k形粗面境界層の粗さ要素近傍における乱流輸送機構(流体工学,流体機械)

概要

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Turbulent transport mechanism has been investigated in the vicinity of a roughness element for the boundary layer developing over a k-type rough wall consisting of two-dimensional square ribs. Measurements associated with the conditional averages for 4-quardrant analysis and the higher moments were made on the momentum thickness Reynolds number R_θ=⃥5800. The roughness Reynolds number k^+ is 120, which is fully rough regime. A new roughness density parameter λ_s is defined with considering turbulent transport over grooves between roughness elements, and it can be divided into two-types of the rough wall flows. For the fractional contribution to Reynolds shear stress -<uv>^^^- of the 4-quardrant analysis, the sweep event takes larger portion compared with the ejection event in the range of λ_s>0.6, which includes the present rough wall. On the other hand, the rough wall flows of λ_s<0.6 have the slightly large portion of the ejection event. The third moments associated with vertical turbulent flux indicate downward transport for λ_s≥0.7 and upward transport for λ_s<0.7. From these results and flow visualization of x-z plane near present k-type rough wall, it is explained in term of the existence of the vortex structure that forms necklace vortex type for λ_s>0.6〜0.7.
2003-10-25