抄録
In this study, large-eddy simulation (LES) is performed to create the LES database to investigate the validity of the gradient diffusion approximation of the Reynolds stress within and above the urban canyon. It is confirmed that the LES database is more reliable than standard k-ε model (k-ε) within and above the urban canyon by comparing with the result of the wind tunnel experiment. k-ε fails to reproduce the spatial distribution of mean wind velocity within the urban canyon. The budget of Reynolds stress (<u1'u3'>) transport equation is analyzed using the LES database to investigate the validity of the gradient diffusion approximation. Within the urban canyon, the diffusion term of <u1'u3'> transport equation increases. The gradient diffusion approximation of <u1'u3'> is not valid within the urban canyon because the nonlocal effect of the diffusion term increases.
