反非平衡剪切流模拟中的意外二次流动
Unexpected secondary flows in reverse nonequilibrium shear flow simulations
AI总结：
研究发现反非平衡模拟在长流方向的模拟盒中会产生意外二次流动，揭示了该方法在复杂流体模拟中的局限性。
摘要：
我们模拟了两种粒子基流体模型，即多粒子碰撞动力学和耗散粒子动力学，在剪切作用下使用反非平衡模拟（RNES）。在立方周期性模拟盒中，牛顿流体的预期剪切流分布与流体粘度一致。然而，当模拟盒在流方向延伸时，意外的沿剪切梯度的二次流动形成。当模拟盒在剪切梯度维度上比流维度长时，标准剪切流分布被获得，而当流维度至少比剪切梯度维度大25%时，二次流动始终存在。这些二次流动满足由RNES施加的边界条件，并且在流体中比相应的单向流动具有更低的粘性耗散率。这项工作强调了RNES在生成流体在长流维度的模拟盒中的限制，这是在复杂流体如聚合物溶液中应用RNES时的重要考虑因素。
英文摘要：
We simulated two particle-based fluid models, namely multiparticle collision dynamics and dissipative particle dynamics, under shear using reverse nonequilibrium simulations (RNES). In cubic periodic simulation boxes, the expected shear flow profile for a Newtonian fluid developed, consistent with the fluid viscosities. However, unexpected secondary flows along the shear gradient formed when the simulation box was elongated in the flow direction. The standard shear flow profile was obtained when the simulation box was longer in the shear-gradient dimension than the flow dimension, while the secondary flows were always present when the flow dimension was at least 25% larger than the shear-gradient dimension. The secondary flows satisfy the boundary conditions imposed by the RNES and have a lower rate of viscous dissipation in the fluid than the corresponding unidirectional flows. This work highlights a previously unappreciated limitation of RNES for generating shear flow in simulation boxes that are elongated in the flow dimension, an important consideration when applying RNES to complex fluids like polymer solutions.
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