プッシュプル完全局排方式に関する基礎研究（第3報流れ特性に及ぼすノズル・フード間距離の影響）

概要

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In the first report, we investigated the characteristics of mean velocity such as the changes in mean velocity component profiles, and half-widths (b1/2) of the mean velocity profile in the downstream direction. In our second report, we investigated turbulence characteristics such as turbulence intensity, Reynolds shear stress, and intermittency of turbulence. We carried out all experiments thus far under the condition that the distance between the nozzle and hood is constant. In this third report, we have experimentally investigated the above flow characteristics of Push-Pull flow under the condition that the distance between nozzle and hood (L) is variable. Then we operated the Push-Pull local ventilation systems at each leakage-limit flow ratio with three different distances between the nozzle and hood, respectively. As the result, the existence of a region where the flow of air accelerates in the downstream direction became clear near the hood as the distance L became longer. In this region, an increase rate of half-widths in the downstream direction near the hood became smaller. At the same time, the flow of air and the velocity of entrainment near the hood rapidly increased. Also, turbulence intensity in the axial direction becomes smaller in the downstream direction as the distance L becomes greater. The value approaches that of the intensity in the lateral direction. Reynolds shear stress decreases in the downstream direction.