A wind-tunnel study of peak concentration in the near-wake region of a cubical model building

Abstract

A wind tunnel study of peak concentrations in the near-wake region of a cubical model was conducted. Tracer gas was emitted from the rooftop at the center of the model and was measured with a fast-response concentration detector. The results showed that there were two dispersion regimes in the building wake. One regime, labeled the “mixing regime”, was approximately below the middle of the buiding. The other regime, designated the “intermittency regime”, was approximately above the middle of the building. In the mixing regime, the peak of the concentration spectrum were observed in a low frequency region, while, in the intermittency regime, the peak appeared to shift to wards a higher frequency region. The gust factor (G_f) near the building wake has a considerable scatter range of G_f=3-20. On the other hand, the peak factor has a small scatter range of 4-7. The relationship between the peak factor (P_f) and averaging time (T_a) can be expressed by the equation P_f = 9.1 T_a^-0.46 in the range of T_a =1-200s, where T_a is the time in prototype time.