Study on Miter-Bend Flow : Part 7-Numerical Study on Flow Mechanism in Turbulent Flow

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  • SUU Tetsuo
    Department of Mechanical Engineering, Faculty of Engineering, Utsunomiya University
  • FUJII Kiyomi
    Department of Mechanical Engineering, Faculty of Engineering, Utsunomiya University

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Other Title
  • 屈折管内の流れに関する研究 : 第7報-乱流における流動機構の数値的研究
  • 屈折管内の流れに関する研究-7-乱流における流動機構の数値的研究
  • クッセツカンナイ ノ ナガレ ニカンスルケンキュウ 7 ランリュウ ニ オケル

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Abstract

The dynamic characteristics in the turbulent flow for a two-dimensional bending conduit were determined computationally and the flow mechanisms, especially the energy dissipation mechanisms so important to industry, were discussed. The results obtained were also compared with those in a laminar flow. The turbulence model used included two different equations, one for the kinetic energy of turbulence, k, and the other for its dissipation, ε. The computation was made for five selected miter-bends-three with bending angles Θ of 45°, 90° and 135° and an area ratio λ of 1.0, and two with Θ of 90° and λ's of 1.5 and 2.0, respectively. The Reynolds number Re_<1h>, which refers to the upstream section of the miter-bend was set at 3.75×10^4 for λ of 1.0 or 2.0, and 3.125×10^4 for λ of 0.5 and the computation for Θ of 90° and λ of 1.0 was made at Re_<1h> of 5×10^3, 1×10^4, 2×10^4 and 7.5×10^4. The results can be summarized as follows: 1) The streamlines, velocity distributions, contours of the pressure, vorticity, and kinetic energy of turbulence are shown. 2) The computed velocity distributions were compared with the experimental ones. Both results nearly coincide. 3) The computed terms of the kinetic energy equation and those of the work-energy equation for the mean flow are displayed. The variation of their cross-sectional balances along the conduit are also shown. 4) The total dissipation of energy in turbulent flow DE_<tot>, which is defined by the sum of the dissipation of energy for the mean flow DE_m and that for the kinetic energy of turbulence DE_t or ε, is computed and its aspect of variation for each Θ and λ is discussed. Most of DE_<tot> is occupied by DE_t. DE_m makes a negligible contribution to DE_<tot> except in the neighbourhood of solid walls. 5) Generally, the distortion of the velocity distribution along the center-line of conduit increases as Re_<1h> increases. The contribution of DE_t to DE_<tot> increases as Re_<1h> increased. 6) The inclinations of DE_<tot> and the dissipation of energy in laminar flow DE_l along the conduit coincide qualitatively. In the energy dissipation and transfer processes, the eddy caused by the separation from the convex corner plays a more important part than that from the concave corner whether the flow is turbulent or laminar.

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