TY - JOUR

T1 - A New Aerodynamic Parametrization for Real Urban Surfaces

AU - Kanda, Manabu

AU - Inagaki, Atsushi

AU - Miyamoto, Takashi

AU - Gryschka, Micha

AU - Raasch, Siegfried

N1 - Funding Information: Acknowledgments This research was financially supported by Research Program on Climate Change Adaptation (RECCA), a Grant-in-Aid for Scientific Research (B): 21360233, and a Grant-in-Aid for Young Scientists (B): 23760454 from the Ministry of Education, Culture, Sports, Science and Technology, Japan. This research was also supported by the German Research Foundation under Grant RA 617/15-2.

PY - 2013/8

Y1 - 2013/8

N2 - This study conducted large-eddy simulations (LES) of fully developed turbulent flow within and above explicitly resolved buildings in Tokyo and Nagoya, Japan. The more than 100 LES results, each covering a 1,000 × 1,000 m2 area with 2-m resolution, provide a database of the horizontally-averaged turbulent statistics and surface drag corresponding to various urban morphologies. The vertical profiles of horizontally-averaged wind velocity mostly follow a logarithmic law even for districts with high-rise buildings, allowing estimates of aerodynamic parameters such as displacement height and roughness length using the von Karman constant= 0.4. As an alternative derivation of the aerodynamic parameters, a regression of roughness length and variable Karman constant was also attempted, using a displacement height physically determined as the central height of drag action. Although both the regression methods worked, the former gives larger (smaller) values of displacement height (roughness length) by 20-25 % than the latter. The LES database clearly illustrates the essential difference in bulk flow properties between real urban surfaces and simplified arrays. The vertical profiles of horizontally-averaged momentum flux were influenced by the maximum building height and the standard deviation of building height, as well as conventional geometric parameters such as the average building height, frontal area index, and plane area index. On the basis of these investigations, a new aerodynamic parametrization of roughness length and displacement height in terms of the five geometric parameters described above was empirically proposed. The new parametrizations work well for both real urban morphologies and simplified model geometries.

AB - This study conducted large-eddy simulations (LES) of fully developed turbulent flow within and above explicitly resolved buildings in Tokyo and Nagoya, Japan. The more than 100 LES results, each covering a 1,000 × 1,000 m2 area with 2-m resolution, provide a database of the horizontally-averaged turbulent statistics and surface drag corresponding to various urban morphologies. The vertical profiles of horizontally-averaged wind velocity mostly follow a logarithmic law even for districts with high-rise buildings, allowing estimates of aerodynamic parameters such as displacement height and roughness length using the von Karman constant= 0.4. As an alternative derivation of the aerodynamic parameters, a regression of roughness length and variable Karman constant was also attempted, using a displacement height physically determined as the central height of drag action. Although both the regression methods worked, the former gives larger (smaller) values of displacement height (roughness length) by 20-25 % than the latter. The LES database clearly illustrates the essential difference in bulk flow properties between real urban surfaces and simplified arrays. The vertical profiles of horizontally-averaged momentum flux were influenced by the maximum building height and the standard deviation of building height, as well as conventional geometric parameters such as the average building height, frontal area index, and plane area index. On the basis of these investigations, a new aerodynamic parametrization of roughness length and displacement height in terms of the five geometric parameters described above was empirically proposed. The new parametrizations work well for both real urban morphologies and simplified model geometries.

KW - Aerodynamic parametrization

KW - Displacement height

KW - Large-eddy simulation

KW - Real urban surfaces

KW - Three-dimensional building map

UR - http://www.scopus.com/inward/record.url?scp=84880508388&partnerID=8YFLogxK

U2 - 10.1007/s10546-013-9818-x

DO - 10.1007/s10546-013-9818-x

M3 - Article

AN - SCOPUS:84880508388

VL - 148

SP - 357

EP - 377

JO - Boundary-Layer Meteorology

JF - Boundary-Layer Meteorology

SN - 0006-8314

IS - 2

ER -