不同润湿性纳米通道内库埃特流动的模拟

利用非平衡分子动力学模拟方法, 模拟了两无限大平行平板组成的纳米通道内的库埃特流动, 并给出了壁面润湿性和速度对流场密度、速度分布及壁面滑移的影响规律.数值模拟中, 统计系综采用微正则系综, 势能函数选用LJ/126模型, 壁面设为刚性原子壁面, 温度校正使用速度定标法, 牛顿运动方程的求解则采用文莱特算法.结果表明, 纳米通道内流体密度呈对称的衰减振荡分布, 且随壁面润湿性的降低, 振荡幅度减小, 振荡周期保持不变;滑移量随壁面润湿性的提高而降低, 甚至在亲水壁面时出现负滑移现象;随壁面速度的增加滑移速度逐渐增大, 且在流体呈现非线性流动阶段其增幅显著加大.另外, 还发现当壁面设置为超疏水性时, 壁面滑移呈现出随润湿性降低而减小的反常现象, 并基于杨氏方程对其进行了解释.

SIMULATION OF THE LIQUID COUETTE FLOW IN A NANO-CHANNEL WITH DIFFERENT WETTABILITY

The relation between characteristics of solid surfaces and properties of destiny, velocity and slip in a nanochannel with different wettabilities is explored, using molecular dynamics simulation (MDS). In these simulations, the liquid Couette flow confined between two infinite parallel planar walls is considered, and statistical ensemble is set as NVT, and the interaction between atoms is calculated using Lennard-Jones potential energy function. The hydrophobic wall which is set to rigid surface is characterized by the low solid-liquid relative energy parameter. For all simulations, velocity-rescale method is used to keep the temperature constant and the Verlet algorithm is used to solve the Newton equations. Some conclusions are presented from the simulation results in this paper. Firstly, fluid density profiles which are adjacent to solid surfaces oscillate around the value of major fluid density, and the extents of oscillation decay, the periods of oscillation remain unchanged with the hydrophobicity increase of the solid surface. Secondly, greater hydrophobic walls lead to larger slip velocity, and the hydrophilic surface even leads to negative slip. Thirdly, slip velocity increases with the accretion of velocity of the solid surface in Couette flow, and accretion of slip velocity is accelerated greatly when the flow is in layer regime. Besides, we also find the superhydrophobic walls generate smaller slippage than hydrophobic walls, which varies from the common conception, and we explain this result basing Young's equation.