| Project/Area Number |
18560156
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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 | Tokyo Institute of Technology |
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Principal Investigator |
HORIUTI Kiyosi Tokyo Institute of Technology, Graduate School of Engineering, Associate Professor (10173626)
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| Co-Investigator(Kenkyū-buntansha) |
TSUJI Yoshiyuki Nagoya University, Graduate School of Engineering, Associate Professor (00252255)
MABUCHI Kunihiko University of Tokyo, Graduate School of Information Science, Technology, Professor (50192349)
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| Project Period (FY) |
2006 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥3,750,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥450,000)
Fiscal Year 2007: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
Fiscal Year 2006: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | Turbulent drag reduction / Polymer-diluted fluid / Constitutive stress equation / Affinity / DNA / Affinity of polymer strand / Homogeneous shear turbulence / Hierarchical energy spectrum / RDA |
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| Research Abstract |
We studied on the mechanism of the remarkable drag reduction in the fluid which is diluted by DNA. We dealt with the homogeneous isotropic turbulence and the homogeneous shear turbulence, and utilized the numerical data which are generated by the direct numerical simulation method. We began with the identification of the vortical structure which is responsible for generation of turbulence energy cascade. It is shown that the stretched spiral vortex (Lundgren 1982, LSV) is primarily responsible for turbulence generation in the Newtonian fluid. The genesis, growth and annihilation of LSV are elucidated. We showed that aside from the two symmetric modes of configurations studied in previous works with regard to the voracity alignment along two spiral sheets and the vortex tube in the core region, a third asymmetric mode is extracted. The tightening of the spiral turns of the spiral sheets by the differential rotation produces a cascade of velocity fluctuations to smaller scale. Based on o
… More
ur conjecture that the remarkable drag reduction in the DNA diluted fluid is caused by the stiffness of DNA against its bending, we took into account of the effect of non-affinity into the response of the polymer chain against the macroscopic straining. The non-affine effect on the polymer stress was approximated using the Johnson-Segalman constitutive equation (Johnson and Segalman 1977). The largest reduction of turbulence generation was indeed achieved when the non-affine effect was largest. Next, we investigated on the properties of the energy spectrum in turbulent flows. The corrections to the Kolmogorov -5/3 energy spectrum which constitutes a base state in the inertial subrange yields the -7/3 spectrum which is induced by the fluctuation of the dissipation rate ε and represents a nonequilibrium state (Yoshizawa 1994). We applied the averaging conditioned on the temporal variations of ε to the ensemble of the energy spectra. It is shown that the -7/3 spectrum indeed resides as a hidden element of the spectrum. The entire cascade process is divided into the two phases, Phases 1 and 2. In Phase 1, the deviations from the -5/3 spectrum, i.e., the -7/3 power component, are positive and negative in the low- and high-wavenumber ranges, respectively. The energy contained in the low-wavenumber range in Phase 1 is transferred to the high-wavenumber range in Phase 2 with the occurrence of the switchover of the sign of the -7/3 power component. Although the -7/3 spectrum appears only transiently and is eliminated when averaging is applied to the whole ensemble of the energy spectra, it acts as a catalysis to initiate the generation of the cascade. We carried out the assessment on the effect of viscoelasticity on this hierarchical spectrum. It is shown that introduction of the viscoelasticity tends to suppress the occurrence of transition from Phase 1 to Phase 2. Subsequently, the energy cascade to the higher wave-number range is reduced. This suppression was strongest when the non-affinity was largest. Less
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