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首页> 外文学位 >Direct simulation Monte Carlo modeling of condensation in supersonic plume expansions of small polyatomic systems.
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Direct simulation Monte Carlo modeling of condensation in supersonic plume expansions of small polyatomic systems.

机译：小型多原子系统的超音速羽状膨胀中冷凝的直接模拟蒙特卡洛模型。

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摘要

The condensation phenomenon in free expansion plumes that has been observed in both space and laboratory measurements during the last several decades has a number of important aerospace applications. For example, spaceborne optical systems may be sensitive to optical contamination of their local environment by gases or condensate particles produced by the operation of attitude control system (ACS) jets. To simulate microscopic nucleation, which concerns the formation of clusters and collisions between clusters and monomers, a kinetic approach that may be applied to the direct simulation Monte Carlo (DSMC) method, is developed. The thesis research extends the previous condensation modeling performed in our research group in two important ways. First, we extend our study from the Lennard-Jones gas of argon to the study of non-Lennard Jones gases such as water. Second, we have initiated the modeling of heterogeneous condensation.;To model homogeneous condensation of small, polar molecules, such as water, accurate microscopic cluster models need to be developed. The molecular dynamics (MD) method is used to develop a model of water cluster sizes, cluster-monomer collisions, and sticking probabilities necessary for the study of water homogeneous condensation in a plume expanding to low pressure, space conditions. The MD results are integrated into DSMC simulations of homogeneous condensation in free expansion water plumes and the simulated Rayleigh scattering intensities are compared with the Arnold Engineering Development Center (AEDC) experimental data.;The simulation results show that the nucleation rate is a key factor for accurately modeling condensation phenomenon. We use MD simulations of a free expansion to explore the microscopic mechanisms of water dimer formation and develop collision models required by DSMC. The bimolecular dimer cluster formation mechanism was found to be the main mechanism in expanding flows to vacuum. MD simulations between two water molecules were performed to predict the bimolecular dimer formation probability. The probabilities and post-collisional velocity and energy distributions were then integrated into DSMC simulations of a free expansion of an orifice condensation plume with different chamber stagnation temperatures and pressures. The terminal dimer mole fraction, similar to experiment, was found to decrease with chamber stagnation temperatures and increase linearly with chamber stagnation pressures, which is consistent with a bimolecular nucleation mechanism.;A new heterogeneous condensation model, kinetic-based model of N2 molecules condensing on CO2 nuclei, was developed using MD techniques and was implemented in the DSMC simulation of an expanding heterogeneous condensation flow of a 5% CO2 and 95% N2 mixture experimentally studied at AEDC. Another nitrogen flow for the same expansion conditions was observed to not produce any clusters. It was found that incorporation of the heterogeneous condensation process of N2 molecules condensing on CO2 nuclei causes the average cluster size to increase from 10 (the homogeneous condensation result) to about 2,000. The predicted Rayleigh scattering intensity from the simulation results was found to agree well the AEDC experimental data.;In addition to the condensation studies, the thesis also includes the DSMC modeling of radiation from a side jet, a chemically reacting, three-dimensional plume-atmospheric interaction at high altitudes. Highly nonequilibrium radiation transitions from electronically excited states generated by collisions of atomic oxygen with the reaction control system thruster plumes is modeled for different altitudes and vehicle velocity conditions. The radiation rate is compared for two types of overlay methods and with direct simulation in DSMC. This research enabled the development of the SMILE software in terms of majorant collision frequency schemes, elastic/inelastic collisions and chemical reaction models. It is however outside the scope of the majority of this doctoral research and so is included as Appendix A.
机译：在过去的几十年中，在空间和实验室测量中都观察到自由膨胀羽流中的凝结现象，在航空航天领域有许多重要应用。例如，星空光学系统可能对由姿态控制系统（ACS）喷头的操作产生的气体或凝结颗粒对本地环境的光学污染敏感。为了模拟涉及团簇形成以及团簇与单体之间碰撞的微观成核作用，开发了一种可应用于直接模拟蒙特卡洛（DSMC）方法的动力学方法。本文的研究从两个重要方面扩展了我们研究小组中先前进行的凝结建模。首先，我们将研究范围从氩的伦纳德·琼斯气体扩展到诸如水之类的非伦纳德·琼斯气体的研究。其次，我们启动了非均相缩合的建模。为了模拟小的极性分子（例如水）的均相缩合，需要开发精确的微观簇模型。分子动力学（MD）方法用于建立水团簇尺寸，团簇-单体碰撞和黏附概率的模型，该模型是研究在羽流扩展到低压，空间条件下的水均匀冷凝的必要条件。将MD结果集成到DSMC自由膨胀水流中均匀凝结的DSMC模拟中，并将模拟的瑞利散射强度与Arnold工程开发中心（AEDC）实验数据进行比较。准确地模拟冷凝现象。我们使用自由扩展的MD模拟来探索水二聚体形成的微观机制，并开发DSMC所需的碰撞模型。发现双分子二聚体簇形成机理是将流膨胀至真空的主要机理。在两个水分子之间进行MD模拟以预测双分子二聚体形成的可能性。然后将概率，碰撞后速度和能量分布整合到DSMC模拟中，以不同的腔室停滞温度和压力对节流孔凝结羽流进行自由膨胀。与实验相似，发现末端二聚体摩尔分数随腔室停滞温度降低而降低，并随腔室停滞压力线性增加，这与双分子成核机理相符。利用MD技术开发了CO2核，并在DSMC模拟中对AEDC实验研究的5％CO2和95％N2混合物不断膨胀的非均相冷凝流进行了模拟。观察到在相同膨胀条件下的另一个氮气流不会产生任何簇。已经发现，N2分子在CO2原子核上冷凝的异质缩合过程的结合使平均簇尺寸从10（均相缩合结果）增加到大约2,000。从模拟结果中预测的瑞利散射强度与AEDC实验数据非常吻合。除了冷凝研究以外，本文还包括DSMC对侧喷辐射，化学反应，三维羽状流的建模。在高海拔的大气相互作用。针对不同的海拔高度和车速条件，对原子氧与反应控制系统推进器羽流碰撞产生的电子激发态的高度非平衡辐射跃迁进行了建模。比较了两种叠加方法的辐射率以及在DSMC中的直接仿真。这项研究使SMILE软件能够在主要的碰撞频率方案，弹性/非弹性碰撞和化学反应模型方面进行开发。但是，它不在本博士研究的大多数范围内，因此被列为附录A。

著录项

  • 作者

    Li, Zheng.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Engineering Aerospace.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 200 p.
  • 总页数 200
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 航空、航天技术的研究与探索;
  • 关键词

  • 入库时间 2022-08-17 11:38:27

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