable time ago but seemingly little known and used.
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Study of velocity field in crossroads areas
Kellnerová, Radka ; Jaňour, Zbyněk
The aim of this project is to study the influence of boundary conditions on contaminant spreading in a urban area model. The urban area model was composed of simple elements shapes of crossroads: X-shaped, T-shaped and skew intersection. The project at the beginning - by now only results for T-shaped crossroads are available. The experiment took place in an environmental aerodynamics tunnel IT AS CR in Nový Knín. First results show accumulation of high values of Reynolds stress above the area of crossroads center, whereas the velocity field is weaker when compared with more remote area. In specific distance from the intersection the recirculating zone appears. With increasing distance from intersection the center of zone moves counter main flow and up.
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Modelování úniku a disperze nebezpečného plynu
Jaňour, Zbyněk ; Bezpalcová, Klára ; Erhart, Jakub ; Kellnerová, Radka ; Šeděnková, Hana
Liquefied industrial gases and liquefied energy gases are transported, stored and used in steadily increasing amounts.Since the vapours of many of these chemicals are either toxic or flammable or both, there is heightened concern amongst public and regulatory bodies on potential hazards in a case of accidental releases. The objective of this contribution is to present the concept and result of a wind tunnel study of the dispersion of pollution clouds in a atmospheric boundary layer. Scaling laws, which have to be fulfilled in order to ensure model/prototype similitary, have been developed. Examples of the method application have been demonstrated.
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Wind tunnel concentration field study in a urban area
Jaňour, Zbyněk ; Kellnerová, Radka ; Bezpalcová, Klára
The aim of the project was to study the influence of boundary conditions on contaminant spreading in a urban area model. The experiment was conducted a low-speed open-circuit tunnel. The urban area model was scaled down to 1:200. The model aimed to simulate a typical street with intense traffic, in our case specifically the Podbielski Strasse in Hannover (Germany). The downstreet flow was at an aproximate angle of 45 degrees to the street axis. Traffic was simulated by a double-line source. In the course of the experiment we have replaced a convoluted model of a park in the upstream area with simpler elements of varying size and density. We then compared the concentration field of the new arrangement with the original concentration field. All configurations led to a decrease of concentration . In ares where the original concentration had reached the highest values, the most significant decrease was obtained.
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