Evaluation of k-ε Reynolds stress modeling in an idealized urban canyon using LES

Abstract

In this study, a large-eddy simulation (LES) was conducted to investigate the validity of the modeling of Reynolds stress in standard k-ε model (k-ε model) for urban canyon flow. It was confirmed that the LES was more reliable than the k-ε model for urban canyon flow, through a comparison of experimental results. The k-ε model failed to reproduce the spatial distribution of the mean velocity within the urban canyon. It underestimated the absolute value of Reynolds stress <u1'u3’> and eddy viscosity coefficient νt, when compared to the LES. On the leeward side of the urban canyon, νt obtained by the LES was negative and the counter gradient diffusion was seen to occur. The budget of <u1'u3’> transport equation was analyzed using the results of the LES. At the top of the urban canyon and within it, the convection and diffusion terms showed an increase when compared to the production and pressure strain correlation terms. The gradient diffusion approximation of <u1'u3’> was not valid because the local equilibrium of <u1'u3’> transport equation was not correct. It was found necessary to incorporate the effect of the convection and diffusion terms in the modeling of <u1'u3’> for urban canyon flow.