权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Clarification of Drag-Reduction-Mechanism over a Riblet surface and Exploration of Geometry of Riblet

肋条表面减阻机理的阐明及肋条几何形状的探索

基本信息

批准号：
06650200
负责人：
YAMASHITA Shintaro
金额：
$ 1.28万
依托单位：
GIFU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06650200/
关键词：
Riblet Skin-Friction Drag Reduction Wall Jet Turbulence

项目摘要

This research is intended to investigate the effect that riblets reduce skin-friction in a wall jet and to make it clear that this is due to modify the turbulent structure in the near wall jet. So far, it is cleared that the local skin-friction estimated from the mean velocity profiles indicates the reduction rate of the drag.The principal results got for the term of project concerned are as follows.1.The larger size riblet surface was made and it was recognized that the local skin-friction estimated from the mean velocity profiles indicates larger reduction ratio at the larger position than the former non-dimensional riblet width.2.In the region where the drug reduction due to the riblets yields.the probability density functions for fluctuating velocity near the wall show approximately Gaussian distribution.3.From the analysis of the VITA technique, the bursting wave is observed even in the wall jet, however the time scale is ten times as long as that in turbulent boundary layr.The results of the four-quadrant method exhibit that the mechanism of generating to the Reynolds stress is become weak due to the riblets.4.The correlation length of the fluctuating velocity increase in the x-direction and z-direction due to the riblets. The integral scales near the wall in spanwise direction above the riblet surface are larger in comparison with the flat surface and the spanwise scales of large eddy are large.5.The spanwise spectrum in the wall jets increase as the wave length increasing within the inner layr. This shows the difference from the turbulent structure in the boundary layr and a discrepancy of the riblet scale that the maximum reduction ratio occurred is attributed to the difference in the turbulent structure like this.6.The results in the direct method in a wall jet on the flat surface belong to the range of the scatter the indirect meathod by the other research worker and these data are reliable.

这项研究的目的是研究肋条减少壁射流中的表面摩擦的效果，并明确这是由于改变了近壁射流中的湍流结构。到目前为止，已经明确，根据平均速度分布估计的局部皮肤摩擦力表明了阻力的减小率。有关项目期间获得的主要结果如下：1.制作了更大尺寸的沟槽表面，并认识到根据平均速度分布估计的局部皮肤摩擦力在比以前的无量纲沟槽宽度更大的位置处表明了更大的减小率。2.在药物存在的区域壁面附近脉动速度的概率密度函数近似呈高斯分布。3.从VITA技术的分析来看，即使在壁面射流中也能观察到爆裂波，但时间尺度是湍流边界层中的10倍。四象限法的结果表明，由于 4. 肋条引起的 x 方向和 z 方向脉动速度增加的相关长度。肋条表面上方翼展方向近壁面的积分尺度较平面更大,大涡的展向尺度也较大。5.壁面射流的翼展谱随内层波长的增加而增大。这表明与边界层湍流结构的差异以及最大减速比出现的肋状尺度的差异是由于这种湍流结构的差异造成的。 6.平面壁射流直接法的结果属于其他研究人员散射间接法的范围，这些数据是可靠的。