CAS OpenIR
高超声速稀薄流动的硬球-拟颗粒模拟
赵祺
Subtype硕士
Thesis Advisor葛蔚
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword硬球-拟颗粒模拟(hs-ppm),高超声速流动,稀薄气体,圆球绕流,能量模型
Abstract

高超声速流动因其独特的物理化学特征,难以采用传统实验方法或连续介质模拟方法全面研究。本论文通过改进硬球-拟颗粒模拟(HS-PPM),显著降低了离散模拟的计算量、提高了计算效率,从而改进了该方法模拟高超声速流动的适用性。HS-PPM原本是针对气固多相流动提出的一种离散模拟方法,已成功应用于纳微尺度气体流动-扩散耦合过程的模拟。本论文为探索其在高超声速流动领域的适用性,首先分析了高超声速飞行器再入过程的流动特征,并调研了国内外在该领域的研究进展。在调研基础上,改进了HS-PPM中的壁面描述、气体表面作用模型、边界条件设置等,使其更适合描述高速流动。在此基础上论文对比了硬球模型(HS)、HS-PPM和直接模拟蒙特卡洛(DSMC)方法模拟同一高超声速圆球绕流问题的结果,表明HS-PPM的结果较DSMC更接近HS。对雷诺数为100、马赫数从4到19的三维圆球绕流,在HS-PPM中分别采用完全热边界和完全滑移边界得到了阻力系数的上下限,并与相应的HS结果吻合。上述研究表明了HS-PPM处理高超声速稀薄气体流动的可行性。通过外推填充率趋于0的圆球绕流结果、模拟马赫数为24而努森数从0.11到4.55的零攻角三维尖锥绕流及马赫数为20而努森数为0.03的长尾钝锥绕流等实例,分析其误差并指出了HS-PPM改进的方向。作为初步的误差修正,对HS-PPM引入了Larsen-Borgnakke能量模型。模拟的粒子具有平动能和包括转动、振动的内能,并根据平衡分布赋予粒子能量初值。在每次碰撞中通过随机取样更新粒子能量使碰撞后粒子不同能量模式的宏观统计值符合各自的平衡分布。对长尾钝锥的对比模拟证明能量模型的引入基本修正了无反应HS-PPM结果中激波温度偏高的问题。但对Apollo返回舱模型以马赫数33再入努森数约为0.081的大气层的模拟表明,当真实气体效应显著时仅考虑能量转化不足以修正温度误差。本论文继而提出了简单的氮氧离解反应模型,将其中的能量引入Larsen-Borgnakke能量模型并初步实现了粒子分裂模型及其算法,从而显著改进了Apollo返回舱模型算例中HS-PPM的温度场分布。本论文的研究表明并改进了HS-PPM对高超声速稀薄流动的适用性。但本论文的反应模型只考虑了比较简单的空气组分和反应网络,未来的研究还应从复杂反应模型、可变碰撞截面等多方面继续改进HS-PPM。;Hypersonic flow is difficult to be comprehensively studied by traditional experimental methods or simulation methods based on continuum hypothesis because of its unique physical and chemical characteristics. In this paper, the hard-sphere/pseudo-particle modeling (HS-PPM) is improved to overcome the shortcomings of discrete simulation including large computational load and low computational efficiency to some extent, which makes HS-PPM more feasible for studying hypersonic flow.HS-PPM was originally a discrete simulation method for microscale gas-solid multiphase flow. It has been applied successfully to flow-diffusion coupled simulation at micro- and nano-scales. In order to explore its applicability in the field of hypersonic flow, this paper first analyses the flow characteristics of reentrying hypersonic vehicles, and investigates the research progress in this field. On this basis, wall description, gas-surface interaction and boundary condition settings in HS-PPM are improved to make it more suitable for describing hypersonic flow.The results of HS simulation, HS-PPM and DSMC on the same hypersonic flow past a sphere are then compared. It shows that the results of HS is closer to HS-PPM than to DSMC. The flow past a three-dimensional sphere, with a Reynolds number of 100 and Mach numbers from 4 to 19, is simulated. In HS-PPM, the upper and lower limits of the drag coefficient are obtained by using the complete thermal boundary and the complete slip boundary respectively. The corresponding HS results are in good agreement with those obtained in HS-PPM. The work above demonstrates that HS-PPM is effective for hypersonic rarefied gas flow. By extrapolating the results of flow past a sphere to zero solid volume fraction, simulating the flow past a three-dimensional sharp cone with a Mach number of 24 and Knudsen numbers from 0.11 to 4.55, and the flow past a long tail blunt cone with a Mach number of 20 and a Knudsen number of 0.03, the directions to improve HS-PPM for hypersonic rarefied gas flow are suggested.As a preliminary attempt in these directions, the Larsen-Borgnakke energy model is introduced to HS-PPM. The simulated particles have not only kinetic energy, but also internal energy including rotational and vibrational energies. The initial values of these energies of a particle are derived from the equilibrium distribution, and updated by sampling after each collision to satisfy their equilibrium distributions statistically. The comparative simulation of a long tail blunt cone proves that the introduction of energy model basically corrects the shock temperature obtained in the HS-PPM simulation of hypersonic flow without reaction. However, the simulation of the re-entry of Apollo capsule model into the atmosphere with a Mach number of 33 and a Knudsen number of 0.081 shows that it is still insufficient when the real gas effect is significant, and reaction models should also be introduced.For this purpose, a simple nitrogen-oxygen dissociation reaction model is proposed and intergrated into the Larsen-Borgnakke energy model. The particle dissociation model and its simulation algorithm are also realized to obtain again the temperature distribution in the Apollo case simulated, with significant improvement.The researches in this paper have demonstrated and improved the applicability of HS-PPM to hypersonic rarefied flow. However, in this paper, only simple air components and reaction networks are considered in the reaction model. Future researches should continue to improve HS-PPM with complex reaction model, variable collision cross section and in other aspects. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40622
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
赵祺. 高超声速稀薄流动的硬球-拟颗粒模拟[D]. 中国科学院大学,2019.
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