円柱冷却によって低レイノルズ数で発生する冷却渦列 : 冷却後流の時間変動および円柱表面値に与える流体種類の影響(熱工学,内燃機関,動力など)

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The cooled wake in mercury, air, or water at the Reynolds number 44 is analyzed numerically. Effects of fluid kinds on the time-dependence and the cylinder surface values in the cooled wake and the cooled vortex street are elucidated as follows: (1) The streamfunction oscillates with the constant amplitude in both the Karman vortex street in any fluid and the cooled vortex street in mercury and air, but oscillates with the amplitude pluraling in both the transitional process to the cooled vortex street in any fluid and the cooled vortex street in water. (2) The oscillation type in the cooled vortex street depends on the Prandtl number Pr. The oscillation has the constant amplitude at the low and moderate Pr as mercury and air, but, has the amplitude pluraling at the high Pr as water. (3) The distribution and the time-dependence of the local and mean coefficients of wall shear stress c_f, C_f and the local and mean Nusselt numbers Nu, Nu_m are elucidated in the cooled wake in mercury, air and water. (4) In the cooled wake in any fluid, the negative buoyancy makes the Strouhal number St, mean coefficient of wall shear stress C_f, mean Nusselt number Nu_m, and vortex speed U_v small, and the amplitude of wake oscillation large. The cooled vortex street in any fluid oscillates with the frequency less than the Karman vortex street. (5) The St number in any kind of fluid and the C_f and Nu_m numbers in air are decreased suddenly in the transitional process. The decrease behavior of St is different among fluid kinds. (6) The sudden change is an unstable-like phenomenon, and the transitional region with the sudden change is the unstable-like state. The streamfunction oscillation has the amplitude pluraling in the unstable-like state, and has the constant amplitude in the stable-like state.
2009-01-25

著者

能登勝久
能登熱流体科学研究所

円柱冷却によって低レイノルズ数で発生する冷却渦列 : 冷却後流の時間変動および円柱表面値に与える流体種類の影響(熱工学,内燃機関,動力など)

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