Study on Airflow around Building Roof for Design of Natural Ventilationby Chimney-Part2 Wind Velocity Distribution above Building Roof-

The purpose of this study is to clarify thecharacteristics of airflow around building roofand to provide the guidelines for design ofnatural ventilation by chimney. Previous past ofthis paper showed the distribution of windpressure coefficient on flat rooftop of buildingsobtained from the wind tunnel test to find theproper position of a chimney on building roof.This past of the paper shows the wind velocitydistribution above building roof to find theproper height of a chimney and to analyze thecharacteristics of separated flow above buildingroof.Wind tunnel test was carried out with twodifferent models. The height was 200mm andthe dimension of the rooftop was1 OOmmx 1 OOmm and 100mmx200mm.Measurement points are located at 5 to 50mmabove fiom the surface of building roof.Boundary layer was made in the wind tunnel.Wind direction was changed as 0, 22.5", 45"and 90". Wind velocities above the building roofwere measured with hot-wire anemometer.Based on the experimental data, the betterposition and height of chimneys on buildingroof are presumed depending on the aspect ratioof the building and wind direction.As a result, some tendencies were obtained.From the viewpoint of geometry of each model,separation of airflow mainly depends on thewindward wall area. In contrast, the depth of themodel has less effect. In addition, in case ofwindward side of rooftop, chimney height canbe lowered.