De Subhranil
Department of Physics, Indiana University Southeast, New Albany, Indiana 47150, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Nov;88(5):052311. doi: 10.1103/PhysRevE.88.052311. Epub 2013 Nov 20.
The "constitutive equation"-free scale-bridging method connecting nonequilibrium molecular dynamics and continuum fluid mechanics, that had hitherto been applied only to a parallel-plates geometry, is extended to study the flow of a polymer melt in a cylindrical pipe subject to a velocity in the direction parallel to the cylinder's axis. The system, initially at rest, is given a velocity at the cylinder's surface, and the evolution of the velocity profile within the fluid is studied, along with the time taken for the velocity to propagate toward the cylinder's axis. The said time of propagation is found to increase with the boundary velocity-a fact in contrast with the case of a Newtonian fluid for which the time of propagation is expected to be independent of the boundary velocity. For a fixed value of the boundary velocity, the propagation time is found to increase with the cylinder radius according to a power law with an exponent that is smaller than the corresponding exponent for a Newtonian fluid. For the lower values of the boundary velocity and the lower values of the radius studied, a velocity overshoot is observed at the cylinder's axis-a manifestation of elastic behavior of the fluid.
一种无“本构方程”的尺度桥接方法，此前仅应用于平行板几何形状，现在被扩展用于研究聚合物熔体在圆柱形管道中的流动，该管道受到平行于圆柱轴线方向的速度作用。系统最初处于静止状态，在圆柱表面给定一个速度，研究流体内部速度分布的演变，以及速度向圆柱轴线传播所需的时间。发现所述传播时间随边界速度增加，这一事实与牛顿流体的情况相反，对于牛顿流体，传播时间预计与边界速度无关。对于固定的边界速度值，发现传播时间随圆柱半径按照幂律增加，其指数小于牛顿流体的相应指数。对于所研究的较低边界速度值和较小半径值，在圆柱轴线上观察到速度过冲——这是流体弹性行为的一种表现。
