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A Study on the Marked turbulent drag reduction mechanism in DNA-diluted Fluid

DNA稀释流体显着湍流减阻机理研究

基本信息

批准号：
18560156
负责人：
HORIUTI Kiyosi
金额：
$ 2.4万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18560156/
关键词：
Turbulent drag reduction Polymer-diluted fluid Constitutive stress equation Affinity DNA Affinity of polymer strand Homogeneous shear turbulence Hierarchical energy spectrum RDA

项目摘要

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

研究了DNA稀释后流体的显著减阻机理。本文采用直接数值模拟的方法，对均匀各向同性湍流和均匀剪切湍流进行了数值模拟。我们从识别负责湍流能量级联产生的涡结构开始。结果表明，拉伸螺旋涡（Lundgren 1982，LSV）是主要负责在牛顿流体中的湍流产生。阐明了LSV的发生、生长和湮灭过程。我们发现，除了两个对称模式的配置研究在以前的作品中关于涡量对齐沿着两个螺旋片和涡管的核心区域，第三个非对称模式提取。螺旋片的螺旋圈通过差动旋转的收紧产生了较小尺度的速度波动的级联。基于o ...更多信息我们推测DNA稀释液中的显著减阻是由DNA抵抗弯曲的刚度引起的，我们考虑了非亲和性对聚合物链抵抗宏观应变的响应的影响。使用Johnson-Segalman本构方程（约翰逊和Segalman 1977）来近似对聚合物应力的非仿射效应。当非仿射效应最大时，确实实现了湍流产生的最大减少。其次，我们研究了湍流中的能谱特性。对构成惯性子区基态的Kolmogorov -5/3能谱的修正产生了-7/3能谱，它是由耗散率ε的波动引起的，代表了非平衡态（Yoshizawa 1994）。我们将以ε的时间变化为条件的平均应用于能谱系综。结果表明，-7/3谱确实存在作为一个隐藏的元素的频谱。整个级联过程分为两个阶段，阶段1和2。在阶段1中，与-5/3谱的偏差，即，-7/3功率分量在低波数范围和高波数范围分别为正和负。随着-7/3次幂分量的符号的出现，包含在阶段1中的低波数范围中的能量转移到阶段2中的高波数范围。虽然-7/3谱只是短暂出现，并且当平均应用于整个能谱系综时被消除，但它作为催化剂启动级联的产生。我们进行了评估的粘弹性的影响，这一层次的频谱。结果表明，粘弹性的引入往往会抑制从相1到相2的转变的发生。随后，能量级联到更高的波数范围被减少。这种压制，在非亲和度最大的时候，也是最强的。少