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首页> 外文期刊>The Journal of Chemical Physics >Transient hydrodynamical behavior by dynamical nonequilibrium moleculardynamics: The formation of convective cells
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Transient hydrodynamical behavior by dynamical nonequilibrium moleculardynamics: The formation of convective cells

机译：动态非平衡分子动力学的瞬态流体动力学行为：对流细胞的形成

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摘要

We present a method based on dynamical nonequilibrium molecular dynamics (D-NEMD) thatallows one to produce rigorous ensemble averages for the transient regimes. We illustrate themethod by describing the formation of convective cells within a two-dimensional fluid system ofsoft disks in which a gravity field and a thermal gradient are present. We analyze two differentphysical settings, with the thermal gradient orthogonal or parallel to the gravity field. In bothsettings, we follow the formation of the convective flows from the initial time, when the perturbationis turned on, to the steady state. In the first setting (orthogonal fields) we investigate several differentcases, varying the initial stationary ensemble and the perturbing field. We find that the finalsteady-state convective cell is independent of the specific sequence of perturbation fields, whichonly affects the transient behavior. In all cases, we find that the convective roll is formed througha sequence of damped oscillations of the local fields (density, temperature, and velocity),superimposed to an overall relaxation toward the local steady-state values. Then, we show howD-NEMD can be applied to the Rayleigh–Bénard (RB) setting (parallel fields). In these conditions,the convective flow only establishes above a threshold, without a preferred verse of rotation. Weanalyze only the response to the ignition of the gravity field in a stationary system under the actionof a vertical thermal gradient. Also in this case we characterize the transient response by followingthe evolution of the density, temperature, and velocity fields until the steady-state RB convectivecell is formed. The observed transients are similar to those observed in the case of orthogonal fields.However, the final steady states are quite different. Finally, we briefly discuss the conditions for thegeneral applicability of the D-NEMD method
机译：我们提出了一种基于动态非平衡分子动力学（D-NEMD）的方法，该方法可以为瞬态产生严格的整体平均。我们通过描述在存在重力场和热梯度的软盘二维流体系统中对流单元的形成来说明该方法。我们分析了两种不同的物理设置，即热梯度与重力场正交或平行。在这两种情况下，我们都遵循从扰动开启的初始时间到稳态的对流的形成。在第一种设置（正交场）中，我们研究了几种不同的情况，它们改变了初始的固定合奏和扰动场。我们发现，最终稳态对流单元与扰动场的特定序列无关，这仅影响瞬态行为。在所有情况下，我们发现对流辊是通过一系列局部场的阻尼振荡（密度，温度和速度）形成的，叠加在总体上趋向局部稳态值。然后，我们展示如何将D-NEMD应用于瑞利-贝纳德（RB）设置（平行场）。在这些条件下，对流仅建立在阈值以上，而没有优选的旋转方向。我们仅分析在垂直热梯度作用下固定系统中重力场点火的响应。同样在这种情况下，我们通过跟踪密度，温度和速度场的演化来表征瞬态响应，直到形成稳态RB对流池。观察到的瞬态类似于在正交场中观察到的瞬态，但是最终稳态却大不相同。最后，我们简要讨论D-NEMD方法的一般适用条件

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