Numerical Study on Flow over Buildings in Street Canyon

A 2D numerical investigation of the relationships between building height, gap distance, and wind velocity for flow in a street canyon is conducted using the computational fluid dynamics technique. The numerical scheme is first applied to a backward-facing step flow over a wide range of Reynolds numbers. Good agreement with experimental data from literature is found. It is then applied to study the flow around two rectangular buildings with various building heights, gap distances, and approaching wind velocities. Simulations show that the wind profile upstream of buildings is similar under different inflow wind velocities for a fixed building height. The maximum wind velocity in the street canyon largely depends on the configuration of the buildings. It increases dramatically when the gap-to-height ratio (G/H) of the buildings is increased from 0.75 to 1.0 but increases only mildly for G/H rising from 1.0 to 1.5. No significant increase in velocity can be found for a further increase in G/H. The flow pattern in the street canyon becomes more complex with an increasing height-to-gap ratio (H/G), particularly at low inflow velocity. Two or more stable recirculation vortices, which stack vertically in the street canyon, are found for H/G ≥ 3. For those simulations with nonidentical buildings, natural ventilation tends to be better in the case of the higher building located upstream.