Repository: Freie Universität Berlin, Math Department

A New Aerodynamic Parameterization for Real Urban Surfaces

Kanda, M. and Inagaki, A. and Miyamoto, T. and Gryschka, M. and Raasch, S. (2013) A New Aerodynamic Parameterization for Real Urban Surfaces. Boundary-Layer Meteorology, 148 . pp. 357-377.

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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 abovewas empirically proposed. The new parametrizations work well for both real urban morphologies and simplified model geometries.

Item Type:Article
Subjects:Mathematical and Computer Sciences > Mathematics > Applied Mathematics
ID Code:1384
Deposited By: Ulrike Eickers
Deposited On:21 Feb 2014 12:09
Last Modified:21 Feb 2014 12:09

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