Spatial evolution of the turbulent/turbulent interface geometry in a cylinder wake
Spatial evolution of the turbulent/turbulent interface geometry in a cylinder wake
复制标题
DOI：
10.1017/jfm.2023.547
复制
发表时间：
2023-01
影响因子：
3.7
通讯作者：
Jiangang Chen;O. Buxton
中科院分区：
文献类型：
--
作者：
Jiangang Chen;O. Buxton
摘要本研究旨在研究圆柱尾流中湍流/湍流界面（TTI）几何特征的空间演化。尾迹暴露在不同的湍流背景中，其中湍流强度和积分长度尺度是独立变化的，并与湍流/非湍流界面（TNTI）进行了比较。湍流尾迹以高施密特数（$Sc$）标量标记，采用平面激光诱导荧光实验捕捉了尾迹与环境流在$x/d = 5 ~ 40范围内的界面，其中$x$为距圆柱体中心的顺流坐标，$d$为圆柱体直径。研究发现，TTI通常比TNTI向周围气流传播得更快。在$x/d \约15$处发现了界面扩展的过渡区域，之后界面的传播速度比之前（上游）慢，并且TNTI和TTI的平均界面位置都与局部尾流半宽有关。由于流动中存在的大规模相干运动的影响，TNTI和TTI的位置在近尾迹处都具有非高斯概率密度函数（pdf）。再往下游，在大尺度相干运动消散后，TNTI位置的PDF确实变成高斯分布。我们首次探索了TTI“粗糙度”的空间变化，通过分形维数量化，从近场到远场。背景流的长度尺度对近尾迹的TTI分形维数有深远的影响，而湍流强度仅对更下游的分形维数有重要影响。
Abstract This study aims to examine the spatial evolution of the geometrical features of the turbulent/turbulent interface (TTI) in a cylinder wake. The wake is exposed to various turbulent backgrounds in which the turbulence intensity and the integral length scale are varied independently, and comparisons to a turbulent/non-turbulent interface (TNTI) are drawn. The turbulent wake was marked with a high Schmidt number ($Sc$) scalar, and a planar laser induced fluorescence experiment was carried out to capture the interface between the wake and the ambient flow from $x/d = 5$ to 40, where $x$ is the streamwise coordinate from the centre of the cylinder, and $d$ is the cylinder's diameter. It is found that the TTI generally spreads faster towards the ambient flow than the TNTI. A transition region of the interfaces’ spreading is found at $x/d \approx 15$, after which the interfaces propagate at a slower rate than previously (upstream), and the mean interface positions of both the TNTI and TTI scale with the local wake half-width. The locations of both the TNTI and TTI have non-Gaussian probability density functions (PDFs) in the near wake because of the influence of the large-scale coherent motions present within the flow. Further downstream, after the large-scale coherent motions have dissipated, the TNTI position PDF does become Gaussian. For the first time, we explore the spatial variation of the ‘roughness’ of the TTI, quantified via the fractal dimension, from near field to far field. The length scale in the background flow has a profound effect on the TTI fractal dimension in the near wake, whilst the turbulence intensity becomes important only for the fractal dimension farther downstream.