| | 12 | |
| | 13 | '''Project:''' [[imuk/projects|High resolution large-eddy simulations of the urban canopy flow in Macau]] \\ |
| | 14 | \\ |
| | 15 | '''Responsible:''' [[imuk/members/keck|Marius Keck]], [[imuk/members/knoop|Helge Knoop]]\\ |
| | 16 | \\ |
| | 17 | '''Description:''' 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 [[http://palm.muk.uni-hannover.de/|PALM]], 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 [[http://www.vapor.ucar.edu/|VAPOR]]. 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/|HLRN]]). |
| | 18 | |
| | 19 | 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 . |
| | 20 | |
| | 21 | 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.\\ |
| | 22 | |
| 20 | | \\ |
| 21 | | }}} |
| 22 | | {{{#!td style="vertical-align:top; border: 0px solid"" |
| 23 | | '''Project:''' [[imuk/projects|High resolution large-eddy simulations of the urban canopy flow in Macau]] \\ |
| 24 | | \\ |
| 25 | | '''Responsible:''' [[imuk/members/keck|Marius Keck]], [[imuk/members/knoop|Helge Knoop]], [[imuk/members/raasch|Siegfried Raasch]]\\ |
| 26 | | \\ |
| 27 | | '''Description:''' 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 [[http://palm.muk.uni-hannover.de/|PALM]], 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 [[http://www.vapor.ucar.edu/|VAPOR]]. 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/|HLRN]]). |
| | 46 | \\ |
| | 47 | '''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). |
| | 48 | |
| | 49 | 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. |
| | 50 | |
| | 51 | 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.\\ |
| 56 | | '''Description:''' \\ |
| 57 | | 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.\\ |
| 58 | | 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.\\ |
| 59 | | 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).\\ |
| 60 | | 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.\\ |
| 61 | | 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.\\ |
