Title: Spatial Features of Reynolds-Stress Carrying Structures in Turbulent Boundary Layers with Pressure Gradient Show Chinese title

Title: 带有压力梯度的湍流边界层中雷诺应力携带结构的空间特征

Abstract: We investigate the Reynolds-shear-stress carrying structures in the outer layer of non-equilibrium pressure-gradient turbulent boundary layers using four direct numerical simulation databases, two cases of non-equilibrium pressure-gradient boundary layers and two of homogeneous shear turbulence. We examine and compare the spatial organization and shapes of the Reynolds-shear-stress structures, specifically sweeps and ejections, across all cases. The analysis includes five streamwise locations in the boundary layers, varying in pressure-gradient sign, intensity, and upstream history. For the boundary layers, two types of three-dimensional velocity fields are considered: fully spatial fields and spatio-temporal fields using Taylor's frozen turbulence hypothesis. Comparisons of the results indicate that the statistics of sweep and ejection shapes are sensitive to the choice of convection velocity in Taylor's hypothesis. The sweep and ejection shapes are consistent across all flows when their sizes range from 1 to 10 Corrsin length scales, suggesting that mean shear plays a similar role in all cases, driving the formation of Reynolds-shear-stress carrying structures and contributing to turbulence production. Sweeps and ejections of different types form side-by-side pairs, while structures of the same type align in an upstream-downstream configuration. This behavior persists regardless of pressure gradient variations or upstream history, emphasizing the dominant influence of local mean shear. Show Chinese abstract

Abstract: 我们使用四个直接数值模拟数据库研究了非平衡压力梯度湍流边界层外层的雷诺剪切应力携带结构，其中包括两个非平衡压力梯度边界层案例和两个均匀剪切湍流案例。我们检查并比较了所有案例中雷诺剪切应力结构（特别是扫掠和喷射）的空间组织和形状。分析包括边界层中的五个流向位置，这些位置的压力梯度符号、强度和上游历史各不相同。对于边界层，考虑了两种类型的三维速度场：完全空间场和利用泰勒冻结湍流假设的时空场。结果比较表明，扫掠和喷射形状的统计特性对泰勒假设中对流传质速度的选择敏感。当扫掠和喷射的尺寸范围从1到10个Corrsin尺度时，它们的形状在所有流动中都是一致的，这表明平均剪切在所有情况下都起着相似的作用，驱动雷诺剪切应力携带结构的形成，并有助于湍流产生。不同类型的扫掠和喷射形成相邻的对，而同类型结构则以上游-下游配置排列。这种行为在压力梯度变化或上游历史不同的情况下仍然存在，强调了局部平均剪切的主导影响。