Modifications to Axially Symmetric Simulations Using New DSMC (2007) Algorithms
Modifications to Axially Symmetric Simulations Using New DSMC (2007) Algorithms
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DOI：
10.1063/1.3076481
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发表时间：
2008-07
期刊：
影响因子：
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通讯作者：
D. Liechty
中科院分区：
文献类型：
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作者：
D. Liechty
在Bird(2007)提出的DSMC(2007)算法的基础上，针对轴对称问题提出了几种改进的方法，以提高物理精度。最初是为了解决非平衡稀薄流动而发展起来的，现在通常被用来解决很大范围内的克努森数范围内的复杂问题。这些新算法包括以下功能：排除以前的冲突伙伴的最近邻冲突、分离的冲突和采样单元、自动自适应可变时间步长、修改的冲突无时间计数器程序以及不连续和事件驱动的物理过程。轴对称的解需要对模拟分子进行径向加权，因为由于单元体积的不同，靠近轴的分子代表的真实分子比远离轴的分子少。在目前的方法中，这些径向加权因子是连续的线性函数，随着每个模拟分子的径向位置而变化。结果表明，试探性碰撞次数的定义对轴线附近的平均碰撞时间有很大影响。网格处理轴对称问题的方法在轴附近也起着重要作用，特别是对于标量压力。提出了一种处理分子如何通过网格追踪的新方法，以缓解靠近表面的轴处标量压力的下降。此外，还提出了对复制缓冲器的修改，以改变复制的分子速度，同时保持分子动能和问题的轴对称性质。
Several modifications aimed at improving physical accuracy are proposed for solving axially symmetric problems building on the DSMC (2007) algorithms introduced by Bird. Originally developed to solve nonequilibrium, rarefied flows, the DSMC method is now regularly used to solve complex problems over a wide range of Knudsen numbers. These new algorithms include features such as nearest neighbor collisions excluding the previous collision partners, separate collision and sampling cells, automatically adaptive variable time steps, a modified no-time counter procedure for collisions, and discontinuous and event-driven physical processes. Axially symmetric solutions require radial weighting for the simulated molecules since the molecules near the axis represent fewer real molecules than those farther away from the axis due to the difference in volume of the cells. In the present methodology, these radial weighting factors are continuous, linear functions that vary with the radial position of each simulated molecule. It is shown that how one defines the number of tentative collisions greatly influences the mean collision time near the axis. The method by which the grid is treated for axially symmetric problems also plays an important role near the axis, especially for scalar pressure. A new method to treat how the molecules are traced through the grid is proposed to alleviate the decrease in scalar pressure at the axis near the surface. Also, a modification to the duplication buffer is proposed to vary the duplicated molecular velocities while retaining the molecular kinetic energy and axially symmetric nature of the problem.