Structure of high and low shear-stress events in a turbulent boundary layer
Structure of high and low shear-stress events in a turbulent boundary layer
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DOI：
10.1103/physrevfluids.3.014609
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发表时间：
2018-01-19
影响因子：
2.7
通讯作者：
Ganapathisubramani, B.
中科院分区：
文献类型：
--
作者：
Gomit, G.;de Kat, R.;Ganapathisubramani, B.
用粒子图像测速仪(PIV)和壁面剪应力传感器同时测量了雷诺数Re-tau接近4000的平板湍流边界层中与剪应力事件相关的结构。PIV视场沿流向覆盖8个三角洲(其中增量是边界层厚度)，并在壁法向捕获整个边界层。同时，使用跨度阵列的热膜表面摩擦传感器(跨越2个三角洲)进行了捕捉大规模波动的壁面剪应力测量。基于这一测量组合，可以提取条件壁法向和流向速度波动(u和v)以及雷诺切应力(-UV)的组织。速度场的条件平均值是通过将大尺度壁面剪应力波动的直方图分成四个四分位数来计算的，每个四分位数包含25%的出现次数。与直方图的极端四分位数(正和负)相对应的条件事件主要导致与大结构相关的速度剖面的变化和小尺度的调制。对四个四分位数的雷诺剪应力贡献的详细研究表明，在低壁面剪应力事件上方的流动比其他四分位数携带更多的雷诺剪应力。基于速度场的尺度分解，讨论了小尺度和大尺度对观测的贡献。
Simultaneous particle image velocimetry (PIV) and wall-shear-stress sensor measurements were performed to study structures associated with shear-stress events in a flat plate turbulent boundary layer at a Reynolds number Re-tau approximate to 4000. The PIV field of view covers 8 delta (where delta is the boundary layer thickness) along the streamwise direction and captures the entire boundary layer in the wall-normal direction. Simultaneously, wall-shear-stress measurements that capture the large-scale fluctuations were taken using a spanwise array of hot-film skin-friction sensors (spanning 2 delta). Based on this combination of measurements, the organization of the conditional wall-normal and streamwise velocity fluctuations (u and v) and of the Reynolds shear stress (-uv) can be extracted. Conditional averages of the velocity field are computed by dividing the histogram of the large-scale wall-shear-stress fluctuations into four quartiles, each containing 25% of the occurrences. The conditional events corresponding to the extreme quartiles of the histogram (positive and negative) predominantly contribute to a change of velocity profile associated with the large structures and in the modulation of the small scales. A detailed examination of the Reynolds shear-stress contribution related to each of the four quartiles shows that the flow above a low wall-shear-stress event carries a larger amount of Reynolds shear stress than the other quartiles. The contribution of the small and large scales to this observation is discussed based on a scale decomposition of the velocity field.