Experimental and theoretical investigation of the nonmodal growth of steady streaks in a flat plate boundary layer
Experimental and theoretical investigation of the nonmodal growth of steady streaks in a flat plate boundary layer
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DOI：
10.1063/1.1773493
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发表时间：
2004-08
影响因子：
4.6
通讯作者：
J. Fransson;L. Brandt;A. Talamelli;C. Cossu
中科院分区：
文献类型：
--
作者：
J. Fransson;L. Brandt;A. Talamelli;C. Cossu
本文对平板边界层中定常和跨向周期性流向条纹的非模式增长进行了实验和理论研究。稳定的层流条纹是通过固定在平板上的小圆柱形粗糙单元的跨向周期性阵列实验产生的。测量了条纹的流向演化，证明了除粗糙元素附近的一小部分区域外，其他区域的条纹均服从边界层标度。最大可达幅度主要由粗糙度元素的相对高度决定。计算结果与最优和次优边界层条纹的数值模拟结果进行了比较。该理论能够解释最近在实验上可实现的非模式增长和最优微扰理论之间注意到的一些差异。结果表明，壁面法线位置和层流驻留流向涡的扩展是产生条纹的关键因素。不同的实验结果可以用不同的主导条纹产生机制来解释，这些机制可以与几何形状和粗糙度高度与边界层尺度之比有关。
An experimental and theoretical investigation aimed at describing the nonmodal growth of steady and spanwise periodic streamwise streaks in a flat plate boundary layer is presented. Stable laminar streaks are experimentally generated by means of a spanwise periodic array of small cylindrical roughness elements fixed on the plate. The streamwise evolution of the streaks is measured and it is proved that, except in a small region near the roughness elements, they obey the boundary layer scalings. The maximum achievable amplitude is mainly determined by the relative height of the roughness elements. Results are compared with numerical simulations of optimal and suboptimal boundary layer streaks. The theory is able to elucidate some of the discrepancies recently noticed between experimentally realizable nonmodal growth and optimal perturbation theory. The key factor is found to be the wall normal location and the extension of the laminar standing streamwise vortices inducing the streaks. The differences among previous experimental works can be explained by different dominating streak generation mechanisms which can be linked to the geometry and to the ratio between the roughness height and the boundary layer scale.