Recent interest in hypersonic transitional flows, transitional referring to the flow regime between continuum and free-molecular flows, is motivated by the current and projected flight activities at high altitudes and at high speeds. Simulation of such flows involves consideration of the thermochemical nonequilibrium processes in the continuum Navier-Stokes formulation. There is considerable uncertainty whether the Navier-Stokes formulation adequately describes the underlying physics. Uncertainties particularly arise in the constitutive relations and the boundary conditions at solid walls. The constitutive relations are the Navier-Stokes diffusion of momentum, Fourier's law of heat conduction, and Fick's law of diffusion of mass. The conventional boundary conditions at the solid wall are the so-called no-slip conditions for velocity and temperature.; These uncertainties led some researchers to take a completely different point of view, that is, to simulate flows directly using Monte Carlo methods in conjunction with the molecular theory of gases. However, Monte Carlo simulation methods have the disadvantage of being computationally intensive and not being efficient except for very rarefied flows. Therefore, it would be of practical and theoretical importance to resolve the above uncertainties and to extend the range of the Navier-Stokes equations to high speed low density flows with thermochemical nonequilibrium.; In this dissertation, a new thermochemical nonequilibrium formulation appropriate to hypersonic transitional flows of air has been developed. The present nonequilibrium gas model for air consists of five chemical species: diatomic species; molecular nitrogen {dollar}Nsb2{dollar}, molecular oxygen {dollar}Osb2{dollar}, nitric oxide {dollar}NO{dollar}, and atomic species; atomic nitrogen {dollar}N{dollar} and atomic oxygen {dollar}O{dollar}. The local thermodynamic state of the gas is described by three temperatures corresponding to three internal energy modes, i.e., translational temperature {dollar}T{dollar}, vibrational temperature {dollar}Tsb{lcub}v{rcub}{dollar}, and rotational temperature {dollar}Tsb{lcub}r{rcub}{dollar}. The thermal and chemical nonequilibrium processes are vibrational and rotational relaxation for the diatomic species and chemical reactions among the five chemical species. Slip and catalytic wall boundary conditions are included in the formulation. The governing partial differential equations with the proper boundary conditions are solved numerically using an implicit time marching finite volume technique.; The computed results are compared with the existing Monte Carlo simulations in terms of surface quantities such as drag and heat transfer and in terms of nonequilibrium flow structure. These extensive comparisons are used (1) to determine when and to what degree the continuum Navier-Stokes description coupled with thermochemical nonequilibrium processes is accurate for high speed low density flows; (2) to explore the idea that the continuum Navier-Stokes equations with the proper slip boundary conditions will be adequate for an extended range of low density hypersonic flow problems.
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机译：最近对高超声速过渡流的兴趣是过渡性的，指的是连续流和自由分子流之间的流态，这是由目前和预计的高海拔和高速飞行活动激发的。此类流动的模拟涉及在连续Navier-Stokes公式中考虑热化学非平衡过程。 Navier-Stokes公式是否充分描述了基础物理学存在很大的不确定性。实体壁的本构关系和边界条件尤其不确定。本构关系是动量的Navier-Stokes扩散，热传导的傅立叶定律和质量扩散的Fick定律。实心壁的常规边界条件是速度和温度的所谓防滑条件。这些不确定性导致一些研究人员采取了完全不同的观点，即直接使用蒙特卡洛方法结合气体分子理论来模拟流动。但是，蒙特卡洛模拟方法的缺点是计算量大，并且除了非常稀少的流程外效率不高。因此，解决上述不确定性并将Navier-Stokes方程的范围扩展至具有热化学非平衡作用的高速低密度流动具有实际和理论意义。本文开发了一种适用于高超声速过渡气流的新型热化学非平衡配方。当前的空气非平衡气体模型由五个化学物种组成：双原子物种；分子氮{美元} Nsb2 {美元}，分子氧{美元} Osb2 {美元}，一氧化氮{美元} NO {美元}和原子种类；原子氮{dol} N {dol}和原子氧{dol} O {dol}。气体的局部热力学状态由对应于三个内部能量模式的三个温度描述，即平移温度{T}，{振动} Tsb {lcub} v {rcub} {dollar}和旋转温度。温度{dolal} Tsb {lcub} r {rcub} {dollar}。热和化学非平衡过程是双原子物种的振动和旋转弛豫以及五个化学物种之间的化学反应。配方中包括滑移和催化壁边界条件。使用隐式时间行进有限体积技术对具有适当边界条件的支配偏微分方程进行数值求解。将计算结果与现有的蒙特卡洛模拟进行比较，包括表面量（例如阻力和热传递）和非平衡流动结构。这些广泛的比较用于（1）确定什么时候以及在多大程度上连续Navier-Stokes描述结合热化学非平衡过程对于高速低密度流是准确的； （2）探索具有适当滑移边界条件的连续Navier-Stokes方程对于扩展范围的低密度高超音速流问题是足够的。
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