湍流通道流中柯尔莫哥洛夫尺度纤维优先排列的实验与数值研究
Experimental and numerical investigation on preferential alignment of Kolmogorov-size fibers in turbulent channel flow
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中文总结 AI 辅助
研究湍流通道流中柯尔莫哥洛夫尺度纤维优先排列，通过实验测量与数值模拟相结合，利用时间分辨体积测量重建纤维轨迹及估计速度梯度张量，发现纤维优先与涡度方向排列，与模拟总体吻合良好，高雷诺数下有偏差。
中文摘要 AI 辅助
我们对摩擦雷诺数\(\mathit{Re}_{\tau}=300\)和\(550\)的湍流通道流中柯尔莫哥洛夫尺度、高纵横比纤维的优先排列进行了实验与数值相结合的研究。在维也纳工业大学湍流水槽中进行时间分辨体积测量，以同时跟踪纤维和周围示踪粒子，从而重建纤维轨迹并对局部速度梯度张量进行粗粒度估计。通过对包含扁长椭球体的通道流进行直接数值模拟提供参考点粒子描述。分析聚焦于通道核心，实验数据恢复了涡度与中间应变率特征向量的典型排列，支持了重建的速度梯度张量的可靠性。我们表明纤维优先与局部涡度方向排列，同时观察到与应变特征向量有较弱但仍非随机的排列。通过左柯西－格林张量测量沿纤维轨迹的有限时间变形，进一步表明最强排列发生在拉格朗日拉伸的主方向。与直接数值模拟的比较总体吻合良好，但在较高雷诺数下的偏差表明有限尺寸滤波效应增加。
英文摘要
We present a combined experimental and numerical investigation of the preferential alignment of Kolmogorov-size, high-aspect-ratio fibers in turbulent channel flow at friction Reynolds numbers $\mathit{Re}_τ=300$ and $550$. Time-resolved volumetric measurements in the TU Wien Turbulent Water Channel are used to simultaneously track fibers and surrounding tracer particles, enabling the reconstruction of fiber trajectories together with a coarse-grained estimate of the local velocity-gradient tensor (VGT). Complementary direct numerical simulations (DNS) of channel flow laden with prolate ellipsoids provide a reference point-particle description. The analysis focuses on the channel core, where the experimental data recover the canonical alignment of vorticity with the intermediate strain-rate eigenvector, thereby supporting the reliability of the reconstructed VGT. We show that fibers preferentially align with the local vorticity direction, while weaker but still non-random alignments are observed with the strain eigenvectors. By measuring finite-time deformation along fiber trajectories through the left Cauchy--Green tensor, we further show that the strongest alignment occurs with the leading principal direction of Lagrangian stretching. The comparison with DNS shows overall good agreement, while deviations at higher Reynolds number suggest increasing finite-size filtering effects.
