Statistical structure of momentum sources and sinks in the outer region of a turbulent boundary layer
Statistical structure of momentum sources and sinks in the outer region of a turbulent boundary layer
复制标题
湍流边界层外部区域动量源和汇的统计结构
DOI：
--
复制
发表时间：
2008
影响因子：
3.7
通讯作者：
B. Ganapathisubramani
中科院分区：
文献类型：
--
作者：
B. Ganapathisubramani
利用两个壁面法线位置(x2/δ=0.1和0.5，其中x2为壁面法线位置，x2为壁面法线位置，δ为边界层厚度)的双平面粒子图像测速数据，研究了湍流边界层中动量源和动量汇(T>；0和T<；0；其中T是兰姆矢量的流向分量)的空间结构。T的两点关联表明，源运动的大小相对不变，而汇运动的大小随着壁法向距离的增加而增大。下沉运动的相对强度在远离墙体时也会增加。通过计算T与速度分量的互相关关系，探索了源/汇运动附近的速度场。类震源运动与拉长的低动量带相关，这些拉长的低动量带内嵌有上升区，在这些低动量带沿展向弯曲的地区似乎最强。动量汇似乎位于低速区域，而低速区域位于较大的高动量区域内。速度涨落在汇附近的象限之间经历快速转换(即流向和壁法向速度涨落都改变符号)。在x2/δ=0.5时，波动改变符号的长度标度比在x2/δ=0.1时大得多。
The spatial structure of momentum sources and sinks (T > 0 and T < 0; where T is the streamwise component of the Lamb vector) is examined in a turbulent boundary layer by using dual-plane particle image velocimetry data obtained in streamwise–spanwise planes at two wall-normal locations (x2/δ = 0.1 and 0.5, where x2 is the wall-normal location and δ is the boundary layer thickness). Two-point correlations of T indicate that the size of source motions remains relatively constant while the size of sink motions increases with increasing wall-normal distance. The relative strength of sink motions also increases away from the wall. The velocity field in the vicinity of source/sink motions was explored by computing cross-correlations of T with the velocity components. Source-like motions are correlated with elongated low-momentum zones that possess regions of upwash embedded within them and appear to be the strongest in areas where these low-momentum zones meander in the spanwise direction. Momentum sinks appear to be located within low-speed regions that are within larger high-momentum zones. The velocity fluctuations undergo rapid transitions between quadrants in the vicinity of sinks (i.e. both streamwise and wall-normal velocity fluctuations change sign). The length scales, over which the fluctuations change sign, are much larger at x2/δ = 0.5 than at x2/δ = 0.1.