氢氧燃气发生器低频燃烧稳定性仿真分析

Simulation analysis of low-frequency combustion stability of a hydrogen oxygen gas generator

针对某氢氧火箭发动机燃气发生器热试车参数存在约200~230 Hz较明显脉动的现象,建立了低频燃烧稳定性仿真数学模型,来分析是否发生了燃烧时滞相关的极限循环低频不稳定燃烧。不同燃烧时滞、喷注器压降和燃烧室容积条件下的仿真结果显示:由燃烧时滞引起的低频不稳定燃烧频率显著低于试验结果,试验中低频脉动可能是受到了供应管路声学频率的扰动。进一步分析表明:决定燃烧系统稳定性的关键参数是燃烧时滞与燃气停留时间的比值,当该比值大于临界值时系统趋于不稳定,相反系统趋于稳定。基于仿真数据拟合形成了系统固有频率计算的半经验公式,系统固有频率随着燃烧时滞与燃气停留时间之和增大而降低。获取了在不同压降占比下的稳定边界,随着喷注器压降占比的增大,系统由稳定转为不稳定的燃烧时滞与燃气停留时间的临界比值越大。

In view of the obvious pressure oscillations of 200-230 Hz in the hot test of a hydrogen oxygen rocket engine gas generator,a low frequency combustion stability simulation mathematical model was established to analyze whether there is low-frequency unstable combustion phenomenon of limit cycle related to combustion delay.Simulation results under different combustion time delay,pressure drop of injector and combustion chamber volume showed that the oscillations frequency related to the combustion time delay was significantly lower than the test data.The low-frequency fluctuation in the test data may be excited by the acoustic frequency of the feed line.Further analysis showed that the key parameter to determine the stability of the system is the ratio of combustion delay to gas residence time.When the ratio was greater than a critical value,the system became unstable,otherwise the system became stable.Based on the simulation data fitting,a semi empirical formula for calculating the inherent frequency of the system was formed.The inherent frequency of the system decreased with the increase of the sum of combustion delay and gas residence time.The stable boundary of the system under different injector pressure drops was obtained.With the increase of pressure drop ratio,the critical ratio of combustion delay and gas residence time from stable to unstable became larger.