Recent experimental studies on homogeneous curved shear flow have shown that the imposition of strong mean flow curvature can cause a reversal of the turbulent shear stress, giving it the same sign as the gradient of mean velocity. Measurements of the coherence spectrum for these flows has revealed that this reversal is not uniform across all scales, and that eddies of different sizes can have opposite orientations and transport momentum in opposite directions. To evaluate the influence of linear mechanisms in the shear stress reversal a ‘‘rapid distortion’’ type of model was applied to those flows which demonstrated this phenomenon. The model predicts that flow curvature causes a periodic modulation of the structure of sheared turbulence, and that the sign of the shear stress reverses because of these oscillations. The period of the modulation, in terms of the total strain, was found to decrease as the turning rate increases relative to the shearing rate. For those flows which showed a reversal of the shear stress, the range of experimental observation was only a fraction of the predicted period, but interpreting the observed development as a portion of an oscillation the measurements were found to be qualitatively similar to the predictions of the linear theory. In cases of stronger turbulence a self‐preserving structure developed, before the shear stress could reverse, and the measurements deviated significantly from the predictions.

中文翻译：

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线性湍流在剪切湍流调节过程中的影响

均匀弯曲的最新实验研究 剪切流 表明强加了卑鄙的手段 流 曲率可能会导致 湍流的 剪切应力，使其与平均速度的梯度相同。 测量 的 连贯性 这些频谱 流 揭示了这种逆转并非在所有范围内都是统一的，并且 涡流不同大小的物体可以具有相反的方向，并且可以在相反的方向上传输动量。为了评估线性机制在剪切应力反转中的影响，一种“快速变形”类型的模型 应用于那些 流证明了这种现象。的模型 预言 流 曲率引起剪切结构的周期性调制 湍流由于这些振荡，剪切应力的符号反转。发现相对于剪切速率，随着总旋转速率的增加，调制周期以总应变的形式减小。对于那些流 它显示了剪切应力的逆转，实验观察的范围只是预测周期的一小部分，但将观察到的发展解释为振荡的一部分。 测量被发现在质量上与线性理论的预测相似。在更强的情况下湍流 在剪切应力可以逆转之前，形成了一种自保持结构， 测量 大大偏离了预测。