界面活性剤水溶液の乱流境界層における速度場計測(流体工学,流体機械)

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The influence of a drag-reducing surfactant on a zero pressure gradient turbulent boundary layer was investigated using a two-component LDV system. LDV measurements were made for four different momentum thickness Reynolds numbers, R_θ(=U_eθ/ν)=357, 444, 535 and 601, where U_e, θ and ν are the free-stream velocity, momentum thickness and kinematic viscosity, respectively. The amount of drag reduction is from 25.6 to 62.6% when compared to a water flow at the same position and free-stream velocity. The shape factor H(=δ*/θ) increases with increasing drag reduction, where δ* is the displacement thickness. The mean velocity distribution in wall-coordinates indicates the existence of the elastic layer in addition to the standard logarithmic region. It is found that the streamwise turbulence intensity distribution has the additional maximum near the center of the boundary layer, where the solution is not locally in SIS (Shear Induced State) due to the effect of mixing of the potential and turbulent flows. The location of additional maximum of streamwise turbulence intensity is corresponding to the location at which the skewness factor of streamwise turbulent fluctuation is zero. The wall-normal turbulence intensity of the surfactant solution is much smaller than that of water and is almost constant across the boundary layer. Reynolds shear stress distribution does not show the definite maximum near the wall, while it reveals the maximum near the center of the boundary layer. It is also found that the skewness and flatness factors of the wall-normal turbulent fluctuation are almost constant near the outer edge of turbulent boundary layer in the surfactant solution.
2004-05-25

界面活性剤水溶液の乱流境界層における速度場計測(流体工学,流体機械)

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