Characteristics of large-scale and superstructure motions in a turbulent boundary layer overlying complex roughness
Characteristics of large-scale and superstructure motions in a turbulent boundary layer overlying complex roughness
复制标题
复杂粗糙度上的湍流边界层中大尺度和上层结构运动的特征
DOI：
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发表时间：
2019
影响因子：
1.9
通讯作者：
K. Christensen
中科院分区：
文献类型：
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作者：
J. Barros;K. Christensen
摘要：使用壁法向翼展平面中的高帧率立体粒子图像测速测量来探索复杂粗糙地形上湍流的结构属性。所考虑的粗糙度是从因异物沉积而损坏的涡轮叶片复制而来的，并且包含以高度不规则方式排列的各种地形尺度。 Barros 和 Christensen 先前的结果 [粗糙壁边界层中湍流二次流的观察。流体机械学报。 2014;748]揭示了流动中强烈的展向不均匀性，归因于粗糙度引起的湍流二次流的形成，这是由平均流中翼展方向交替的低动量流路径和高动量流路径（分别为HMP和LMP）识别的，以增强的雷诺应力和湍流动能为标志。本文提出的固定壁法线位置处的流向速度的频谱也显示出对展向位置的强烈依赖性。特别是，粗糙度促进了大尺度和小尺度运动（与非常大尺度的运动相反）的能量含量的增强。根据展向位置，预乘光谱突出显示了由于与光滑壁流相比的粗糙度而导致的超大规模运动（上部结构）的能量含量的显着变化。值得注意的是，在 LMP 中，TKE 和 RSS 内容都向更短的流向尺度转变，而在 HMP 中发现影响较小。
ABSTRACT The structural attributes of turbulent flow over a complex roughness topography are explored using high-frame-rate stereo particle-image velocimetry measurements in the wall-normal–spanwise plane. The roughness under consideration was replicated from a turbine blade damaged by deposition of foreign materials and contains a broad range of topographical scales arranged in a highly irregular manner. Previous results from Barros and Christensen [Observations of turbulent secondary flows in a rough-wall boundary layer. J Fluid Mech. 2014;748] revealed strong spanwise heterogeneity in the flow attributed to the formation of roughness-induced turbulent secondary flows identified by spanwise-alternating low- and high-momentum flow pathways (HMP & LMP, respectively) in the mean flow marked by enhanced Reynolds stresses and turbulent kinetic energy. Frequency spectra of streamwise velocity at fixed wall-normal location presented herein also display strong dependence on spanwise position. In particular, the roughness promotes enhanced energy content of the large-scale and smaller-scale motions (as opposed to very-large-scale ones). Depending on spanwise position, pre-multiplied spectra highlight significant modification of the energy content of the very large-scale motions (superstructures) due to roughness compared to smooth-wall flow. Of note, a shift in both TKE and RSS content to shorter streamwise scales at an LMP was noted, while less of an impact was found coincident with an HMP.