建築物周辺気流を対象とする風洞実験における閉塞効果

Abstract

This paper reports the wind tunnel experiments conducted to study the blockage effects on air flow around buildings. It sees that the wind tunnel air flow will be geometrically similar to each building model and finally aims at the determination of a more proper size of the test objects. Variously scaled cubic building models were placed in the turbulent boundary layer whose mean wind velocity was distributed similarly to height of each model, revealing the exact effects due to the blockage. Measurements were performed in the three dimensional way for the air flow around each model, explicating the distribution of wind velocity not only near the surface region but also in total one. The result is as follows : Higher the blockage ratio gets, wider the corner flow region becomes. This tendency is easy to be appeared near to the surface level. The maximum value of mean wind velocity in the corner flow region is directly proportional to the blockage ratio. In the case that the blockage ratios less than 3.57 %, no significant changes of distribution of mean velocity can be seen around the models except for the corner flow region. The result of these experiments as is stated above contributes to conclude that the effective model area normal to the wind direction should be less than 1 % of the wind tunnel cross-sectional area.