摘要:
为解决氢气驱动空气激波风洞中激波管内氢气与空气接触区掺混燃烧产生的污染物对有效试验时间及试验气体品质的影响问题，本文提出使用氮气隔离的运行方式，通过求解准一维热化学非平衡Navier-Stokes方程，开展了氢气驱动激波风洞典型运行状态下流场的数值模拟研究。对比了氢气直接驱动空气与使用等压氮气进行隔离的流场特性，主要包括入射激波马赫数、掺混燃烧发生发展情况、激波管内驻室区域压力、温度及组分分布等特性，获得氮气隔离方式对激波风洞流场特性的影响。结果表明：氮气隔离对激波管末端入射激波马赫数影响不大，从激波强度上对总温总压模拟能力影响并不显著，驻室气体压力曲线振荡幅值减少，压力提前达到稳定，小幅度延长有效试验时间；添加氮气隔离段有效抑制了氢气驱动空气激波风洞管内燃烧的发生，主要体现在激波管内沿程水组分分布的浓度与展宽显著减小，激波管末端驻室测点的水组分浓度显著降低，同时有效抑制了驻室温度曲线骤升即燃烧放热的现象；在50 MPa氢气驱动0.1 MPa空气典型工况下，隔离段长度考虑为低压被驱动段总长1/3，能起到很好的抑制氢氧燃烧的同时又避免过多设置氮气隔离长度造成对空气总量的损失。
Abstract:
To address the adverse effects of contaminants generated by mixing and combustion in the hydrogen-air contact region of the shock tube on both the effective test time and test gas quality in a hydrogen-driven shock tunnel, a nitrogen isolation operating mode was proposed. Numerical simulations were conducted to investigate the flow field under typical operating conditions of the shock tunnel. The quasi-one-dimensional thermochemical non-equilibrium Navier-Stokes equations were solved, where a cubic equation of state was employed to evaluate the thermodynamic properties of high-temperature gases. The wall friction and heat transfer along the tube, as well as the thermochemical non-equilibrium effects, were comprehensively considered. The flow field characteristics under two configurations, namely direct hydrogen-air contact operation and isobaric nitrogen isolation operation, were compared, covering incident shock Mach number, onset and evolution of mixing-induced combustion, as well as pressure, temperature and species distribution in the stagnation chamber of the shock tube. On this basis, the influence of the nitrogen isolation mode on the flow field characteristics of the shock tunnel was clarified. The results show that nitrogen isolation has little effect on the incident shock Mach number at the end of the shock tube, and exerts no notable impact on the tunnel’s capability to reproduce total temperature and total pressure in terms of shock strength. The oscillation amplitude of the gas pressure curve in the stagnation chamber is reduced, and the pressure stabilizes earlier, which slightly prolongs the effective test time. The addition of a nitrogen isolation section effectively suppresses combustion inside the shock tunnel. This is mainly manifested in a significant reduction in both the concentration and axial distribution width of water species along the shock tube, as well as a marked decrease in water species concentration at the monitoring point in the stagnation chamber at the end of the shock tube. Meanwhile, it effectively inhibits the sudden rise in the stagnation chamber temperature curve caused by combustion heat release. Under the typical condition of hydrogen at 50 MPa driving air at 0.1 MPa, setting the nitrogen isolation length to approximately one-third of the total length of the low-pressure driven section can achieve satisfactory suppression of hydrogen-oxygen combustion while avoiding excessive loss of available test air caused by an overly long nitrogen isolation section. Keywords: shock tunnel; shock tube; quasi-one-dimensional numerical simulation; mixing and combustion
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