Numerical modelling of solar thermal effects on street canyon flow under calm or weak wind conditions

The present study simulates the flow and temperature fields in a street canyon caused by solar heating of road and building surfaces, in either calm and weak wind conditions. Six scenarios, formed by changing the sources of heat fluxes, the wind speed (0, 1 and 3 m s^-1) and direction (±), are examined, at 12:00 solar time during June 21 in the city of Patras. A 1000-W m^-2 heat flux is considered to come out from the road surface and/or 400-W m^-2 heat flux from the left building face. These values correspond to the most intense solar radiation conditions. A computational fluid dynamics (CFD) simulation is performed and the results show that the weak winds cause increased temperatures near the building faces compared to calm conditions, due to intense vortices that entrap air masses, while moderate winds contribute to an improvement of temperatures below those for calm conditions. The entrapment of air masses may also cause increase of pollutant concentrations deteriorating both outdoor and indoor air quality and thermal comfort conditions.