Urban Pollution Dispersion

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Video in TIB AV-Portal: Urban Pollution Dispersion

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Urban Pollution Dispersion
Large-eddy simulation of a heavy atmospheric pollution release event in an urban environment
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Silent film
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The animation displays the dispersion of a pollutant released in the city center of Hannover, Germany. Data were derived using the large-eddy simulation model PALM (https://palm.muk.uni-hannover.de), simulating a neutrally stratified atmosphere and a north-westerly wind of 5 m/s. Pollutant is released constantly near the ground at the Steintorplatz and is advected with the mean flow trough the city center. Red color represents areas with high concentration while yellow color marks low concentration. The model domain spans over an area of 744 by 504 by 72 grid points in stream-wise, span-wise and vertical direction, respectively, with a grid resolution of 2 m in each direction. For the wind field, cyclic boundary conditions are used in lateral direction, while a Neumann condition is used for the pollutant in lateral direction and at the top. The animation spans over 40 minutes with a time-lapse rate of 24. The simulation required 1.5 hour of computing time on 576 cores on the Cray-XC40 of the North-German Supercomputing Alliance (www.hlrn.de). VAPOR (www.vapor.ucar.edu) was used to generate the images. The animation is divided in three parts. The first part gives an overview of the pollutant concentration by showing the pollutant cloud from different angles. For the second part, concentration is displayed only below 10m height to show the advection through the streets. Additionally, three time series display the concentration at different positions within the streets. In the end, the mean concentration is displayed. The left-most measurement position is situated at a small square. Concentration at this point is rather low with some prominent peaks around minute 6, 9, and 17 due to turbulent motion. The bottom measurement shows the largest concentration as it is positioned directly downwind of the pollutant source. Due to turbulence, the variation of concentration is high as well. The right-most measurement appears to give only small variation. However, at minute 10, concentration increases significantly and stays on a high level during the following 10 minutes. In comparison to the mean concentration (red line displayed together with the time series at the end of the animation), all three measurements reveal that the mean concentration does hardly represent the actual concentration at any given time underlying the importance of turbulence for pollutant dispersion. The animation was created as part of the MOSAIK project funded by the German Federal Ministry of Education and Research (BMBF) under grant 01LP1601A within the framework of Research for Sustainable Development (FONA; www.fona.de).
Keywords large-eddy simulation turbulent boundary layer urban pollution dispersion PALM High-Performance-Computing