【作者】 孙虹宇；

【导师】 张文飞；

【作者基本信息】 燕山大学 ， 流体力学， 2010， 硕士

【摘要】 随着纳米科技的日益发展,迫切需要了解纳米尺度流动特性。由于实验和理论研究的困难,分子动力学模拟方法成为探索纳米尺度流动问题的有力工具。在研究流动特性过程中,如何分离出真实的流速成为众多难点之一。传统的分子动力学方法是把流速与,分子热运动速度之和在一个长时间段上取平均值,这种方法只在流速相当大的情况下适用。对于低速流动问题,由于较低的流动速度和较高的分子热运动速度的非线性耦合,流体的流速被大大地高估,失去其真实性。低速纳米尺度流动速度的求解是解决纳米尺度流动问题的基础,所以对这个问题的成功解决具有十分重要的意义。本文首先对两种纳米尺度流速求解方法进行系统的阐述和比较,然后采用流体力学中的牛顿内摩擦定律公式和分子动力学相结合的新方法,通过模拟液氩在圆截面纳米通道内的三维Poiseuile流动,研究流体的流动特性。通过改变流动模型的径向尺寸、壁面与流体之间的作用力和载荷加速度的大小,建立了多个模拟模型。模拟高速流动,将应用新方法求得的流速分布与传统的分子动力学方法得到的流速分布进行比较,观察是否具有一致性。模拟低速流动,观察得到的流速分布是否稳定。研究结果表明:在流体高速流动时,新方法求得的流速与传统的分子动力学方法求出的流速十分接近;在低速流动时,新方法也能得到稳定的流速。通过模拟研究了模型的径向尺寸、壁面与流体之间的作用力和载荷加速度对流动的影响,考察的主要信息包括流体的密度分布、粘度分布、剪切应力分布和速度分布,通过比较得到了许多重要的结论。更多还原

【Abstract】 With the development of modern science and nanotechnology, the behavior of nanoscale fluid has been attracting more and more attention. As the difficulties of experimental and theoretical studies, molecular dynamics simulations has been a powerful tool to explore nanoflow problems. In the process of studying flow characteristics, how to extract the true flow velocity is a major difficulty. The flow velocity got by traditional molecular dynamics method is the average value of bulk flow velocity and the molecules’thermal motion over time. This method only can apply in the case of high speed flow problems. For low speed flow problems, because of the highly nonlinear coupling of the low bulk flow velocity and the high velocity of molecules’thermal motion, and usually over-estimate the true flow velocity in such cases and lose its authenticity. Calculation of flow velocity in low speed nanoflow problems is the basis for nanoflow problems, so the successful resolution of this issue has great significance.In the paper, firstly, two kinds of solution method of flow velocity in nanoflow system were described and compared, and combine Newton’s law of internal friction and molecular dynamics method, Three-dimensional liquid argon Poiseuille flows in circular cross sectional nanochannels are simulated and the flow characteristics are studyed with this new method. By changing the radial size of flow model and external force and wall-fluid interaction, established a number of simulated examples. Simulation results show that: high-speed flows, the flow velocities obtained by the new method are close to conventional results, for low speed flows, the flow velocities calculated by the new method are still stable. By simulation, focused on the effect of the radial size of flow model and external force and wall-fluid interaction, We mainly pay attention to density and viscosity and shear stress and flow velocity distribution, and get a number of important conclusions by comparing.更多还原