Robustness of the Mean Flow Similarity in an Urban Roughness Sublayer to Different Inflow Properties

This study uses a numerical simulation to examine the local mean flow similarity within an urban roughness sublayer (RSL). The simulations are conducted using a realistic building geometry for the central area of Tokyo under three different inflow conditions. The inflow properties are controlled by changing the surface geometries in the upwind direction, which results in various ratios of boundary-layer height to roughness height in the target region. The local mean wind velocities within the RSL, which vary significantly in space, are proportional to each other in all simulations, regardless of the inflow conditions. The velocity within the RSL is represented by the friction velocity, which is estimated from the Reynolds stress profile in the inertial sublayer. The behaviour of the wake turbulence behind isolated high-rise buildings differs considerably among the inflow conditions. Velocity persists for long distances downstream in cases with a low boundary- layer height relative to an isolated building, whereas it diffuses rapidly in cases with a higher boundary-layer height. This effect can propagate into the RSL and modify the mean flow similarity within the sublayer.