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.

这项研究旨在调查开裂物减少壁式射流中的皮肤摩擦的影响，并明确表明这是由于修改近壁喷气机中的湍流结构所致。到目前为止，可以清楚地看出，从平均速度曲线中估计的局部皮肤摩擦表明，拖拉的率降低。相关项目期限的主要结果如下。1。1.进行了较大的riblet表面，并且已经确认了局部皮肤 - 从平均速度较大的位置估计的局部皮肤均比以前的速度较大的位置。由于裂缝而导致的减少。墙壁附近波动速度的概率密度函数大致显示出大约高斯的分布。3。从VITA技术的分析中，即使在壁式射流中也观察到爆裂波，但是时间尺度是十倍，但是只要在湍流中呈湍流，即在湍流中均可出现的四个Quadrant方法的结果。 RIBLET。4。由于河豚而引起的X方向和Z方向的波动速度的相关长度增加。与平坦的表面相比，裂缝表面上方的侧面方向靠近壁附近的整体尺度与大涡流的跨度尺度大。这表明了边界线路中的湍流结构的差异以及最大还原比的riblet量表的差异归因于这样的湍流结构的差异。6。6。在平坦表面上的壁射流中的直接方法属于散点范围的其他研究工作者的散布范围，其他研究工作者是其他研究工作人员的其他研究工作者，这些数据是由其他研究工作者和这些数据可靠的。