短い入口助走管路を有する曲がり管路内の乱流構造解析 : 流入境界層の曲がり管路内流動への影響

概要

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A numerical analysis has been performed on developing turbulent flow in a square-sectioned 180 deg bend. The ratio of bend mean radius of curvature to hydraulic diameter is 3.375 and a straight duct 6 hydraulic diameters long is attached to the inlet plane of the bend. In calculation, an algebraic stress model was adopted in order to predict Reynolds stresses precisely, and a boundary-fitted coordinate system was introduced as the method of coordinate transformation. Calculated results were compared with the experimental data available. Moreover, the influence of boundary layer thickness at the bend entry is examined using the calculated results. As a result of this study, we conclude that the present method can predict well the mean flow velocity as well as its a minimum and the measured spike velocity in streamwise velocity fluctuations near the symmetry at 90 deg. Furthermore the calculated results confirm that thinner entry boundary layers in the turbulent flow give rise to lower cross-stream velocity. As a characteristic feature, it is pointed out that the secondary flow breaks down into several eddies in the place of the classical single vortex structure when the boundary layers are thin. Therefore, distorted contour lines of streamwise flow appear at angles greater than 90 deg where the secondary flow begins to break down.
社団法人日本機械学会の論文
1996-01-25