Effect of flow around a wall-mounted 2D square cylinder on WSS in a TBL
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摘要: 利用TR–PIV与平行双丝热线，对平板边界层内的贴壁二维方柱绕流流场和壁面摩擦应力的关联进行了实验研究。主要关注方柱下游大尺度流动结构的运动对近壁面流向平均速度零点处摩擦应力的影响（基于方柱宽度与来流风速定义的雷诺数固定为1.1 × 104）。研究表明，贴壁二维方柱绕流产生了2种典型的流动结构：一为向壁面靠近并接触壁面的近壁流动结构，本文称“I涡”；一为平行壁面沿流向运动的流动结构，本文称“Ⅱ涡”。Ⅰ涡、Ⅱ涡的出现改变了壁面附近流动速度的大小和方向，影响了测点壁面摩擦应力：增大了流向速度梯度，导致摩擦应力陡增；减小了流向速度梯度，导致摩擦应力锐减；改变了摩擦应力方向。本文研究结果可为理解表面冲蚀、污染物聚集、近壁面湍流耗散等问题的机理提供参考。Abstract: In this paper, the effect of flow around a wall-mounted 2D square cylinder on WSS (Wall Shear Stress) in a TBL (Turbulent Boundary Layer) is studied using TR–PIV and hot wires. The Reynolds number, defined by the cylinder width and the free stream velocity, is fixed at 1.1 × 104. There exist two types of large-scale flow structures, i.e., vortex I which denotes those moving towards the wall, and vortex II which denotes those moving downstream. The flow structures have significant effects on the flow and WSS: increasing the streamwise velocity gradient that results in a sharply increased WSS; reducing the streamwise velocity gradient that results in a sharply decreased WSS; and changing the WSS direction. The study is helpful to understand the physics of surface erosion, pollutant accumulation, flow energy loss, etc.
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Key words:
- wall-mounted 2D cylinder /
- wall shear stress /
- turbulent boundary layer /
- flow structure
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图 2 平板湍流边界层流向平均速度剖面
Figure 2. Profile of time-averaged streamwise velocity of flat plate TBL
图 3 贴壁二维方柱下游流场PIV测量示意图
Figure 3. Diagram of PIV measurement of flow field downstream of the 2D wall-mounted square cylinder
图 7 不同雷诺数下平板湍流边界层平均摩擦应力测量结果
Figure 7. Results of time-averaged shear stress in flat plate TBL at different Reynolds numbers
图 8 贴壁二维方柱下游平板摩擦应力测量示意图
Figure 8. Diagram of WSS measurement downstream of the wall-mounted 2D square cylinder
图 9 贴壁二维方柱下游流场统计特征量分布云图
Figure 9. Contour of statistical values of flow field downstream of the wall-mounted 2D square cylinder
图 10 x/D = 7处流动雷诺剪应力沿法向分布
Figure 10. Distribution of Reynolds shear stress of flow along normal direction at x/D = 7
图 11 贴壁二维方柱下游流动结构运动过程，4图为连续时间序列，时间差1 ms
Figure 11. Motion process of flow structure downstream of the wall mounted 2D square cylinder, where the four figures are continuous time series with interval of 1 ms
图 12 贴壁二维方柱下游流动结构运动过程，4图为连续时间序列，时间差2 ms
Figure 12. Motion process of flow structure downstream of the wall mounted 2D square cylinder, where the four figures are continuous time series with interval of 2 ms
图 13 流动结构分裂过程中的涡旋强度等值线图
Figure 13. Vorticity intensity contour of flow structure during splitting
图 14 贴壁二维方柱下游壁面摩擦应力统计值沿流向分布
Figure 14. Distribution of statistical value of WSS along the flow direction downstream of the wall-mounted 2D square cylinder
图 15 贴壁二维方柱下游某些时间段内的瞬时流场
Figure 15. Instantaneous flow field downstream of wall-mounted 2D square cylinder during certain time periods
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