Wind-tunnel measurements for thermal effects on the air flow and pollutant dispersion through different scale urban areas

A multiscale physical model was built to study the basic phenomena of air flow, heat and mass transfer passing through different scale urban areas. Wind-tunnel measurements were conducted in TJ-1 and TJ-4 wind tunnels with ground heating to model solar radiation and SF6 released from upwind building rooftop. Particle image velocimetry (PIV), T-type thermocouples and SF6 quantitative detector were used to measure flow fields, temperature and pollutant distributions. Thermal effects on flow structures were modeled for Richardson numbers (Ri) from 0 to 4.77. Measurement results show that for the investigation of mixed convection in the street canyon by wind tunnel, if the value of Reynolds number is in the range of Re-independence determined by forced boundary layer flow, the only criterion for flow pattern and temperature distribution of the external flow is the Richardson number. By cross ventilation, the temperature and pollution distributions in the street canyon and those within the room are inherently related, in that the mixed temperature and pollution in the room only depend on the street Ri if the room wall is adiabatic for both heat and mass transfer. Detailed results for velocity, temperature and pollution are provided for eight cases with different Richardson numbers.