報告書番号

N07031

タイトル（和文）

大規模主流擾乱が重畳する平板境界層の乱流特性

タイトル（英文）

Turbulence characteristics of boundary layer flow along a flat plate beneath large-scale inflow turbulence

概要 （図表や脚注は「報告書全文」に掲載しております）

大規模な主流擾乱が重畳する平板境界層の乱流特性を実験的に検討した．アクティブ乱流格子法を使って，主流擾乱の乱流強度とスケールを変化させた．2成分の瞬時風速をx型熱線により計測し，高次モーメントを含む乱流統計量と取得した．そして，大規模な主流擾乱が，平板近傍を含む境界層の乱流構造に直接的に影響し，大規模な主流擾乱を付加した場合，一般的な境界層と異なり，外層から壁近くに入り込む高速流体塊の運動が，乱流生成に深く関与することを明らかにした．一方，平均風速や乱流運動量フラックスの境界層内分布は主流条件に依存しない．これとは異なり，乱流強度の境界層内分布は，主流擾乱の付加とともに変化する．

概要 （英文）

The turbulence characteristics of boundary layer beneath the large-scale inflow turbulence have been experimentally investigated. Using an active turbulence grid, the turbulence intensity and length-scale involved in the inflow were varied. The 2-component instantaneous velocities were measured with an X-type hot wire, and turbulence statistics, including higher order moments, were accumulated. Through the measurements, it was found that the large-scale velocity fluctuation of inflow turbulence directly affects on the turbulence structure in the boundary layer even for the near-wall region, and the turbulence generation in the boundary layer with large-scale inflow turbulence is closely related to the 'Q4' motions (sweep) with large-scale velocity fluctuation, while that of normal wall turbulence is mainly caused by 'Q2' motions (ejection). Nevertheless, the profiles of mean velocity and turbulence momentum flux against distance from the surface are independent of the conditions of inflow turbulence. Contrary to this, the profiles of turbulence intensity and skewness and flatness factors of fluctuating velocities significantly change with the inflow turbulence.

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