摘要
采用态-态模型在总温T_(0)=2000K~8000 K、总压p_(0)=1~20 MPa范围,开展高温空气准一维非平衡喷管流动数值模拟.考虑5种化学组元(N_(2),O_(2),NO,N,O),其中N_(2),O_(2),N_(O)分别有61,46,48个振动能级,将不同振动能级上的粒子视为不同组元,共157个组元.对未见公开文献给出速率系数的分子能级跃迁过程,综合振动能方程松弛时间和其他类似微观过程跃迁速率系数进行折算.计算结果表明,喷管喉道前流动接近平衡,喉道后出现非平衡,喉道下游不远处发生化学组元质量分数、较低振动能级分子数和表征振动能的振动温度的冻结,N_(2)的振动温度冻结较NO和O_(2)早,冻结值也更高;对振动能级跃迁起主导作用的微观机制是平动-振动能量交换(VT)过程,复合反应生成的分子更多位于中等振动能级;喷管非平衡和冻结区域分子能级分布偏离振动温度下的玻尔兹曼分布,高能级出现过分布;提高驻室总压能够降低喷管流动非平衡程度,推迟热化学冻结发生.
Using state-to-state model,quasi-one-dimensional nozzle flow of high-temperature nonequilibrium air is investigated numerically.The five chemical species mixture N_(2)/O_(2)/NO/N/O is considered with 61 bound vibrational levels for N_(2),46 for O_(2),and 48 for NO.Each vibrational state is regarded as a pseudo species,which leads to a total of 157 species for the air mixture.The state-specific transition rate coefficients of some processes,which have no available data,are calculated based on the relaxation time and the rate coefficients of other similar processes.The flow simulation and analysis are made for reservoir temperature from 2000 to 8000 K and pressure from 1 to 20 MPa.The nozzle flow is essentially in equilibrium before the throat,but deviates from equilibrium shortly after the throat.The mass fraction of chemical species,populations of lower energy levels,and vibrational temperatures are frozen in the downstream not far away from the throat.The vibrational temperature of N_(2) is freezing earlier and has a higher frozen value than that of NO and O_(2).The process of vibration-translation(VT)energy exchange is predominant for vibrational transition,the recombination reaction generates molecules preferably to middle vibrational levels.Throughout the nonequilibrium and frozen zone,the vibrational population distributions are far from Boltzmann distribution at vibrational temperature,and feature a large overpopulation of the high-lying vibrational levels.Increasing the reservoir pressure could reduce the nonequilibrium to a certain extent and delay the flow thermochemical freezing.
作者
王辉
曾明
段欣葵
王东方
刘伟
Wang Hui;Zeng Ming;Duan Xinkui;Wang Dongfang;Liu Wei(College of Aerospace Science and Engineering,National University of Defense Technology,Changsha 410073,China)
出处
《力学学报》
EI
CAS
CSCD
北大核心
2024年第5期1377-1394,共18页
Chinese Journal of Theoretical and Applied Mechanics
基金
国家自然科学基金资助项目(11927803)。
关键词
热化学非平衡
态-态模型
振动能级分布
喷管流动
高焓风洞
thermochemical nonequilibrium
state-to-state model
vibrational population distribution
nozzle flow
high enthalpy wind tunnel
