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 us ing the computational fluid dynamics technique. The numerical scheme is fir st applied to a backward-facing step flow over a wide range of Reynolds num bers. Good agreement with experimental data from literature is found. It is then applied to study the Row around two rectangular buildings with variou s building heights, gap distances, and approaching wind velocities. Simulat ions show that the wind profile upstream of buildings is similar under diff erent inflow wind velocities for a fixed building height. The maximum wind velocity in the street canyon largely depends on the configuration of the b uildings. It increases dramatically when the gap-to-height ratio (G/H) of t he 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 how 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 stac k vertically in the street canyon, are found for H/G greater than or equal to 3. For those simulations with nonidentical buildings, natural ventilatio n tends to be better in the case of the higher building located upstream.