Urban neighbourhood LES
- TOC "gallery/toc" is empty!
The following sequences show different flow aspects and phenomena of the neutrally stratified urban boundary layer. Simulations differ in domain size and grid resolution.
| LES of a city quarter of Hanover (Allianz tower, 2006)
|
|---|
|
|
Project: none
Responsible: Siegfried Raasch?
Description:
Turbulent flow around a city quarter of Hannover. The mean flow is from west (right) with a speed of 1 m/s (neutral stratification is assumed). Clouds of particles are periodically released in front of the large building (Allianz tower) and in the courtyard of another complex of buildings. The particle color reflects the height above ground (red: high, blue: low). Topography data are from laser altimeter measurements (kindly provided by the Institut für Kartographie und Geoinformatik, Leibniz Universität Hannover). The resolution of the laser data allows to resolve cars on the street west of the Allianz building, staying there because of a red traffic light. The sequence shows that the turbulent flow within street canyons is highly variable so that flow directions may change completely within short times.
| Model Setup
|
|---|
| Total domain size (x|y|z): | 256m x 256m x 200m
| | Grid spacing (x|y|z): | 1m x 1m x 1m
| | Number of grid points (x|y|z): | 256 x 256 x 200
| | Simulated time: | 1h
| | CPU-time: | 1800s
| | Number of CPUs: | 32
| | Machine/ processor type: | IBM-Regatta / Power4
| | Visualization software: | DSVR
|
| Download
|
|---|
| Video Format | File size
| | Flash (.flv) | 8.3mb | Download
| | MPEG (.avi) | 8.3mb | Download
|
|
| Turbulent flow around high-rise office buildings in downtown Tokyo (2008)
|
|---|
|
|
Project: High resolution LES of turbulent flow in the vicinity of buildings including thermal effects
Responsible: Marcus Letzel
Original online publication:
- Letzel, M. O., G. Gaus, S. Raasch, N. Jensen and M. Kanda, 2008: Turbulent flow around high-rise office buildings in downtown Tokyo. Dynamic Visualization in Science, No. 13100, originally published under the URL http://www.dyvis.org/DyVis?Sig=13100.
Associated journal publication with cross-reference:
Description:
The parallelized large-eddy simulation (LES) model PALM simulates a neutral turbulent urban boundary layer in Shinjuku, downtown Tokyo, Japan using GIS data provided by CADCENTER, Tokyo.
The simulation lasts 3 h with a domain size of 900 m x 900 m x 492.5 m, periodic boundary conditions and 5 m uniform grid length. The model is driven by a 1 m/s westerly wind applied at the top of the domain (Couette flow) and initialized with a vertical profile obtained from a 1D model prerun.
PALM’s Lagrangian particle model is used to track passive tracers with 1 h lifetime that are released every 5 min from four vertical line sources (colour ~ current height, tail length ~ velocity).
Particles in front of the metropolitan twin towers travel far upstream close to the ground during the first 15 min because turbulence has not yet fully developed. During most of the simulation the flow is channeled by tall buildings acting as street canyons. Zoom views show particle paths under the influence of eddies and helical vortex structures shed off the large buildings. Intermittent low-level upstream flow is evident in the most southerly street canyon particularly during t = 92…121 min when several blue (low-level) particles travel westwards (upstream). These features highlight the ability of LES models to capture turbulent fluctuations.
The Doc-Show Virtual Reality (DSVR) framework used for visualization consists of three subsystems: a parallelized library coupling to PALM, where geometry is created via FORTRAN or C function calls, a streaming server receiving the simulation results, storing the geometry and serving viewing clients and a browser plugin permitting real-time interactive presentation in various modes, including variation of lighting and thickness of particle tails. The level of detail of the geometry can be seen in wireframe mode during t = 62…80 min, when all rendered surfaces are shown as triangular primitives. The resulting transparency effect permits to look through surfaces.
| Model Setup
|
|---|
| Total domain size (x|y|z): | 900.0m x 900.0m x 492.5m
| | Grid spacing (x|y|z): | 5m x 5m x 5m
| | Number of grid points (x|y|z): | 180 x 180 x 100
| | Simulated time: | 10800s
| | CPU-time: | 1.1h
| | Number of CPUs: | 30
| | Machine/ processor type: | IBM-Regatta / Power4
| | Visualization software: | DSVR
|
| Download
|
|---|
| Video Format | File size
| | WMV (.wmv) | 95mb | Download (original movie from DyVis)
| | Flash (.flv) | 37mb | Download (original bitrate)
| | Flash (.flv) | 22mb | Download (reduced bitrate)
|
|
| Turbulent flow in a densely built-up area in Kowloon, downtown Hong Kong (2008)
|
|---|
|
|
Projects:
Responsible: Marcus Letzel
Original online publication:
- Letzel, M. O., G. Gaus, 2008: Turbulent flow in a densely built-up area in Kowloon, downtown Hong Kong. Dynamic Visualization in Science, No. 13118, originally published under the URL http://www.dyvis.org/DyVis?Sig=13118.
Associated journal publication with cross-reference:
- Letzel, M.O., C. Helmke, E. Ng, X. An, A. Lai and S. Raasch, 2012: LES case study on pedestrian level ventilation in two neighbourhoods in Hong Kong. Meteorol. Z., accepted.
Description:
To follow.
| Model Setup
|
|---|
| Total domain size (x|y|z): | 768.0m x 512.0m x 400.0m
| | Grid spacing (x|y|z): | 1m x 1m x 0.8m
| | Number of grid points (x|y|z): | 768 x 512 x 325
| | Simulated time: | 10800s
| | CPU-time: | 77h
| | Number of CPUs: | 128
| | Machine/ processor type: | IBM-Regatta / Power4
| | Visualization software: | DSVR
|
| Download
|
|---|
| Video Format | File size
| | WMV (.wmv) | 30mb | Download (original movie from DyVis)
| | Flash (.flv) | 35mb | Download (original bitrate)
| | Flash (.flv) | 14mb | Download (reduced bitrate)
|
|
