Inner–outer interactions of large-scale structures in turbulent channel flow
Inner–outer interactions of large-scale structures in turbulent channel flow
复制标题
DOI：
10.1017/jfm.2016.3
复制
发表时间：
2016-02
影响因子：
3.7
通讯作者：
Jinyul Hwang;Jin Lee;H. Sung;T. Zaki
中科院分区：
文献类型：
--
作者：
Jinyul Hwang;Jin Lee;H. Sung;T. Zaki
湍流通道流动的直接数值模拟数据（$Re_{{\it\tau}}=930$）用于研究流向速度波动的长运动统计（$u$），以及这些结构与近壁扰动的相互作用，这是由它们相关的大尺度环流促进的。在日志层中，与正的$u$结构相比，负的$u$结构被组织成更长的流向范围（${>}3{\it\delta}$）。在墙附近，负- $u$结构的足迹相对于正- $u$结构的足迹相对狭窄。这种差异是由于足迹附近相反的展向运动造成的，这些运动要么是聚集的，要么是分散的，这取决于外部滚动单元的循环。足迹的条件采样表明，高速结构的色散运动显著增强了展向速度波动（$w$）。另一方面，负- $u$结构的近壁聚集运动产生相对较弱的$w$但强烈的负- $u$区域，部分原因是近壁条纹的跨向集体迁移。在外部长尺度合并期间，负- $u$上升井的集中近壁区域-利用合并过程的统计分析证明了这一效应。这导致下游负$u$结构的对流速度降低，从而促进与上游负结构的合并。这些自上而下和自下而上的相互作用增强了长负$u$结构在log区域的空间相干性。
Direct numerical simulation data of turbulent channel flow ( $Re_{{\it\tau}}=930$ ) are used to investigate the statistics of long motions of streamwise velocity fluctuations ( $u$ ), and the interaction of these structures with the near-wall disturbances, which is facilitated by their associated large-scale circulations. In the log layer, the negative- $u$ structures are organized into longer streamwise extent ( ${>}3{\it\delta}$ ) in comparison to the positive- $u$ counterparts. Near the wall, the footprint of negative- $u$ structures is relatively narrow in comparison to the footprint of positive- $u$ structures. This difference is due to the opposite spanwise motions in the vicinity of the footprints, which are either congregative or dispersive depending on the circulation of the outer roll cells. Conditional sampling of the footprints shows that the spanwise velocity fluctuations ( $w$ ) are significantly enhanced by the dispersive motions of high-speed structures. On the other hand, the near-wall congregative motions of negative- $u$ structures generate relatively weak $w$ but intense negative- $u$ regions due, in part, to the spanwise collective migration of near-wall streaks. The concentrated near-wall regions of negative- $u$ upwell during the merging of the outer long scales – an effect that is demonstrated using statistical analysis of the merging process. This leads to a reduction of the convection speed of downstream negative- $u$ structures and thus promotes the merging with upstream ones. These top-down and bottom-up interactions enhance the spatial coherence of long negative- $u$ structures in the log region.