| Project/Area Number |
17560141
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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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 & Systems Eng., Professor, 工学部, 教授 (20023236)
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| Co-Investigator(Kenkyū-buntansha) |
WATANABE Takashi Nagoya University, Eco Topia Science Institute, Professor, エコトピア科学研究所, 教授 (40182927)
INOUE Yoshihiro Gifu University, Faculty of Engineering Mechanical & Systems Eng., Associate Professor, 工学部, 助教授 (00176455)
福島 千晴 広島工業大学, 工学部, 助教授 (30262752)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Keywords | Three-dimensional turbulent flow / Rotating cylinder / Coherent structure / Boundary layer / Spiral vorted / Proper orthogonal decomposition / Intermittency factor / Spectrum / 動的組織構造 / VITA法 / 四象限分割法 |
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| Research Abstract |
The objective of the present study is to investigate experimentally the coherent structure of the turbulent boundary layer, which has skewed velocity profiles, on a rotating cylinder in an axial flow, and, in particular, to identify and clarify the spiral vortex structure in this boundary layer. This flow is one of the basic models of three-dimensional turbulent wall flows, which should be treated as the complex turbulent flows affected by body forces and extra rates of strain.
For a stationary cylinder, the bursting phenomena and the turbulent coherent structure were investigated using VITA technique and four-quadrant method from the instantaneous time-series data obtained. Any critical differences in these quantities from the flat-plate turbulent boundary layer were not found.
In order to investigate the spiral vortex structure, a measuring system utilizing hot-wire rake was constructed, and firstly an attempt was made to extract the coherent structure of the flat-plate boundary layer.
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The analysis of proper orthogonal decomposition as one of the tool to extract the coherent structure was undertaken for the multi-point instantaneous time-series data. The result showed that the eigenfunction of the second mode as well as the first mode was crucial to identify the coherent structure. The turbulent and non-turbulent character in outer region of the turbulent boundary layer that is one of the structures of the outer layer was discerned by using the first and the second modes.
Skewed mean velocity profiles and fluctuating velocity distribution in case of rotating cylinder were measured using the hot-wire anemometry, and the validity of several laws of the universal velocity distribution proposed so far with respect to the measured mean velocity profiles were examined.
An attempt was made by using the flatness factor and intermittency factor to inquire the coherent structure in the outer region, but it was difficult to capture any structure proper to the rotating cylinder with these parameters. Then the power spectra of the fluctuating velocities were investigated. Each of the power spectra for the rotating cylinder exhibited a bump in the middle frequency range, whereas for the stationary cylinder as well as for the flat plate they decreased monotonically with increase in the frequency, and the bump frequency became higher as the rotation speed increased. This fact showed clearly that the coherent structure of the turbulent boundary layer on a rotating cylinder was fairly regular enough to reveal itself in the spectrum, and it was suggested that there existed a spiral vortex structure enwinding the cylinder. Less
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