AN EXPERIMENTAL STUDY ON 1/f^<tx> STRUCTRE AND ENTRAINMENT IN TURBULENT BOUNDARY LAYER

湍流边界层1/f^<tx>结构和夹带的实验研究

基本信息

批准号：
13650182
负责人：
MOCHIZUKI Shinsuke
金额：
$ 2.3万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650182/
关键词：
Turbulent Boundary Layer Entrainment Coherent Structure Fractals Equilibrium Boundary Layer

项目摘要

In the present study, entrainment mechanisms associated with large scale eddies in turbulent boundary layers has been investigated in terms of 1/f^<tx> intermittent nature defined in fractals. The experiment has been made in a flat plate boundary layer and a self-preserving boundary layer developed under power-law variation of the free-stream. The free-stream is decelerating with x^<-0.188> for the self-preserving boundary layer, thus the boundary layer is subjected to a mild adverse pressure gradient.A new direct measurement device for the local wall shear stress has been developed and applied in the present experimental study. The measurement device has 20mm circular friction surface and zero-displacement circuit that keeps the floating element at initial position. Application of the new device to the flat plate boundary layer proves that the wall shear stress can be obtained experimentally with sufficiently high accuracy and reliability.In both the boundary layers, the mean velocity profile near the wall can be reasonably expressed in the logarithmic mean velocity profile with Karman constant of 0.41 and additive constant of 5.0. Strength of wake component in the outer layer mean velocity profile is strongly enlarged by the adverse pressure gradient. The triple velocity products, which mean turbulence diffusion of Reynolds shear stresses and turbulent intensity, become greater in magnitude of absolute values.The outer layer intermittent nature has been investigated by conditional sampling technique that is applied to recognize turbulent and non-turbulent zones. Two-point double velocity correlation functions were calculated for turbulent zone and non-turbulent zone, respectively. A large scale streamwise vortical motion is expected in turbulent bulge and spanwise size of the vortical motion is squeezed by the adverse pressure gradient. The probability of streamwise interval of turbulent can be successfully explained by power-law functions.

在本研究中，已经根据分形定义的1/f^<tx>间歇性质研究了与湍流边界层中与大规模涡流相关的夹带机制。该实验是在平板边界层中进行的，并且在自由流的幂律变化下开发了自我保护的边界层。对于自我保护的边界层，自由流正在用X^<-0.188>减速，因此边界层受到轻度的不良压力梯度。在本实验研究中。该测量设备具有20mm的圆形摩擦表面和零置换电路，可将浮动元件保持在初始位置。新设备在平板边界层中的应用证明，可以以足够高的精度和可靠性在实验中获得壁剪应力。在两个边界层中，壁附近的平均速度曲线可以在对数平均速度中合理地表达Karman常数为0.41，添加剂常数为5.0。外层中的尾流组件的强度通过不利压力梯度强烈扩大。三重速度产物意味着雷诺的湍流扩散剪切应力和湍流强度在绝对值的幅度上变得更大。通过有条件的采样技术研究了外层间歇性的性质，该技术用于识别湍流和非扰动区域。分别针对湍流区和非扰动区计算了两点双速度相关函数。预计在湍流凸起中有大规模的流向涡旋运动，并且涡流运动的跨度大小被不利压力梯度挤压。湍流间隔的流向间隔的概率可以通过幂律函数成功解释。