arXiv 2606.135962026-06-12physics.flu-dynphysics.soc-ph

平均流偏斜对湍流剪切层的影响。第二部分：实验研究

Effects of mean flow skew on turbulent shear layers. Part II. Experimental investigation

Cornell University（康奈尔大学）；University of Maryland（马里兰大学）

Dipendra Gupta, Vedant Kumar, Johan Larsson, Gregory P. Bewley

备注：: 32 pages, 14 figures

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AI总结：

通过实验方法生成并表征偏斜湍流混合层，发现平均流偏斜使平均和湍流量系统性降低约40%，但基本动力学特性不变，结构参数保持恒定。

摘要：

由两个不同速度的平行流相互作用形成的平面湍流混合层，其研究远多于三维湍流混合层（其中来流偏斜且不平行）。然而，许多实际剪切流是三维的。在此，我们开发并验证了一种实验方法，用于生成和表征偏斜湍流混合层，并量化平均流偏斜如何改变混合层动力学。我们通过在分流板后缘附近安装转向叶片引入平均流的展向偏转，并使用交叉热线风速仪研究流动的下游演化。相对于平面构型，偏斜混合层的平均和湍流量均表现出系统性降低，偏差达到约40%。尽管存在这些定量差异，混合层的基本特征基本保持不变。平均速度剖面在相似性标度下塌缩，剪切层厚度保持近似线性增长，雷诺应力剖面保持其典型的高斯形状。Townsend结构参数（衡量湍流动量输运效率）在平面和偏斜构型之间近似不变，这与偏斜湍流边界层形成对比，后者中类似的平均流偏斜使该参数降低约30%。这些结果表明，平均流偏斜在定量上改变湍流混合层，但对其底层动力学仅产生次要影响。本研究为未来三维自由剪切湍流的研究建立了受控实验框架和经验基准。

英文摘要：

Planar turbulent mixing layers, formed by the interactions of two parallel streams with different velocities, have been studied far more than three dimensional (3D) turbulent mixing layers, in which the incoming streams are skewed, and not parallel. Yet many practical shear flows are 3D. Here, we develop and validate an experimental methodology to generate and characterize skewed turbulent mixing layers and to quantify how mean-flow skew modifies mixing layer dynamics. We introduce skew with a spanwise deflection of the mean flow using turning vanes mounted near the trailing edge of a splitter plate, and we use cross-wire anemometry to investigate the downstream evolution of the flow. Relative to the planar configuration, the skewed mixing layer exhibits systematic reductions in both mean and turbulent quantities, with deviations reaching approximately 40\%. Despite these quantitative differences, the fundamental characteristics of the mixing layer remain largely unchanged. Mean-velocity profiles collapse under similarity scaling, shear-layer thicknesses retain approximately linear downstream growth, and Reynolds-stress profiles preserve their characteristic near-Gaussian form. Townsend's structure parameter, which quantifies the efficiency of turbulent momentum transport, remains approximately invariant between the planar and skewed configurations, in contrast to skewed turbulent boundary layers, wherein comparable mean flow skewing reduces the parameter by approximately 30\%. These results indicate that mean flow skew modifies turbulent mixing layers quantitatively while exerting only a secondary influence on their underlying dynamics. This study establishes a controlled experimental framework and empirical benchmark for future investigations of three-dimensional free-shear turbulence.

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