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Coarse-grained simulation approach for turbulent nonequlibrium plasma flows

机译：湍流非平衡等离子体流的粗粒度模拟方法

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摘要

Non-transferred arc plasma torches are at the core of diverse applications such as plasma spray and waste treatment. Computational simulations of these torches can provide important understanding to aid equipment design and process optimization. These plasma flows are often turbulent and present significant differences in the temperature of electrons compared to that of heavy-species. The multiphysics nature of plasmas, large variation of material properties, together with their propensity to turbulent behavior, make their computational simulation exceedingly challenging. No approach is particularly established for modeling of turbulent plasmas. This research addresses the pressing need for a consistent and complete, yet computationally feasible, turbulent plasma flow model for the exploration of industrial turbulent plasma phenomena with the fidelity and predictive capabilities achieved in other disciplines. To that end, a nonlinear type of Variational Multiscale (VMS) method, denoted as VMSn is developed. In contrast to classical VMS that neglects the effect of small scales on the transport operator, VMS n addresses the inter-dependence between large- and small-scales upfront. Moreover, a novel algebraic approximation of the small-scales, suitable for generic transport problems, denoted as Transport-Equivalent Scaling (TES) is investigated. The evaluation of the TES is done through the simulation of benchmark incompressible, compressible, and magnetohydrodynamic flow problems. Results demonstrated that TES seamlessly handles different type of flows in a unified manner. Furthermore, the new VMSn approach is evaluated with benchmark two- and three-dimensional incompressible, compressible, and magnetohydrodynamic laminar flow problems, the incompressible Taylor-Green vortex flow, and the turbulent free jet. Simulation results show that VMS n leads to minor improvements in accuracy with respect to classical VMS for laminar flow problems, but to significantly greater accuracy for the turbulent incompressible flow cases. Finally, based on the successful performance of VMSn in resolving the small scales in turbulent incompressible regimes, VMSn is used for simulation of turbulent plasma flows in arc plasma torches. Results show that the nonequilibrium plasma flow simulation using VMSn reproduces the main experimentally-observed flow dynamics of the arc inside the torch together with the evolution of turbulence in the produced plasma jet in a cohesive manner. The obtained results depict that the high temperature of the jet core have a more pronounced effect on the development of turbulence than the forcing caused by the dynamics of the arc.
机译：非转移电弧等离子炬是等离子喷涂和废物处理等多种应用的核心。这些割炬的计算仿真可以提供重要的理解，以帮助设备设计和过程优化。这些等离子体流通常是湍流的，与重物种相比，它们的电子温度存在显着差异。等离子体的多物理场性质，材料特性的巨大变化以及它们对湍流行为的倾向，使得它们的计算模拟极具挑战性。尚未专门建立用于湍流等离子体建模的方法。这项研究满足了迫切需要的一种一致，完整，但在计算上可行的湍流等离子体流模型，用于探索工业湍流等离子体现象，并具有在其他学科中获得的保真度和预测能力。为此，开发了非线性类型的变分多尺度（VMS）方法，称为VMSn。与传统的VMS忽略了小规模对运输运营商的影响相比，VMS n解决了前期大规模和小规模之间的相互依赖性。此外，还研究了一种适用于一般运输问题的小规模新颖代数逼近，称为运输当量换算（TES）。 TES的评估是通过模拟基准不可压缩，可压缩和磁流体动力流动问题来完成的。结果表明，TES以统一的方式无缝处理了不同类型的流。此外，对新的VMSn方法进行了基准二维和三维不可压缩，可压缩和磁流体动力学层流问题，不可压缩的Taylor-Green涡流以及湍流​​自由射流的评估。仿真结果表明，相对于层流问题的经典VMS，VMS n的精度略有提高，但是对于湍流不可压缩的流动情况，VMS n的精度明显提高。最后，基于VMSn在解决湍流不可压缩状态下的小尺度问题上的成功表现，将VMSn用于模拟电弧等离子炬中的湍流等离子流。结果表明，使用VMSn进行的非平衡等离子流模拟再现了实验观察到的炬内部电弧的主要流动动力学以及所产生的等离子流的内聚性。所获得的结果表明，射流核心的高温对湍流发展的影响比电弧动态产生的强迫更为明显。

著录项

  • 作者

    Modir Khazeni, Seyedeh Mahnaz.;

  • 作者单位

    University of Massachusetts Lowell.;

  • 授予单位 University of Massachusetts Lowell.;
  • 学科 Mechanical engineering.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 341 p.
  • 总页数 341
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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