We study the radial distribution of pressure, density, temperature and flow velocity fields at different times in a two dimensional hard sphere gas that is initially at rest and disturbed by injecting kinetic energy in a localized region through large scale event driven molecular dynamics simulations. For large times, the growth of these distributions are scale invariant. The hydrodynamic description of the problem, obtained from the continuity equations for the three conserved quantities—mass, momentum, and energy—is identical to those used to describe the hydrodynamic regime of a blast wave propagating through a medium at rest, following an intense explosion, a classic problem in gas dynamics. Earlier work showed that the results from simulations matched well with the predictions from hydrodynamics in two dimensions, but did not match well in three dimensions. To resolve this contradiction, we perform large scale simulations in two dimensions, and show that like in three dimensions, hydrodynamics does not describe the simulation data well. To account for this discrepancy, we check in our simulations the different assumptions of the hydrodynamic approach like local equilibrium, existence of an equation of state, neglect of heat conduction and viscosity.

我们通过大规模事件驱动的分子动力学模拟，研究了二维硬球气体在不同时间的径向分布，该气体最初处于静止状态，并通过在局部区域注入动能而受到干扰。在很大程度上，这些分布的增长是尺度不变的。从三个守恒量（质量、动量和能量）的连续性方程中获得的问题的流体动力学描述与用于描述在剧烈爆炸后通过静止介质传播的冲击波的流体动力学状态的描述相同，气体动力学中的经典问题。早期的工作表明，模拟结果与二维流体动力学的预测非常吻合，但在三个维度上并没有很好地匹配。为了解决这个矛盾，我们在二维上进行了大规模的模拟，结果表明，与三维一样，流体动力学并不能很好地描述模拟数据。为了解决这种差异，我们在模拟中检查了流体动力学方法的不同假设，如局部平衡、状态方程的存在、忽略热传导和粘度。