正方形断面から円形断面に変化する遷移ダクト内の乱流構造解析

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In this paper we describe numerical analysis to investigate the three-dimensional turbulent structure and fluid flow behavior in a square-to-circular transition duct. The hydraulic diameter, 40mm, was the same in the square inlet and round exit sections, resulting in a cross-sectional area reduction of 21.5 percent. The transition takes place over two hydraulic diameters. In the calculation, an algcbraic Reynolds stress model combined with a boundary-fitted coordinate system is applied to a square-to-circular transition duct in order to solve anisotropic turbulent flow precisely. The calculated results are compared with the experimental results available to examine the validity of the present method. As a result of calculation, it is found that the present method predicts streamwise and horizontal mean velocities well but the calculated distributions of the normal stresses show a discrepancy compared with the experiment. Although the flow was fully developed at the inlet to the transition duct, as stated in the experimental report, the experimental results of normal stresses differ greatly from those of flow, while calculated results are similar to those for fully developed flow. In this transition duct, two kinds of the secondary flow exist, i.e., one is the secondary flow of the second kind in the square duct and the other is that of the first kind in the transition duct induced by the pressure gradient. Moreover, the secondary flow of the transition duct disappears when the flow enters the duct with a circular cross section. The present method can predict these features quantitatively.
一般社団法人日本機械学会の論文
1997-04-25

正方形断面から円形断面に変化する遷移ダクト内の乱流構造解析

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