燃烧室声腔结构对固体火箭发动机热声振荡影响的实验研究

Effect of acoustic cavity structure of combustion chamber on thermo-acoustic oscillation in solid rocket motor

固体火箭发动机燃烧室中的热声不稳定燃烧会对发动机的正常工作造成严重危害,为了能够对热声不稳定的影响机制有更加深刻的认识,基于缩比固体火箭发动机设计了一种平面燃烧器热声实验装置,通过开展多工况实验研究了化学当量比和燃烧室声腔结构对燃烧室中热声振荡的影响。研究发现,在长度为920 mm、内径为150 mm不含模拟药柱的燃烧室中,随着化学当量比的增加,热声振荡的幅值先增加后减小,振幅在化学当量比∅=1.31处达到最大值35.4 Pa;在含有模拟药柱的燃烧室中,随着化学当量比的变化,燃烧室中出现了热声不稳定模态转换的现象,即热声不稳定从一阶声不稳定变为二阶声不稳定。对比分析了药柱内径对两种不稳定模态频率和振幅的影响,通过测量压力衰减系数进一步分析了药柱结构特性对热声振荡的阻尼作用,发现药柱结构对热声振荡的阻尼作用随药柱内径的增大而减小。结果表明,在发动机工作过程中,随着燃面的退移,药柱的内径变大,阻尼作用会越来越小,导致发动机工作末期稳定性降低,出现燃烧不稳定现象的风险增加。

The thermo-acoustic instability combustion in the combustion chamber of solid rocket motor will cause serious damage to normal operation of the motor.In order to deeply understand the influence mechanism of thermo-acoustic instability,a plane burner thermo-acoustic experimental device was designed based on the subscale solid rocket motor.The effects of chemical equivalence ratio and chamber structure on thermo-acoustic oscillation were studied by multi-working condition tests.For the combustion chamber with 920 mm length and 150 mm inner diameter without simulated grain,the amplitude of thermo-acoustic oscillation first increases and then decreases with the increase of chemical equivalence ratio.The amplitude can reach the maximum value 35.4 Pa when∅=1.31.For the combustion chamber with simulated grain,with the change of chemical equivalence ratio,thermo-acoustic instability mode conversion phenomena appears in the combustion chamber:thermo-acoustic instability changes from first-order thermo-acoustic instability to second-order thermo-acoustic instability.The influence of grain inner diameter on the frequency and amplitude of two unstable modes was compared and analyzed.The damping effect of grain structure on thermo-acoustic oscillation was further analyzed by measuring the pressure attenuation coefficient.It is found that the damping effect of grain structure on thermo-acoustic oscillation decreases with the increase of grain inner diameter.The results show that during the working process of motor,with the regression of burning surface,the inner diameter of the grain becomes larger and the damping effect becomes smaller,resulting in the reduction stability of the motor at the end of working process,and the combustion instability is more likely to occur.