界面活性剤水溶液の抵抗低減乱流境界層における乱れ構造 : 抵抗低減率の異なる流れ場の比較(流体工学,流体機械)

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  • Turbulence Structures in Drag-Reducing Turbulent Boundary Layer of Surfactant Solution : Comparison between Flow Fields of Large and Small Drag Reduction Ratios(Fluids Engineering)
  • 界面活性剤水溶液の抵抗低減乱流境界層における乱れ構造(抵抗低減率の異なる流れ場の比較)
  • カイメン カッセイザイ スイヨウエキ ノ テイコウ テイゲン ランリュウ キョウカイソウ ニ オケル ミダレ コウゾウ テイコウ テイゲンリツ ノ コトナル ナガレバ ノ ヒカク

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In this study, turbulence structures of the drag-reducing turbulent boundary layer in the surfactant solution at the momentum-thickness Reynolds number Re_θ≃800 were compared between at the large and small drag reduction ratios. Turbulence statistics and structures were obtained by the two-component LDV system and the PIV system for the streamwise and wall-normal (x-y) section and the streamwise and spanwise (x-z) section. The surfactant solution used here was a mixture of cetyltrimethyl ammonium chloride (CTAC) with sodium salicylate as counterion, which was dissolved in tap water. The concentration of CTAC was 65ppm, and the molar ratio of counterion to CTAC was two. The drag reduction ratios DR=78% and 34% were obtained at the solution temperature T=30℃ and 35℃, respectively. The quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that at DR=78%, the positive contribution of the sweep and ejection events to the Reynolds shear stress was comparable with the negative contribution of the inward-interaction and outward-interaction events, so that the Reynolds shear stress was almost zero. At DR=78%, both streamwise and spanwise velocity fluctuations were attenuated largely across the turbulent boundary layer. On the other hand, at DR=34%, turbulence structures were similar to those of water as a whole, although the scale was larger compared to the water.

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