0458435 - ÚT 2017 RIV FR eng J - Journal Article
Nosek, Štěpán - Kellnerová, Radka - Jurčáková, Klára - Jaňour, Zbyněk - Chaloupecká, Hana - Jakubcová, Michala
Effect of shelter porosity on downwind flow characteristics.
EPJ Web of Conferences. Roč. 114, March (2016), 02084-02084. ISSN 2100-014X.
[Experimental Fluid Mechanics 2015 /10./. Praha, 17.11.2015-20.11.2015]
R&D Projects: GA ČR GA15-18964S
Institutional support: RVO:61388998
Keywords : atmospehric boundary layer * porosity * coherent structures * wind tunnel
Subject RIV: BK - Fluid Dynamics

Previous wind-tunnel studies were focused mainly on lonely standing windbreaks or wind fences with respect to their wind velocity reduction efficiency and effective shelter distance. In presented wind-tunnel study, we investigated the effects of a three different fence porosities (0.5, 0.25 and 0) embodied in a shelter-like building for coal convey by means of two-component Laser Doppler Anemometry (LDA). The turbulent flow characteristics behind the fences were compared with those performed without the fence. For characterization of the fence effectiveness we used following quantities: wind-speed and turbulence kinetic energy reduction, and time fractions of the turbulent coherent structures associated with the sediment transport (sweeps and outward interactions). Results from mentioned quantities revealed that for the case of embodied fence the shelter construction has significant impact on the flow characteristics behind. The fence of the 0.5 porosity has been indicated as the most shelter effective considering the studied quantities.
Permanent Link: http://hdl.handle.net/11104/0262206

 

0483047 - ÚT 2018 RIV GB eng J - Journal Article
Chaloupecká, Hana - Jaňour, Zbyněk - Mikšovský, J. - Jurčáková, Klára - Kellnerová, Radka
Evaluation of a new method for puff arrival time as assessed through wind tunnel modelling.
Process Safety and Environmental Protection. Roč. 111, October (2017), s. 194-210. ISSN 0957-5820. E-ISSN 1744-3598
R&D Projects: GA ČR GA15-18964S
Institutional support: RVO:61388998
Keywords : wind tunnel * short-term gas leakage * puff
OECD category: Meteorology and atmospheric sciences
Impact factor: 3.441, year: 2017
https://www.sciencedirect.com/science/article/pii/S0957582017302203

Deliberate or accidental gas leakages threaten people′s lives. Short-duration releases of gas are influenced by actual phase of turbulent atmospheric flow and therefore the study of these situations requires multiple repetitions of the leakage under the same mean conditions. Such a set of experiments was conducted in a wind tunnel on a scaled model of an idealized urban canopy created by rectangular buildings with pitched roofs organized into closed courtyards. Concentration time series of high time resolution were measured by a fast flame ionisation detector. The arrival time of gas from short-duration discharges was investigated at a few places of detection. This paper introduces a new method of defining gas arrival time, one not only applicable in the post-processing analysis but also in the operative stage. Moreover, it shows the results of other commonly used gas arrival time definitions (visual and dosage methods and a method utilizing the maximum detected concentration). It was explored both, the change in the arrival time value in individual realisations and places as well as the change in statistical values calculated from ensembles (mean, median, quartiles). Furthermore, the dependence of the definitions of arrival time on their parameters is discussed.
Permanent Link: http://hdl.handle.net/11104/0278503

 

0376477 - ÚT 2013 RIV GB eng J - Journal Article
Kellnerová, Radka - Jaňour, Zbyněk
Flow instabilities within an urban intersection.
International Journal of Environment and Pollution. Roč. 47, 1-4 (2011), s. 268-277. ISSN 0957-4352. E-ISSN 1741-5101
Institutional research plan: CEZ:AV0Z20760514
Keywords : wind-tunnel * street canyon * flow instability * urban intersection * environmental pollution * quadrant analysis
Subject RIV: DG - Athmosphere Sciences, Meteorology
Impact factor: 0.361, year: 2011
http://inderscience.metapress.com/content/e301241p70566w5w/

Turbulent flow inside street canyons was studied using Laser Doppler Velocimetry (LDV) in wind-tunnel experiment. Spatial distribution of momentum flux and moments of third and fourth order of velocity components obtained from one-point measurement are investigated. The area of interest covers an inner part of street canyon and adjacent intersection. Time-averaged momentum flux is divided into particular quadrants using Quadrant Analysis method. Comparison between flux events and skewness provides some insight into the spatial distribution of strong intermittent tendency. Therefore, we can explain better the spatially local dominance of sweep, respectively ejection that corresponds to intermittent gust moving inward, respectively outward from canyon.
Permanent Link: http://hdl.handle.net/11104/0208863

 

0476809 - ÚT 2018 RIV GB eng J - Journal Article
Nosek, Štěpán - Kukačka, L. - Jurčáková, Klára - Kellnerová, Radka - Jaňour, Zbyněk
Impact of roof height non-uniformity on pollutant transport between a street canyon and intersectionsle.
Environmental Pollution. Roč. 227, August (2017), s. 125-138. ISSN 0269-7491. E-ISSN 1873-6424
R&D Projects: GA ČR GA15-18964S
Institutional support: RVO:61388998
Keywords : Urban array * 3D street canyon * pollution flux measurement * wind tunnel * coherent structures
OECD category: Meteorology and atmospheric sciences
Impact factor: 4.358, year: 2017

This paper presents an extension of our previous wind-tunnel study (Nosek et al., 2016) in which we highlighted, the need for investigation of the removal mechanisms of traffic pollution from all openings of a 3D street canyon. The extension represents the pollution flux (turbulent and advective) measurements at the lateral openings of three different 3D street canyons for the winds perpendicular and oblique to the along-canyon axis. The pollution was simulated by emitting a passive gas (ethane) from a homogeneous ground-level line source positioned along the centreline of the investigated street canyons. The street canyons were formed by courtyard-type buildings of two different regular urban-array models. The first model has a uniform building roof height, while the second model has a non-uniform roof height along each building's wall. The mean flow and concentration fields at the canyons' lateral openings confirm the findings of other studies that the buildings' roof-height variability at the intersections plays an important role in the dispersion of the traffic pollutants within the canyons. For the perpendicular wind, the non-uniform roof-height canyon appreciably removes or entrains the pollutant through its lateral openings, contrary to the uniform canyon, where the pollutant was removed primarily through the top. The analysis of the turbulent mass transport revealed that the coherent flow structures of the lateral momentum transport correlate with the ventilation processes at the lateral openings of all studied canyons. These flow structures coincide at the same areas and hence simultaneously transport the pollutant in opposite directions.
Permanent Link: http://hdl.handle.net/11104/0273575

 

0341758 - ÚT 2010 RIV GB eng J - Journal Article
Yassin, M.F. - Kellnerová, Radka - Jaňour, Zbyněk
Impact of street intersections on air quality in an urban environment.
[Vliv křižovatky na kvalitu ovzduší v městském prostředí.]
Atmospheric Environment. Roč. 42, č. 20 (2008), s. 4948-4963. ISSN 1352-2310. E-ISSN 1873-2844
R&D Projects: GA MŠMT(CZ) OC 113
Keywords : atmospheric turbulence * CFD model * pollutant dispersion * street cynyon
Subject RIV: BK - Fluid Dynamics
Impact factor: 2.890, year: 2008

The concentration fields in the urban canyons were examined in three street configurations cases: (i) a regular-shaped intersection, (ii) T-shaped intersection and (iii) skew-shaped crossing intersection. Standard "k-epsilon" turbulence model and CFD FLUENT code has been used and the numerical model was validated against wind tunnel results in order to optimalize the turbulence model

Pole koncentrací uvnitř uličního kaňonu bylo zkoumáno pro tři různé konfigurace: (i) pravidelnou křižovatku, (ii) křižovatku ve tvaru T,(iii) křižovatku šikmou. Standartní "K-epsilon" model turbulwence je použit společně s CFD řešičem FLUENT a numerický model byl validován na datech z tunelových měření s cílem optimalizovat model turbulence
Permanent Link: http://hdl.handle.net/11104/0184644