Details
| Original language | English |
|---|---|
| Pages (from-to) | 8770-8784 |
| Number of pages | 15 |
| Journal | Atmospheric environment |
| Volume | 42 |
| Issue number | 38 |
| Early online date | 15 Aug 2008 |
| Publication status | Published - Dec 2008 |
Abstract
Urban turbulence characteristics are investigated at street canyon and neighbourhood scale. Three high resolution urban large-eddy simulation (LES) studies are performed using the urban version of the parallelized LES model PALM. Validation shows that the urban PALM version is in line with experimental and previous LES results, i.e. superior to the faster/cheaper conventional Reynolds-averaged (RANS) models. Two studies focus on quasi-2D urban street canyons driven by perpendicular flow. First is a parametric study of turbulence characteristics and flow dynamics within the canyon. The main results are: (1) Integral vertical turbulence profiles in deep canyons scale with canyon width. This is relevant for urban canopy parameterizations in larger-scale meteorological models. (2) A new concept of a "cavity shear layer" complements classical free shear layer concepts. (3) For the first time in urban LES Kelvin-Helmholtz instabilities are identified at the top of the urban street canyon. This is relevant for modelling urban dispersion, because the street canyon circulation is more intermittent than suggested by previous RANS results. Second, an Eulerian dispersion case study shows that differences in canyon flow dynamics are reflected in canyon dispersion characteristics compared to a previous RANS study. Third is a neighbourhood scale urban LES feasibility study: a passive tracer Lagrangian dispersion animation of Shinjuku, downtown Tokyo reveals turbulent flow features, upstream flow and intermittency. The main implications are always to use 3D models for turbulence simulations even in quasi-2D geometries, and not to underestimate the intermittency of turbulent flow. Standard deviations of velocity components within the canyon should not be treated as constant for perpendicular ambient wind but may be parameterized conveniently based on a vertical scaling with canyon width in deep canyons.
Keywords
- Atmospheric dispersion, Complex topography, Street canyon, Turbulent flow visualization, Urban large-eddy simulation
ASJC Scopus subject areas
- Environmental Science(all)
- Earth and Planetary Sciences(all)
- Atmospheric Science
Cite this
- Standard
- Harvard
- Apa
- Vancouver
- BibTeX
- RIS
In: Atmospheric environment, Vol. 42, No. 38, 12.2008, p. 8770-8784.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - High resolution urban large-eddy simulation studies from street canyon to neighbourhood scale
AU - Letzel, Marcus Oliver
AU - Krane, Martina
AU - Raasch, Siegfried
N1 - Funding Information: Financial support by the German Research Foundation (DFG) under grants RA 617/6-1 and RA 617/15-1, by the German National Academic Foundation and by the German National Academic Exchange Service (DAAD) is gratefully acknowledged. Furthermore, the authors would like to thank M. Kanda, J.-F. Sini, S. Olbrich, N. Jensen, G. Gaus, and K. Ketelsen for their scientific and code optimization support. Two anonymous reviewers provided constructive suggestions. GIS data of Tokyo Shinjuku were provided by CADCENTER Tokyo through M. Kanda; the animation was produced by IWF Knowledge and Media. The simulations were performed on the German supercomputing centers HLRN and DKRZ.
PY - 2008/12
Y1 - 2008/12
N2 - Urban turbulence characteristics are investigated at street canyon and neighbourhood scale. Three high resolution urban large-eddy simulation (LES) studies are performed using the urban version of the parallelized LES model PALM. Validation shows that the urban PALM version is in line with experimental and previous LES results, i.e. superior to the faster/cheaper conventional Reynolds-averaged (RANS) models. Two studies focus on quasi-2D urban street canyons driven by perpendicular flow. First is a parametric study of turbulence characteristics and flow dynamics within the canyon. The main results are: (1) Integral vertical turbulence profiles in deep canyons scale with canyon width. This is relevant for urban canopy parameterizations in larger-scale meteorological models. (2) A new concept of a "cavity shear layer" complements classical free shear layer concepts. (3) For the first time in urban LES Kelvin-Helmholtz instabilities are identified at the top of the urban street canyon. This is relevant for modelling urban dispersion, because the street canyon circulation is more intermittent than suggested by previous RANS results. Second, an Eulerian dispersion case study shows that differences in canyon flow dynamics are reflected in canyon dispersion characteristics compared to a previous RANS study. Third is a neighbourhood scale urban LES feasibility study: a passive tracer Lagrangian dispersion animation of Shinjuku, downtown Tokyo reveals turbulent flow features, upstream flow and intermittency. The main implications are always to use 3D models for turbulence simulations even in quasi-2D geometries, and not to underestimate the intermittency of turbulent flow. Standard deviations of velocity components within the canyon should not be treated as constant for perpendicular ambient wind but may be parameterized conveniently based on a vertical scaling with canyon width in deep canyons.
AB - Urban turbulence characteristics are investigated at street canyon and neighbourhood scale. Three high resolution urban large-eddy simulation (LES) studies are performed using the urban version of the parallelized LES model PALM. Validation shows that the urban PALM version is in line with experimental and previous LES results, i.e. superior to the faster/cheaper conventional Reynolds-averaged (RANS) models. Two studies focus on quasi-2D urban street canyons driven by perpendicular flow. First is a parametric study of turbulence characteristics and flow dynamics within the canyon. The main results are: (1) Integral vertical turbulence profiles in deep canyons scale with canyon width. This is relevant for urban canopy parameterizations in larger-scale meteorological models. (2) A new concept of a "cavity shear layer" complements classical free shear layer concepts. (3) For the first time in urban LES Kelvin-Helmholtz instabilities are identified at the top of the urban street canyon. This is relevant for modelling urban dispersion, because the street canyon circulation is more intermittent than suggested by previous RANS results. Second, an Eulerian dispersion case study shows that differences in canyon flow dynamics are reflected in canyon dispersion characteristics compared to a previous RANS study. Third is a neighbourhood scale urban LES feasibility study: a passive tracer Lagrangian dispersion animation of Shinjuku, downtown Tokyo reveals turbulent flow features, upstream flow and intermittency. The main implications are always to use 3D models for turbulence simulations even in quasi-2D geometries, and not to underestimate the intermittency of turbulent flow. Standard deviations of velocity components within the canyon should not be treated as constant for perpendicular ambient wind but may be parameterized conveniently based on a vertical scaling with canyon width in deep canyons.
KW - Atmospheric dispersion
KW - Complex topography
KW - Street canyon
KW - Turbulent flow visualization
KW - Urban large-eddy simulation
UR - http://www.scopus.com/inward/record.url?scp=55549100908&partnerID=8YFLogxK
U2 - 10.1016/j.atmosenv.2008.08.001
DO - 10.1016/j.atmosenv.2008.08.001
M3 - Article
AN - SCOPUS:55549100908
VL - 42
SP - 8770
EP - 8784
JO - Atmospheric environment
JF - Atmospheric environment
SN - 1352-2310
IS - 38
ER -