中性与稳定层结条件下建筑物周围流场与污染物扩散的风洞模拟研究

Wind Tunnel Simulation Study of Flow and Diffusion Around a Building Under Neutral and Stable Thermal Stratification

通过风洞实验研究了中性(Ri_b=0)和稳定层结(Ri_b=0.057)条件下建筑物周围流场与污染物扩散规律,采用冷线和热线相结合的方式测量了建筑物周围的平均流和湍流结构,采用示踪实验方法研究了中性和稳定层结条件下污染物浓度分布特征。分析表明,当大气处于稳定层结条件下时,纵向速度和湍流强度略小于中性层结。不同温度层结对建筑物近场污染物扩散的影响不同,稳定层结抑制了垂直方向污染物的扩散,使得污染物浓度增大。最大归一化浓度出现在靠近建筑物的位置(x/H=1/3),出现的高度在z=1.2H处,稳定层结下最大归一化浓度K=11,中性层结下最大归一化浓度K=7.随着下风向距离的增加,浓度峰值出现的高度下降,且相较于中性层结,稳定层结条件下峰值出现的高度较低。

The flow and diffusion around a building under neutral(Ri b=0)and stable stratification(Ri b=0.057)conditions were investigated by wind tunnel experiment.The mean flow and turbulent structure around the building were measured by a combination of hot wire and cold wire.The characteristics of pollutant concentration distribution under neutral and stable stratification conditions were investigated by using tracer experiments.The results indicate that when atmospheric stratification is stable,the longitudinal velocity and turbulence intensity are lower than under neutral conditions.Different thermal stratification has different effect on the diffusion around a building.Stable thermal stratification inhibits the diffusion of pollutants in the vertical direction,which causes an increase in concentrations.The maximum normalized concentration appears near the building(x/H=1/3,z/H=1.2).The maximum normalized concentration is 11 for the stable condition and 7 for the neutral condition.As the downwind distance increases,the height of the concentration peak decreases.Compared with neutral thermal stratification,stable thermal stratification gives a lower concentration peak value.