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A Study on Drag Reduction Mechanism on the Basis of Quasi-Coherent Structures in Wall Turbulence

基于准相干结构的壁面湍流减阻机理研究

基本信息

批准号：
04452140
负责人：
KASAGI Nobuhide
金额：
$ 3.97万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04452140/
关键词：
Turbulence Wall shear stress Drag reduction Coherent Structure Riblet Particle tracking velocimetry

项目摘要

The structure of turbulent flow field along a riblet surface was investigated with the aid of a three-dimensional particle tracking velocimetry (3-D PTV). The statistics of all three velocity components were measured and compared with those above a smooth wall. Under a drag reducing condition, all the turbulent velocity fluctuations and the Reynolds shear stress were decreased near the riblet surface, although the flow characteristics in most of the flow field were quite similar to those above the smooth wall. It was also found that the redistribution mechanism of the turbulent kinetic energy from the streamwise component to the spanwise one was considerably suppressed in the region above the riblet valley. On the other hand, under a neutral drag condition, a cross-stream secondary flow was apparent near the ribs ; as large as 0.8% of the maximum velocity.Moreover, a quadrant analysis was applied to the velocity database presently obtained and the near-wall quasi-coherent structures, which are responsible for the Reynolds shear stress are examined by using a conditional sampling technique. The quasi-streamwise vortices and streaky structures were found also above the riblet surface. Under the drag reducing condition, streamwise vortices have almost same characteristics as those above the smooth wall. The cores of vortex are displaced from the riblet surface and these vortices are free from the strong interaction with the ribs. The spatial length scales of near-wall streaky structures are unchanged in this case. On the other hand, sweep motions penetrate into the riblet valley under the drag increasing condition and the vortex structures are markedly affected by the ribs. It is also found that the streamwise persistence of the streaky structures are considerably decreased in this case.

利用三维粒子跟踪测速仪（3-D PTV）研究了沟槽表面沿着湍流流场的结构。测量了所有三个速度分量的统计数据，并与光滑壁以上的统计数据进行了比较。在减阻条件下，尽管大部分流场的流动特性与光滑壁面上的流动特性相似，但沟槽表面附近的湍流速度脉动和雷诺切应力都有所降低。同时还发现，在脊谷以上的区域，湍流动能从流向分量向展向分量的再分配机制被显著抑制。另一方面，在中性阻力条件下，横流二次流是明显的肋附近，大的0.8%的最大速度。此外，象限分析应用到目前获得的速度数据库和近壁准相干结构，这是负责雷诺剪应力的检查通过使用条件抽样技术。在沟槽表面上方也发现了准流向涡和条纹结构。在减阻条件下，流向涡具有与光滑壁面上方涡几乎相同的特征。涡核从肋表面位移，这些涡不受肋的强相互作用。在这种情况下，近壁条纹结构的空间长度尺度是不变的。另一方面，在增阻条件下，后掠运动穿透到肋谷，肋对涡结构有显著影响。它还发现，在这种情况下，条纹结构的流向持久性大大降低。