低马赫数下多凹腔燃烧室非稳态燃烧过程

作为稳定火焰的有效手段之一，凹腔构型在冲压发动机燃烧室研究中占有重要地位。在对以煤油为燃料的多凹腔燃烧室冷/热态流动特性分析的基础上，重点研究低进口马赫数条件下燃烧室点火起动初期非稳态过程。结果表明：上游凹腔内大涡结构有助于提高燃料的驻留时间，未燃混气被高速主流带入下游凹腔内继续反应，进一步提高燃烧效率；燃油喷射速度决定被卷吸进回流区的燃油质量分数的大小，进而影响燃烧效率高低；燃烧室点火起动初期出现了主流熄火、火焰逆流传播以及主流再着火等复杂现象，火焰逆流传播现象是在上游凹腔内燃料自燃与下游燃烧释热压缩来流两种机制共同作用下完成的。

Unsteady combustion process in multi-cavity combustor at low Mach number condition

As one of the most effective structures of flame stabilizer, cavity plays an important role in the research on ramjet combustors. Flow field characteristics of the kerosene-fueled multi-cavity ramjet combustor are analyzed without and with combustion in this paper. The unsteady combustion flow field in the combustor is discussed in particular at the initial stage of ignition start-up at low inlet Mach numbers. The results show that the fuel residence time is increased by the bigger vortex in the upstream cavity. The unburned fuel is blown off to the downstream cavity for a further combustion as soon as it meets the high-speed main stream, which is helpful to improve combustion efficiency. The mass of kerosene drifted into cavities is determined by fuel-jet velocity, which would have an indirect effect on the combustion efficiency. At the beginning of the ignition start-up, the phenomena of mainstream blowout, countercurrent flame propagation and mainstream reburning appeared in the unsteady numerical study. The mechanisms of the countercurrent flame propagation are both slow reaction in first cavity and the downstream heat release.