Flow simulations for simplified urban configurations with microscale distributions of surface thermal forcing

•Realistic distributions of heat fluxes at urban surfaces are used in CFD model.•Different solar positions and intensities of buoyancy forces are studied.•An adimensional parameter (H/Lurb) is suitable to classify the cases.•H/Lurb determines the importance of buoyancy forces relative to mechanical forces.•Sectional drag coefficient varies substantially for cases with high H/Lurb.

Effects of solar position and of the ratio of buoyant to inertial forces on flow properties (wind speed and temperature) within an array of urban-like obstacles are investigated. An aligned array of cubes with a plan area density of 0.25 is studied. First, distributions of sensible heat fluxes on built surfaces for different solar positions are determined by the Temperatures of Urban Facets in 3-D (TUF3D) model, a microscale three-dimensional urban energy balance model. These fluxes provide boundary conditions to a Reynolds-Averaged Navier–Stokes (RANS) model, which simulates flow and temperature over the array. Results are evaluated against experimental measurements. Furthermore, microscale variation of flow and temperature as a function of the ratio of buoyant to inertial forces is analyzed. Finally, spatially-averaged flow properties are determined as a function of this ratio, and inform neighbourhood-scale parameterizations for mesoscale modeling of urban flows. Differences between configurations are larger at the microscale than the neighbourhood (spatially-averaged) scale. Spatially-averaged flow properties are impacted primarily for scenarios with high buoyancy-to-inertial force ratios. In addition, an analysis of stationary vs. unsteady flow simulations is made.