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Computational Study of Nonequilibrium Chemistry in High Temperature Flows.

机译：高温流动中非平衡化学的计算研究。

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摘要

Recent experimental measurements in the reflected shock tunnel CUBRC LENS-I facility raise questions about our ability to correctly model the recombination processes in high enthalpy flows. In the carbon dioxide flow, the computed shock standoff distance over the Mars Science Laboratory (MSL) shape was less than half of the experimental result. For the oxygen flows, both pressure and heat transfer data on the double cone geometry were not correctly predicted. The objective of this work is to investigate possible reasons for these discrepancies. This process involves systematically addressing different factors that could possibly explain the differences. These factors include vibrational modeling, role of electronic states and chemistry-vibrational coupling in high enthalpy flows.;A state-specific vibrational model for CO2, CO, O2 and O system is devised by taking into account the first few vibrational states of each species. All vibrational states with energies at or below 1 eV are included in the present work. Of the three modes of vibration in CO2 , the antisymmetric mode is considered separately from the symmetric stretching mode and the doubly degenerate bending modes. The symmetric and the bending modes are grouped together since the energy transfer rates between the two modes are very large due to Fermi resonance. The symmetric and bending modes are assumed to be in equilibrium with the translational and rotational modes. The kinetic rates for the vibrational-translation energy exchange reactions, and the intermolecular and intramolecular vibrational-vibrational energy exchange reactions are based on experimental data to the maximum extent possible. Extrapolation methods are employed when necessary. This vibrational model is then coupled with an axisymmetric computational fluid dynamics code to study the expansion of CO2 in a nozzle.;The potential role of low lying electronic states is also investigated. Carbon dioxide has a single excited state just below the dissociation limit. CO and O recombine exclusively to this excited state and then relaxes to the ground electronic state. A simple model is proposed to represent the effect of this intermediate state in the recombination process. Preliminary results show that this excited electronic state is a potential reason for increased shock standoff distance observed in LENS facility.;The general role of chemistry-vibrational coupling in modeling recombination dominated flows is also investigated. A state-specific model is developed to analyze the complex chemistry-vibration coupling present in high enthalpy nozzle flows. A basic model is formulated assuming molecules are formed at a specific vibrational level and then allowed to relax through a series of vibration-vibration and vibration-translation processes. This is carried out assuming that the molecules behave as either harmonic or anharmonic oscillators. The results are compared with the standard vibration-chemistry model for high enthalpy nozzle flows. Next, a prior recombination model that accounts for the rotational-vibrational coupling is used to obtain prior recombination distribution. A distribution of recombining states is obtained as a function of the total energy available to the system. The results of this model are compared with recent experiments. Additionally, a reduced model is formulated using the concepts of the state-specific model. The results of this reduced model is compared with the state specific model.
机译：在反射式冲击隧道CUBRC LENS-I设备中进行的最新实验测量提出了有关我们正确模拟高焓流中复合过程的能力的问题。在二氧化碳流中，在火星科学实验室（MSL）形状上计算出的冲击距离距离小于实验结果的一半。对于氧气流，双锥几何形状的压力和传热数据均未正确预测。这项工作的目的是调查这些差异的可能原因。此过程涉及系统地解决可能解释差异的不同因素。这些因素包括振动建模，电子态的作用以及高焓流中的化学振动耦合。;通过考虑每个物种的前几个振动态，设计了针对CO2，CO，O2和O系统的特定于状态的振动模型。 。能量等于或低于1 eV的所有振动状态都包括在本工作中。在CO2的三种振动模式中，将反对称模式与对称拉伸模式和双简并弯曲模式分开考虑。由于费米共振，两种模式之间的能量传递速率非常大，因此对称模式和弯曲模式被分组在一起。假设对称和弯曲模式与平移和旋转模式处于平衡状态。振动-平移能量交换反应的动力学速率以及分子间和分子内的振动-振动能量交换反应均基于最大可能的实验数据。必要时采用外推法。然后，将此振动模型与轴对称计算流体动力学代码耦合，以研究喷嘴中CO2的膨胀。;还研究了低位电子态的潜在作用。二氧化碳具有仅在离解极限以下的单一激发态。 CO和O仅复合到此激发态，然后松弛到基态电子态。提出了一个简单的模型来表示这种中间状态在重组过程中的作用。初步结果表明，这种激发电子状态是在LENS装置中观察到的激进距离增加的潜在原因。;还研究了化学振动耦合在模拟复合流中的一般作用。建立了特定于状态的模型，以分析高焓喷嘴流中存在的复杂的化学-振动耦合。假设分子是在特定的振动水平下形成的，然后通过一系列振动-振动和振动平移过程使其松弛，则可以制定基本模型。假设分子表现为谐波或非谐振荡器，则可以执行此操作。将结果与用于高焓喷嘴流量的标准振动化学模型进行比较。接下来，使用考虑旋转振动耦合的先验重组模型来获得先验重组分布。获得重组状态的分布，该分布是系统可用总能量的函数。该模型的结果与最近的实验进行了比较。另外，使用状态特定模型的概念来制定简化模型。将该简化模型的结果与状态特定模型进行比较。

著录项

  • 作者

    Doraiswamy, Sriram.;

  • 作者单位

    University of Minnesota.;

  • 授予单位 University of Minnesota.;
  • 学科 Engineering Aerospace.;Physics High Temperature.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 111 p.
  • 总页数 111
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

  • 入库时间 2022-08-17 11:36:56

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