Comparison of turbulence structures at large and small drag reduction ratios in turbulent boundary layer of surfactant solutions
Comparison of turbulence structures at large and small drag reduction ratios in turbulent boundary layer of surfactant solutions
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DOI：
10.1080/14685248.2011.560943
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发表时间：
2011-01
影响因子：
1.9
通讯作者：
Shinji Tamano;M. Itoh
中科院分区：
文献类型：
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作者：
Shinji Tamano;M. Itoh
在本研究中，比较了动量-厚度雷诺数Re-θ≃为800时表面活性剂溶液中减阻湍流边界层的湍流结构，以及在溶液温度T=30℃和35℃时，减阻率为34%时表面活性剂溶液中的湍流结构。流向和壁法向速度脉动的象限分析表明，扫掠和抛射事件对雷诺切应力的正贡献与向内相互作用和向外相互作用事件的负贡献相当，因此雷诺切应力几乎为零。此时，象限II和象限IV的最大正贡献和象限I和象限III的最大负贡献与相应壁面附近的水相当，但象限II和象限IV的正贡献区域变窄，象限I和象限III的负贡献区域变宽，雷诺切应力减小。在高活度时，水流方向的速度脉动比水小，但即使在边界层中心附近，除了近壁区也相对较大，而在低活度时，脉动速度矢量几乎平行于壁面。在At，掠过和抛射事件的尺度远大于水的尺度，而涡包的倾角远小于水的倾角。在(x-z)面上，展向湍流脉动被强烈抑制，没有观察到涡旋结构，而在壁面附近，观察到了几个似乎与发夹涡腿的横截面相对应的涡旋结构。在冻结湍流的假设下，发现对于和34%，尽管低速区被遮挡，但高速和低速区是横向排列的。
In this study, turbulence structures of drag-reducing turbulent boundary layers in surfactant solutions at the momentum-thickness Reynolds number Re θ≃800 were compared at large and small drag reduction ratios and 34% at the solution temperature, T=30°C and 35°C. Turbulence statistics and structures were obtained by a two-component laser-Doppler velocimetry (LDV) and particle image velocimetry (PIV) systems for the streamwise and wall-normal (x–y) plane and the streamwise and spanwise (x–z) plane. The quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that at , the positive contribution of sweep and ejection events to the Reynolds shear stress was comparable with the negative contribution of inward-interaction and outward-interaction events, so that the Reynolds shear stress was almost zero. At , the maximum positive contributions of quadrants II and IV and the maximum negative contributions of quadrants I and III were comparable with those of the corresponding water near the wall, but the region of positive contributions in quadrants II and IV became narrower and the region of negative contributions in quadrants I and III became wider, so that the Reynolds shear stress decreased. At , in high activity, the streamwise velocity fluctuations were smaller than those of water but were relatively large even near the center of the boundary layer, in addition to the near-wall region, while in low activity, the fluctuating velocity vectors were almost parallel to the wall. At , the scale of sweep and ejection events was much larger than that of water and the inclination angle of vortex packets at was much smaller than that of water. At , the spanwise turbulence fluctuation was strongly suppressed and vortical structures were not observed on the (x–z) plane, while at , several vortical structures, which seemed to correspond to the cross section of legs of hairpin vortices, were observed near the wall. Under the assumption of frozen turbulence, it was found that for both and 34%, the high- and low-speed regions were aligned laterally, although the low-speed regions at were obscured.