Study on drag reduction mechanism with emphasis on non-affinity in polymer chain coil-stretch transition

为了揭示聚合物稀释流的减阻机理，我们进行了数值研究。聚合物链被建模为弹性哑铃。我们阐明了非亲和性在哑铃运动对DR的影响，其中它们的运动不精确地对应于宏观施加的变形。溶剂的DNS与哑铃在强制均匀各向同性湍流中的介观描述相耦合。与完全仿射情况（a=0.0）相比，当非亲和性达到最大值（a=1.0）时，实现了更剧烈的DR。当a=0.0时，哑铃接头矢量被转换为表示材料线元的逆变矢量，管状结构产生弹性。当a=1.0时，连接器作为代表材料面元的协变矢量，在平面结构上垂直向外引导，对涡片施加额外张力，导致能量级联衰减，产生较大的DR。

We carried out numerical study to reveal the mechanism of drag reduction (DR) in polymer-diluted flows. The polymer chains are modeled as elastic dumbbells. We elucidated the effect of non-affinity in the motion of dumbbells on DR, where their motions do not precisely correspond to macroscopically-imposed deformation. The DNS for the solvent is coupled to the mesoscopic description of dumbbells using BDS in forced homogeneous isotropic turbulence. Compared with the complete affine case (a=0.0), more drastic DR is achieved when non-affinity is maximum (a=1.0). When a=0.0, the dumbbell connector vector is convected as contravariant vector representing material line element and elasticity is caused on the tubular structures. When a=1.0, the connector is convected as covariant vector representing material surface element, and directs outward perpendicularly on the planar structures and exert an extra tension on vortex sheet, which leads to attenuation of energy cascade, causing larger DR.