Abstract A direct numerical simulation dataset of a fully developed turbulent Couette-Poiseuille flow is analyzed to investigate the spatial organization of streamwise velocity-fluctuating u-structures on large and very large scales. Instantaneous and statistical flow fields show that negative-u structures with a small scale on a stationary bottom wall grow throughout the centerline due to the continuous positive mean shear, and they penetrate to the opposite moving wall. The development of an initial vortical structure related to negative-u structures on the bottom wall into a large-scale hairpin vortex packet with new hairpin vortices, which are created upstream and close to the wall, is consistent with the auto-generation process in a Poiseuille flow (Zhou et al., J. Fluid Mech., vol. 387, 1999, pp. 353–396). Although the initial vortical structure associated with positive-u structures on the top wall also grows toward the bottom wall, the spatial development of the structure is less coherent with weak strength due to the reduced mean shear near the top wall, resulting in less turbulent energy on the top wall. The continuous growth of the structures from a wall to the opposite wall explains the enhanced wall-normal transport of the streamwise turbulent kinetic energy near the centerline. Finally, an inspection of the time-evolving instantaneous fields and conditional averaged flow fields for the streamwise growth of a very long structure near the centerline exhibits that a streamwise concatenation of adjacent large-scale u-structures creates a very-large-scale structure near the channel centerline.

中文翻译：

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湍流 Couette-Poiseuille 流的直接数值模拟，第 2 部分：大规模和超大规模运动

摘要 对完全发展的库埃特-泊肃叶湍流的直接数值模拟数据集进行了分析，以研究大尺度和超大尺度上的流向速度波动 u 结构的空间组织。瞬时和统计流场表明，由于连续的正平均剪切，在静止底壁上小尺度的负 u 结构在整个中心线上生长，并穿透到相反的移动壁。与底壁上的负 u 结构相关的初始涡结构发展为具有新发夹涡的大型发夹涡包，这些涡在上游和靠近壁处产生，这与 a 中的自动生成过程一致。泊肃叶流（Zhou et al., J. Fluid Mech., vol. 387, 1999, pp. 353–396）。虽然与顶壁正u结构相关的初始涡旋结构也向底壁生长，但由于顶壁附近平均剪切减小，结构空间发展不连贯，强度弱，导致湍流能量减少在顶墙上。结构从壁到相对壁的连续增长解释了中心线附近流动湍流动能的壁法向传输增强。最后，对中心线附近一个非常长的结构的流向增长的时间演化瞬时场和条件平均流场的检查表明，相邻大型 u 结构的流向串联在附近创建了一个非常大的结构。通道中心线。