|
|
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...
|
|
|
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...
|
|
|
Identification of coherence in turbulent flows by local correlations
Tesař, Václav ; Něnička, Václav
Coherent structures are not included in practically useful models of turbulence due to scarcity of data upon which the modelling could be based. The problem is indistinct, vague, and continuously varying boundary of each structure, making difficult even identification of its very existence. The introduced identification method operates with a pair of flow visualisation images, computing local correlation coefficients in sequentially interrogated small image parts. The coherence is revealed by high local values of the coefficient. There are two variants, a scalar and vector approaches. The method is shown applied to an experiment in which the structures play an important role.
|
|
|
Detailed analysis of POD method applied on turbulent flow
Kellnerová, Radka ; Kukačka, Libor ; Uruba, Václav ; Jurčáková, Klára ; Jaňour, Zbyněk
Proper orthogonal decomposition (POD) on very turbulent flow inside the street canyon is performed. The energy contribution of each mode is yielded up. Also, physical meaning of the POD method is clarified. Particular modes of POD are assigned to the particular flow events like sweep event, vortex behind the roof or vor- tex at the bottom of street. Test of POD sensitivity on the length of data recording is done when the acquisition time increases up to its triple value. Test with decreasing sample frequency is executed. Further, interpola- tion of POD expansion coefficient is attempted in order to test possible increase in sample frequency and get new information about flow from the POD analysis. We tested linear and spline sort of interpolation and the linear one brought slightly better results.
|
|
|
Struktury vyvolané nestabilitou v impaktním proudění
Tesař, Václav ; Něnička, Václav
Authors investigated by flow visualisation an air jet impinging on a perpendicular flat plate. The jet was supplied with tiny water droplets, produced by condensation, which caused scattering of laser light illuminating the section of the jet in meridian plane. A high-speed camera, operating in an adjustable phase relationship with acoustic signals triggering the formation of the instabilities was used to record the visualisation images. These were then processed using advanced procedures aimed at identifying the structures.
|
|
|
Analysis of turbulent flow over forested terrain
Potužníková, Kateřina ; Sedlák, Pavel ; Šauli, Petra
The aim of the present study is to assess and describe low-frequency oscillations and coherent structures in temporal series of temperature and wind velocity components sampled at three different levels within the forest (z/h = 0.3, 0.5 and 1, where h is the canopy height). The wavelet transform is used as a basic tool for our analysis. The periods of detected structures depend on the temperature gradient in the canopy, and furthermore seem to vary with the different local circulations regimes.
|
|
| |
|
| |
|
| |
guest ::
