| Project/Area Number |
14540385
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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 |
物理学一般
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| Research Institution | Kyoto University (2003-2004)
National Institute for Fusion Science (2002) |
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Principal Investigator |
KIDA Shigeo Kyoto University, Graduate School of Engineering, Professor, 工学研究科, 教授 (70093234)
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| Co-Investigator(Kenkyū-buntansha) |
GOTO Susumu Kyoto University, Graduate School of Engineering, Assistant Professor, 工学研究科, 助手 (40321616)
KAWAHARA Genta Kyoto University, Graduate School of Engineering, Associate Professor, 工学研究科, 助教授 (50214672)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥4,100,000 (Direct Cost: ¥4,100,000)
Fiscal Year 2004: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2002: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Keywords | Turbulent mixing / Fluid line / Fluid surface / Stretching rate / Tubular vortex / Anti-parallel vortices / 流対面 / 伸張率 |
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| Research Abstract |
For the purpose of understanding of dynamics and qualitative description of statistics of turbulent mixing the stretching characteristics of fluid lines and surfaces are investigated numerically. The results obtained are summarized as follows. First, we examined, by use of direct numerical simulation and visualization analysis, how they are deformed and at which ratio they are being stretched in homogeneous stationary turbulence. It is shown theoretically that both the length of fluid line and the area of fluid surface increase exponentially in time, and that the accurate values of the stretching rate can never be obtained by the traditional method, i.e. with passive line or surface elements, but only by solving accurately the motion of the fluid lines and surfaces as the present study. Second, it was identified with simultaneous visualization of passive lines and fluid flows the type of fluid motion which causes strong stretching of fluid lines. There exist a number of tubular vortice
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s with concentrated vorticity in turbulence. They have a tendency to approach each other in parallel with opposite direction of vorticity. Fluid lines are stretched strongly around stagnation points of hyperbolic type associated with a pair of anti-parallel vortices. Third, a careful examination of the Reynolds number dependence of stretching rate of fluid line exhibits that it does not obey the Kolmogorov similarity law (as believed before) but increases more rapidly with the Reynolds number. This may be due to the Markovian multiplicative characteristics of the stretching process, i.e. the non-uniformity of the spatial distributions of stretched fluid line, especially the degree of fold, increases with the Reynolds number. The precise value of the exponential stretching rates of passive objects in turbulence and its Reynolds dependence would be useful in determination of parameters in turbulence modeling as well as important in understanding of dynamical characteristics of turbulence itself. Less
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