燃烧室机匣烧穿后的超声速射流火焰数值模拟研究

Numerical modeling study on supersonic jet flame after aero-engine combustor burn-through

依据适航条款CCAR33.17(a)和CCAR25.903(d)(1)的要求,民用航空发动机燃烧室在设计中必须考虑燃烧室内失效可能导致机匣烧穿的危害性后果,并采取相应的防火措施。在民用航空发动机设计中需要充分分析可能引发燃烧室机匣烧穿的失效模式以及烧穿后的危害性。由于燃烧室机匣内的压力较大且烧穿孔较小,其烧穿后会导致超音速射流火。开展该超音速射流火的流动及燃烧特征研究,将有利于指导发动机的防火设计。采用数值模拟方法,计算了不同压比、不同机匣烧穿孔径条件下的超音速射流火的流动与燃烧特征,分析了影响射流火速度及温度的主要参数,并与FAA的燃烧室机匣烧穿试验以及理论模型进行了比较分析。结果表明本文采用的数值模拟方法能够较好地预测该超音速射流火的火焰特征,为发动机的防火设计及后续的适航符合性验证提供支撑。

According to airworthiness standard CCAR33.17(a)and CCAR25.903(d)(1),the fire protection design of civil areo-engine combustor must be carefully considered so as to minimize the hazards to the airplane after the accident of combustor case burn-through.Therefore,in the process of engine fire protection design,the failure modes and hazards of combustor case burn-through should be fully evaluated.Based on the high pressure in the combustor and the geometry of the burn-through hole,it can be expected that the resulting jet will be an under-expanded sonic or supersonic jet.A thorough understanding of the phenomenology and processes involved in high-speed jet is essential for the proper fire protection design.In this paper,the characteristics and severity of a jet engine burn-through flame with different pressure ratios and different hole sizes were calculated by CFD modeling.Based on the modeling results,the temperature and velocity of the flame were compared with FAA combustor burn through experiments and theoretical model,which were impacted by hole size and pressure ratio.As a result,the simulation reproduced the main physical processes of burn-through flame,and a good agreement on flame Mach number and temperature was obtained.The CFD modeling method adopted in this paper is applicable in fire protection design and helpful for safety analysis of compliance demonstration for airworthiness regulation.