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TURBULENT BOUNDARY LAYER FLOW SIMULATIONS OVER URBAN-LIKE ROUGHNESS USING LES

Kojiro Nozawa
Institute of Technology Shimizu Corporation 4-17, Etchujima 3-Chome, Koto-ku, Tokyo 135-8530, Japan

Tetsuro Tamura
Department of Environmental Science and Technology, Tokyo Institute of Technology 4259 Nagatsuta, Yokohama 226-8502, Japan

Аннотация

In this study, large eddy simulations of boundary layer flows over large-scale roughness have been performed targeting the experiments conducted by Cheng and Castro (2002). In order to duplicate the experimental conditions, the quasiperiodic boundary method for rough-wall boundary flows was applied to the inlet boundary conditions. The spatial variation of vertical profiles of mean and fluctuation velocities are studied in detail and compared to the experimental data. We focus on the influence on the spatial variations of turbulence structure deduced by large-scale roughness. The characteristics of the turbulent boundary layer flows over urban-like roughness (with a roughness area density of 25% and a boundary layer height ratio δ/h around 7) were different from the common homogenous roughness with δ/h larger than 50. The variable height of the roughness elements increased the zero-plane displacement height and the roughness length compared to those of uniform height roughness.