以同轴射流燃烧器为研究对象,对6 mm、11.4 mm和17.4 mm 3种燃烧器直径下的甲烷空气同轴射流扩散火焰进行数值模拟,研究了氧气质量分数在23%~48%内扩散火焰的闪烁特性。结果表明:使火焰稳定的伴流速度比值Ur随着燃烧器直径的增大而增加,...以同轴射流燃烧器为研究对象,对6 mm、11.4 mm和17.4 mm 3种燃烧器直径下的甲烷空气同轴射流扩散火焰进行数值模拟,研究了氧气质量分数在23%~48%内扩散火焰的闪烁特性。结果表明:使火焰稳定的伴流速度比值Ur随着燃烧器直径的增大而增加,3种燃烧器直径下抑制火焰振荡所对应的Ur值分别为0.647、2.2和11.4;作用在火焰面外部的涡旋随着Ur的增大逐渐向火焰下游推移,同时峰值闪烁频率增加,而火焰的振荡幅度逐渐减小,流动与换热特性由周期性振荡转变为混沌状态;火焰的振荡幅度随着氧气质量分数的增加而减小,当氧气质量分数为48%时,火焰的闪烁峰值频率为10 Hz,且火焰闪烁的峰值频率不随氧气质量分数发生变化。展开更多
In turbulent combustion simulations, the flow structure at the unresolved scale level needs to be reasonably modeled. Following the idea of turbulent flamelet equation for the non-premixed flame case, which was derive...In turbulent combustion simulations, the flow structure at the unresolved scale level needs to be reasonably modeled. Following the idea of turbulent flamelet equation for the non-premixed flame case, which was derived based on the filtered governing equations(L. Wang, Combust. Flame 175, 259(2017)), the scalar dissipation term for tabulation can be directly computed from the resolved flowing quantities, instead of solving species transport equations. Therefore, the challenging source term closure for the scalar dissipation or any assumed probability density functions can be avoided;meanwhile the chemical sources are closed by scaling relations. The general principles are discussed in the context of large eddy simulation with case validation. The new model predictions of the bluff-body flame show sufficiently improved results, compared with these from the classic progress-variable approach.展开更多
基金the National Natural Science Foundation of China(Grant No.11572330)the support from the Engineering Research Center of Gas Turbine and Civil Aero Engine,Ministry of Education of China+1 种基金the support from International Clean Energy Talent Program by China Scholarship Council(Grant No.201904100044)Open founding of National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics of China(Grant No.6142702180307).
文摘In turbulent combustion simulations, the flow structure at the unresolved scale level needs to be reasonably modeled. Following the idea of turbulent flamelet equation for the non-premixed flame case, which was derived based on the filtered governing equations(L. Wang, Combust. Flame 175, 259(2017)), the scalar dissipation term for tabulation can be directly computed from the resolved flowing quantities, instead of solving species transport equations. Therefore, the challenging source term closure for the scalar dissipation or any assumed probability density functions can be avoided;meanwhile the chemical sources are closed by scaling relations. The general principles are discussed in the context of large eddy simulation with case validation. The new model predictions of the bluff-body flame show sufficiently improved results, compared with these from the classic progress-variable approach.
