1995 Fiscal Year Final Research Report Summary
Clarification of Drag-Reduction-Mechanism over a Riblet surface and Exploration of Geometry of Riblet
| Project/Area Number |
06650200
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Fluid engineering
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| Research Institution | GIFU UNIVERSITY |
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Principal Investigator |
YAMASHITA Shintaro Gifu University Faculty of Engineering, Mechanical engineering, Professor, 工学部, 教授 (20023236)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Yoshihiro Suzuka College of Technology, Mechanical Engineering, Assistant Professor, 機械工学科, 講師 (00176455)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Riblet / Skin-Friction / Drag Reduction / Wall Jet / Turbulence |
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| Research Abstract |
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.
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