【作者】 苏凌宇；

【导师】 刘卫东；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2009， 博士

【摘要】 本文基于推进剂液滴蒸发过程对压力振荡的动态响应特性可能是液体火箭发动机低频不稳定燃烧的主要激励因素,对液体火箭发动机的低频不稳定燃烧进行了数值仿真、理论分析和试验研究。主要研究内容及结果如下:(1)应用分子动力学模拟方法,从微观层次上对蒸发过程进行了数值模拟,重点研究了蒸发相变过程与气液界面特性对环境压力变化的动态响应特性。研究首次发现,气液界面厚度随环境压力和温度增大而增大,在环境压力快速下降的过程中,气化速率会明显增大。(2)建立了动态压力环境下的液滴蒸发试验台,开展了液滴蒸发速率对低频压力振荡动态响应特性的试验研究。试验结果表明,液滴蒸发速率对低频压力振荡具有快速响应能力,产生与压力振荡频率相同的振荡,但是蒸发速率的变化与环境压力的变化相位不同,蒸发速率的最大值出现在压力下降过程的后半阶段。(3)提出了饱和蒸气边界层的概念,建立了低频压力振荡环境下静止液滴蒸发的准稳态模型;提出了折算饱和蒸气边界层的概念,建立了低频压力振荡环境下运动液滴的准稳态蒸发模型。通过求解模型方程,系统地研究了液滴蒸发过程对压力振荡的动态响应特性。计算结果显示,压力振荡的幅值和频率、平均压力、环境温度以及液滴运动速度对蒸发速率的动态响应特性有很大影响。(4)提出了基于液滴蒸发过程的混合-化学反应不变时滞理论,建立了空气加热器工作过程的系统动力学模型。对空气/氧气/酒精三组元燃烧空气加热器的低频不稳定燃烧进行了数值仿真研究,系统地考察了推进剂质量混合比、酒精喷注压降、氧气和酒精供应系统对低频不稳定燃烧的影响。研究结果表明,蒸发速率对压力振荡的动态响应特性是激励低频燃烧振荡的主要因素。(5)对空气/氧气/酒精三组元空气加热器的低频不稳定燃烧进行了大量试验研究,考察了推进剂质量混合比、酒精喷注压降、氧气和酒精供应系统对低频不稳定燃烧的影响,并提出了低频不稳定燃烧的抑制措施,试验结果验证了本文提出的液滴蒸发过程对压力振荡响应特性是低频不稳定燃烧的主要激励因素这一结论的合理性。更多还原

【Abstract】 In the present thesis, the low-frequency combustion instability in liquid rocket engine is investigated with numerical simulations,theoretical analyses and experimental studies. The dynamic response characteristics of droplet evaporation to pressure oscillation are considered as the key exciting factor for low-frequency combustion instability. The main research contents and results are outlined as follows:(1) Evaporation process is simulated at micro-level with molecular dynamics simulation. The study is focused on the dynamic response of evaporation process and gas-liquid interface to pressure variation. The studies show that the thickness of gas-liquid interface is directly proportional to ambient pressure and temperature, and the evaporation rate increases clearly with the rapid drop of ambient pressure.(2) A test-facility is constructed for studying the dynamic response characteristics of droplet evaporation to low-frequency pressure oscillation. The results indicate that droplet evaporation rate can respond rapidly to low-frequency pressure oscillation, and owns the same frequency but different phase of pressure oscillation, and the maximum value of droplet evaporation rate appears in the latter period of pressure decline.(3) The concepts of saturation vapor boundary layer and converted saturation vapor boundary layer are put forward, and the quasi-steady model of droplet evaporation is established respectively under static and convection environment with the low-frequency pressure oscillation. By solving the model equations, a systematic study of the dynamic response characteristics of the droplet evaporation process to pressure oscillation is carried out. The results show that the amplitude, frequency, average pressure of pressure oscillation, ambient temperature and droplet velocity have significant impacts on the dynamic response characteristics of droplet evaporation rate.(4) Based on the time lag of combustion and droplet evapreationis, the dynamics model is established for a rocket-based air heater system. The numerical simulations are performed for the low-frequency combustion instablilities of the air/oxygen/alcohol tripropellant air heater. The effects of propellant mixture ratio, injection pressure drop, and the propellent supply pipe system on the low-frequency combustion instability are studied. The results show that the dynamic response characteristic of droplet evaporation to pressure oscillation is a major factor to inspire combustion instability.(5) Experiments are performed to study the low-frequency combustion instability in the air/oxygen/alcohol tripropellant air heater. The effects of propellant mixture ratio, injection pressure drop and the dynamic characteristics of the supply pipe system on the low-frequency combustion instability are studied, and the results of experiment prove that the dynamc response characteristic of droplet evaporation rate to pressure oscillation is the major exciting facor of low-requency combustion instability.更多还原