報告書番号

V09017

タイトル（和文）

日射による壁面加熱がストリートキャニオン内の流れおよび大気拡散に及ぼす影響に関する風洞実験

タイトル（英文）

Wind tunnel experiments for impacts of wall heating induced by solar radiation on the air flow and atmospheric dispersion within a street canyon

概要 （図表や脚注は「報告書全文」に掲載しております）

日射による建物壁面の加熱がストリートキャニオン内の流れや大気拡散に及ぼす影響を解明するための風洞実験を実施した。キャニオン風上側建物の風下面（leeward面）加熱時には，気流温度の鉛直分布は建物高さの壁面近くで急勾配を示し，キャニオンから上空に向かう大規模な上昇流が形成される。そのため，加熱壁面近傍の濃度は非加熱時より低い。本実験で得られたleeward面加熱時の流れ場は，これまでの2次元ストリートキャニオンを対象に行われた数値シミュレーション結果と大幅に異なっており，キャニオン側方から流入する流れがキャニオン内の渦形成に大きな影響を与えていることが明らかとなった。一方，風下側建物の風上面（windward面）加熱時には，加熱面近くにおいて熱浮力にともなう上昇流に誘起された反時計回りの渦が形成される。また，熱浮力による上昇流が上空からキャニオン内に下降する流れを阻害するため，キャニオン下層の濃度が大幅に上昇することが明らかとなった。

概要 （英文）

A series of wind tunnel experiments were conducted to determine thermal effects on the air flow and pollution dispersion within a street canyon. The experiments were performed in a thermally stratified wind tunnel at the Central Research Institute of Electric Power Industry (CRIEPI). The model buildings were made from phenolic plastic and aluminum board, the surfaces of which were heated from inside using a silicon rubber heater. The approach flow was perpendicular to the axis of the canyon, and wind velocities were measured using PIV. To examine the effects of wall heating on the canyon flow, three different heating conditions (neutral, leeward-wall-heated, and windward-wall-heated) and three free stream wind velocities were considered. In the leeward-wall-heated case, a large-scale updraft due to the buoyancy occurred frequently, and the air flow above the canyon was prevented from entering the canyon by the strong updraft; thus, a small clockwise vortex was formed only near the windward wall. As the Richardson number (Ri) decreased, the flow field tended to be similar to that observed in the neutral case. In the windward-wall-heated case, a clockwise vortex and a secondary counterclockwise vortex similar to those predicted using numerical models were observed. This secondary counterclockwise vortex tended not to appear as Ri decreased, and a large primary vortex was observed at the smallest value of Ri considered. Both air temperatures and tracer gas concentrations were also measured within the model street canyon and the effects of wall heating were investigated.

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