低レイノルズ数におけるk形粗面境界層の粗さ要素近傍の構造 : 溝部界面における干渉と溝内部流のパターン(流体工学, 流体機械)

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Measurements of the mean and the turbulent velocities have been performed in the vicinity of a roughness element for the turbulent boundary layer developing over a k-type rough wall, which consists of two-dimensional square ribs arrayed with pitch ratio of 4. The Reynolds-numbers based on momentum thickness θ and roughness height k are about 500 and 50 respectively, and relative roughness height k/δ6=0.156. LDV (Laser Doppler Velocitimetry) that it is capable to measure reverse flow was used in order to clarify the momentum-exchange process in the open-face (y_T=0 mm) between roughness elements and the flow-pattern in a groove. The variation of the mean and the turbulent quantities profiles at Y_T=0 mm depends on the development of a free-shear flow formed with disappearance of the roughness element and the formation of eddies in the groove. Pressure drag coefficient acting on the roughness element in the local skin friction coefficient is 92% in the present k-type rough wall. The momentum exchange for the mean flow and turbulence contribute 6% and 59% respectively to the local skin friction coefficient. The existence of a large-scale eddy and two small corner-eddies is confirmed from the flow pattern in the groove.
2002-09-25