具有气液同轴喷嘴的液体火箭发动机燃烧室压力振荡及其声学特性研究

Properties of Pressure Oscillations and Acoustic Features in Combustor of Liquid Rocket Engine with Gas-Liquid Coaxial Injectors

关键词:  液体火箭发动机  燃烧不稳定性  声学特性  气液同轴喷嘴  燃烧室

Key words:  Liquid rocket engine  Combustion instability  Acoustic feature  Gas-liquid coaxial injector  Combustion chamber

摘要:

为探究液氧/煤油液体火箭发动机气液同轴喷嘴模型燃烧室具有良好稳定性的原因，采用非稳态雷诺平均（URANS）方法数值研究了其燃烧不稳定性和声学特征。两相燃烧条件下，燃烧室压力振荡幅值约为室压的10%左右、最大不超过25%，且以纵向和横向振型为主。一周六径隔板对横向振型具有很强的抑制作用，但对纵向振型影响较小。与液-液撞击式液氧/煤油发动机模型燃烧室相比，本文研究的燃烧室中煤油液滴没有发生超临界蒸发现象，第三邓克尔数较小，诱发燃烧不稳定性的激励源较弱。进一步通过数值定容弹激发了燃烧室多模态声学特征压力振荡，并得到了其振荡特征频率、幅值和衰减率。结果表明，气喷嘴具有1/4波长喷嘴特征，能显著减小目标振型的幅值，而集气腔对纵向振型具有很强的抑制作用，同时对其他振型也有程度不同的抑制效果。因此，较弱的燃烧不稳定性激发机制以及隔板、气喷嘴和集气腔对纵向和横向振型有很强的抑制作用，使得该液氧/煤油发动机气液同轴燃烧室具有很好的稳定性。

Abstract:

In order to make out why model combustion chambers of LOX/RP-1 liquid rocket engine with gas-liquid coaxial injectors are stable， numerical investigations on their combustion instability and acoustic features are carried out based on Unsteady Reynolds-Averaged Navier-Stokes （URANS）. Under the case of real two-phase combustion， the amplitudes of pressure oscillations are about 10% of chamber pressure， and their maximum values are not more than 25%. Such pressure oscillations are characterized by longitudinal and transverse acoustic modes， and one-circumferential and six-radial baffles can suppress the transverse acoustic-mode pressure oscillation significantly， while have small effects on the longitudinal acoustic-mode pressure oscillation. Compared with model combustion chamber of LOX/RP-1 engine with liquid-liquid like-impinging injector， there is no super-critical evaporation for RP-1 droplets and the third Damk?hler numbers are smaller in present model chamber. Therefore， the stimulating sources for combustion instability are weaker. Then pressure oscillations in model chamber with multi-acoustic modes are achieved by numerical constant-volume bomb， and the eigenfrequencies， amplitudes and damping factors are obtained. Gas injector is characterized by a quarter-wave resonator， and it can reduce the amplitude of target acoustic-mode pressure oscillation significantly. Plenum chamber have a strong impression on the longitudinal acoustic-mode pressure oscillation. Meanwhile， other-mode pressure oscillations are also suppressed by plenum chamber in different degrees. In general， for weaker stimulating on combustion instability and stronger inhibition on the longitudinal and transverse acoustic-mode pressure oscillation due to baffles， gas injector and plenum chamber， the combustion chamber of LOX/RP-1 liquid rocket engine with gas-liquid coaxial injectors has a good performance on stable combustion.