超临界碳氢燃料流动不稳定的频域分析与数值模拟

Frequency domain analysis and simulation on flow instability of hydrocarbon fuels under supercritical condition

关键词:  再生冷却  热防护  碳氢燃料  超临界流体  流动不稳定  瞬态模拟  频域分析

Key words:  Regenerative cooling  Thermal protection  Hydrocarbon fuels  Supercritical fluid  Flow instability  Transient simulation  Frequency-domain analysis

摘要:

再生冷却通道中的流动失稳是高超声速飞行器发动机热防护技术中的核心问题之一。为研究超临界碳氢燃料在冷却通道中的流动不稳定特性，基于有限体积法及流体物性近似，发展了高效的一维瞬态模拟方法；同时，基于小扰动假设，进一步提出了用于预测稳定行为的频域分析方法。通过相关实验，验证了模型的可靠性。基于时域和频域方法的综合分析，沿内特征曲线讨论了主要失稳类型，重点分析了受密度波及Ledinegg不稳定共同影响的复合不稳定性。随后，进一步分析了工作压力和入口温度对稳定特性的耦合影响，并基于N_tpc-N_spc空间划分了稳定区域。研究发现，复合不稳定、Ledinegg不稳定以及密度波不稳定，随入口温度升高而相继消失。Ledinegg不稳定及密度波不稳定的稳定边界在N_tpc-N_spc空间具有高度相似性，而复合不稳定性的区域在较高的压力下略有缩小。

Abstract:

The flow instability in the regenerative active cooling channels is one of the key issues in the thermal protection of engine in hypersonic vehicles. To investigate the flow instabilities of the supercritical hydrocarbon fuels in the cooling channels， a one-dimensional transient model for efficient simulation was established using the finite volume method and linear approximation of fluid thermal properties. In the meantime， a frequency-domain analysis method was also proposed based on the small perturbation assumption to evaluate the stability characteristics. The calculated results were validated against the available experiments and achieved good agreements. Main types of flow instabilities along the internal characteristic curve were investigated based on a combined analysis of both the time-domain and frequency-domain methods. The compound instability subject to density-wave and Ledinegg instabilities was investigated and the underlying physical mechanism was revealed. A parametric study by virtue of N_tpc-N_spc space was also carried out to identify the coupling influences of the operating pressure and inlet temperature on the stability behaviors， and to determine the stabilization map. It is found that the compound instability， as well as Ledinegg and density-wave instabilities， disappear successively with the increase in inlet temperature. The stability boundaries of Ledinegg and density-wave instabilities exhibit high similarity in N_tpc-N_spc space， and the region of the compound instability shrinks slightly at higher pressures.