Marked Drag Reduction in Non-affine Viscoelastic Turbulence in Homogeneous Isotropic and Pipe Flows
Marked Drag Reduction in Non-affine Viscoelastic Turbulence in Homogeneous Isotropic and Pipe Flows
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均质各向同性和管流中非仿射粘弹性湍流的显着减阻
DOI：
10.1088/1742-6596/318/9/092016
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
K. Matsumoto and M. Adachi
中科院分区：
文献类型：
--
作者：
K. Horiuti;K. Matsumoto and M. Adachi
利用均匀各向同性湍流和管道流动的DNS数据，研究了聚合物稀释流中分子运动对宏观变形的非亲和性对湍流减阻的影响。通过求解非仿射Johnson-Segalman本构方程得到聚合物的应力。在这两个流中，当非亲和性为最小或最大时，DR是最大的，但当非亲和性为最大时，实现了最大的减少。作为一种极端情况，在管道流动中，平均速度分布超过了Virk的最大DR极限，并且几乎完全实现了湍流状态的再层化。在新的特征向量的基础上，得到了涡管和薄板等面的法向应力差（NSD）。结果表明，第一个NSD主要是正的，而第二个NSD沿板和管是负的。因此，一个额外的张力施加在板和管。随着有效粘度的增加，延长粘度的增加，板材和管材的抗拉伸能力增强。当非亲和性最大时，DR的主要机制是由于薄片倾向于弹回原始平面形式，因此薄片向管的转变受到限制。当非亲和最小时，产生了管，但其拉伸被管核区压力降低的湮灭所抑制。在这两种情况下，能量级联到小尺度的减少导致阻力的减少。
Effect of non-affinity of the molecular motions to the macroscopic deformation in the polymer-diluted flow on turbulent drag reduction (DR) is studied using the DNS data for homogeneous isotropic turbulence and pipe flow. The polymer stress is obtained by solving the non-affine Johnson-Segalman constitutive equation. In both flows, DR is maximal when non-affinity is either minimum or maximum, but the largest reduction is achieved when non-affinity is maximum. As an extreme case, in pipe flow, the mean velocity profile exceeds the Virk's maximum DR limit and almost complete relaminarization of turbulent state is achieved. The normal-stress difference (NSD) is obtained on the basis of new eigenvectors which span the isosurfaces of vortex tube and sheet. It is shown that the first NSD is predominantly positive, while the second NSD is negative along the sheets and tubes. Thus, an extra tension is exerted on the sheet and tube. With an increase of effective viscosity by an addition of elongation viscosity, resistance of the sheet and tube to their stretching is enhanced. The principal mechanism for DR when non-affinity is maximum is that the transformation of the sheet into the tube is restrained because the sheet tends to snap back to the original flat form. When non-affinity is minimum, the tubes are created but its stretching is suppressed by annihilation of lowering of the pressure in the tube-core region. In both cases, cascade of the energy into the small scales is diminished leading to the reduction of drag.