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01:44 Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie Silent film 2015

Non-Cyclic Turbulent Inflow

The animation shows a comparison between two large-eddy simulations (LES) using different inflow boundary conditions. For both simulations the LES model PALM was used, simulating a neutral stratified flow over an array of building cubes. The upper half of this visualization shows a simulation, which uses a laminar inflow at the left boundary while the lower half shows a simulation, which uses a turbulence generator based on a filter method at the left boundary. The size of both domains is 2180m x 720m x 240m with a mean background wind of 6 m/s at the top of the domain blowing from left to right. The rotation of the velocity vector (absolute values) is visualized to show the turbulence structures and intensities. High values are marked red while low values are white. The buildings have a cubic shape with 24m edge length and are packed with a plane area index of 0.25. One tall building sits in the center of the domain with three times the size of a small building in horizontal direction and four times the size in vertical direction. The animation was created using the visualization software VAPOR. Simulations were calculated on the Cray-XC30 of the North-German Supercomputing Alliance as well as on the TSUBAME 2.5 of the Tokyo Institute of Technology. In the simulation with laminar inflow (top), first turbulent motions can be spotted behind the tenth building row. In reality such a laminar flow is almost never observed and hence very artificial. In the simulation with generated turbulent inflow (bottom), turbulence is created at the inflow boundary. This leads to an already turbulent flow above the first building rows. This flow is much more realistic. The flow in close vicinity to the tall building at the center of the domain shows slight differences between the two simulations. These differences can especially be seen at the rooftop of the tall building. Here the arriving flow in the top simulation shows almost no developed turbulence, while the arriving flow in the bottom simulation is already turbulent. At the outflow boundary however, both simulations show nearly equally developed turbulence. The results indicate, that the used turbulence generation method allows legitimate analysis of simulation data much closer to the inflow boundary which can result in significant cost savings due to smaller required domain sizes.
  • Published: 2015
  • Publisher: Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie
  • Language: Silent film
02:40 Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie Silent film 2015

Airport Area Large-Eddy Simulation

The animation displays the influence of airport-building induced turbulence on an aircraft during a crosswind landing. The animation data were derived using the parallelized large-eddy simulation model PALM, simulating a neutrally stratified flow over an artificial building, with a mean flow from the west (perpendicular to the obstacle and the runway) and a free stream wind of 20 m/s. Visualized is the crosswind variation as difference between the instantaneous and the mean wind field, with positive values in red and negative values in blue. The building is 25 x 250 x 40 m³ (length x width x height) and displayed in white. The animation spans over 9 minutes with parts accelerated by a time-lapse factor of 5, and was created with the visualization software VAPOR. The total PALM model domain had a size of 4 x 2 x 2 km³ in streamwise, spanwise and vertical direction. The displayed domain extends over 500 x 1000 x 200 m³. During the last 20 seconds of the simulation, the crosswind variation encountered by the aircraft during its final approach is tracked and dispalyed on the flightpath of the aircraft as well as in a temporal history plot in the lower left corner of the screen. The aircraft has a ground speed of 70 m/s. Its flightpath is 450 m downstream from the building. The airport building generates strong turbulence with resulting crosswind variations of up to 10 m/s. The aircraft encounters these strong crosswind variations within a few seconds. During the flight, the crosswind drops from more than 15 m/s down to almost 0 m/s. The animation can be divided into two major parts. The pre-flight part of the animation starts with an aerial view onto the entire airport area and shows several perspectives of the scene with slow camera moves. The flight part shows the final approach of the aircraft.
  • Published: 2015
  • Publisher: Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie
  • Language: Silent film
02:14 Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie Silent film 2014

Urban Large-Eddy Simulation

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.
  • Published: 2014
  • Publisher: Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie
  • Language: Silent film
01:29 Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie Silent film 2014

Large-eddy simulation of a forest-edge flow

The animation displays the development of coherent turbulent structures above a forest canopy downstream of a clearing-to-forest transition. Animation data were derived using the parallelized large-eddy simulation model PALM (http://palm.muk.uni-hannover.de/), simulating a neutrally stratified forest-edge-flow with a mean flow from left to right and a 10-m wind of 6m/s above the clearing. The forest, as surrounded by the green isosurface, is modeled in PALM as a porous viscous medium that decelerates the mean flow and damps the turbulence. Only a part of the total PALM domain is presented, and the vertical direction is stretched by a factor of 1.5 for better visualization. Turbulence structures and intensities are visualized by the rotation of the velocity vector (absolute value), with highest values in pink and lowest values in yellow. The animation spans over the last 180 seconds of a 3-hr simulation with a time-lapse factor of 3.6, and it was created with VAPOR (www.vapor.ucar.edu). The total PALM domain had a size of 768 x 384 x 128 grid points in streamwise, spanwise and vertical direction, with a uniform grid spacing of 3m in each direction. In total, the simulation required 18 hours of CPU time using 512 CPUs on the SGI Altix ICE of the North-German Supercomputing Alliance (https://www.hlrn.de/). The approaching flow is turbulent with different scales of turbulence being randomly distributed. Entering the forest volume, turbulence is efficiently damped by the forest drag. Above the forest, turbulence is effectively generated due to the strong velocity shear near the forest top. With increasing distance from the forest edge, the developing turbulence structures grow in size and strength. They form a layer of high turbulence activity, a so-called internal boundary layer, within the flow adjusts to the abrupt change of the surface conditions at the clearing-to-forest transition.
  • Published: 2014
  • Publisher: Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie
  • Language: Silent film
01:29 Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie Silent film 2014

Large-eddy simulation of the scalar transport in a forest-edge flow

The animation displays the development of coherent turbulent structures above a forest canopy downstream of a clearing-to-forest transition. Animation data were derived using the parallelized large-eddy simulation model PALM , simulating a neutrally stratified forest-edge-flow with a mean flow from left to right and a 10-m wind of 6m/s above the clearing. The forest, as surrounded by the green isosurface, is modeled in PALM as a porous viscous medium that decelerates the mean flow and damps the turbulence. Only a part of the total PALM domain is presented, and the vertical direction is stretched by a factor of 1.5 for better visualization. Turbulence structures and intensities are visualized by the rotation of the velocity vector (absolute value), with highest values in pink and lowest values in yellow. The animation spans over the last 180 seconds of a 3-hr simulation with a time-lapse factor of 3.6, and it was created with VAPOR (www.vapor.ucar.edu). The total PALM domain had a size of 768 x 384 x 128 grid points in streamwise, spanwise and vertical direction, with a uniform grid spacing of 3m in each direction. In total, the simulation required 18 hours of CPU time using 512 CPUs on the SGI Altix ICE of the North-German Supercomputing Alliance. The approaching flow is turbulent with different scales of turbulence being randomly distributed. Entering the forest volume, turbulence is efficiently damped by the forest drag. Above the forest, turbulence is effectively generated due to the strong velocity shear near the forest top. With increasing distance from the forest edge, the developing turbulence structures grow in size and strength. They form a layer of high turbulence activity, a so-called internal boundary layer, within the flow adjusts to the abrupt change of the surface conditions at the clearing-to-forest transition.
  • Published: 2014
  • Publisher: Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie
  • Language: Silent film
00:40 Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie Silent film 2013

Large-eddy simulation of dust devils

This animation shows the development of dust dvils in the convective boundary layer. The dust devils are visualized by virtual dust that is released at the surface of the model. Rendering is done using VAPOR
  • Published: 2013
  • Publisher: Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie
  • Language: Silent film
02:50 Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie Silent film 2017

Urban Pollution Dispersion

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).
  • Published: 2017
  • Publisher: Leibniz Universität Hannover (LUH), Institut für Meteorologie und Klimatologie
  • Language: Silent film
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