Urban Large-Eddy Simulation

Video in TIB AV-Portal: Urban Large-Eddy Simulation

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Urban Large-Eddy Simulation
Influence of a densely build-up artificial island on the turbulent flow in the city of Macau
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Silent film
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The animation displays the development of turbulence structures induced by a densely built-up artificial island off the coast of Macau. Animation data were derived using the parallelized large-eddy simulation model PALM (http://palm.muk.uni-hannover.de/), simulating a neutrally stratified flow over Macau, with a mean flow from the southeast to the northwest and a 10-m wind of approximately 1m/s. The vertical direction of the model domain is stretched by a factor of 3 for better visualization. Turbulence structures and intensities are visualized by the rotation of the velocity vector (absolute values), with highest values in red and lowest values in white. Buildings are displayed in blue. The animation spans over 1 hour with a time-lapse factor of 43, and was created with the visualization software VAPOR (www.vapor.ucar.edu). The total PALM model domain had a size of 768 x 256 x 96 grid points in streamwise, spanwise and vertical direction, with a uniform grid spacing of 8m in each direction. Above 400m the vertical grid spacing is successively stretched up to a maximum vertical grid spacing of 40m. Non-cyclic boundary conditions are used in streamwise direction and a turbulence recycling method is applied, in order to guarantee a fully turbulent inflow. In total, the simulation required 1 hour of CPU time using 128 cores on the Cray-XC30 of the North-German Supercomputing Alliance (https://www.hlrn.de/). The approaching flow above the sea shows a comparatively low turbulence intensity due to the smooth water surface. Within the building areas, strong turbulence is generated by two main reasons. One is the additional wind shear due to the walls of isolated highrise buildings. Furthermore, due to the significant increase in surface roughness, a so called internal boundary layer with enhanced turbulence develops above the building areas. The depth of this layer grows in downstream direction. During the animation the camera moves through three major viewing angles. The first part of the animation starts with an aerial view onto the whole Macau area. Afterwards the camera zooms in, displaying those areas of the model domain, in which the flow field is particularly influenced by buildings. The second part is a side view from close above the surface and shows the above mentioned internal boundary layer. The last part shows another aerial view focusing on the gap between the artificial island and the Macau Peninsula, where turbulence decreases as it is advected across the gap.
Keywords large-eddy simulation internal boundary layer urban canopy städtische Grenzschicht PALM
Computer animation
Computer animation
Computer animation
Computer animation
Computer animation