超声速燃烧室中壁面凹腔结构的稳焰机理

针对凹腔稳焰机理,分别在冷态喷流和燃烧工况下探讨了改变凹腔长深比和深度对超声速流场中的燃料掺混效果及燃烧效率的影响.研究表明:增大凹腔长深比能使燃料更容易卷入凹腔,延长其在低速回流区内的掺混时间,增强掺混、提高燃烧效率;但过大的长深比对燃烧效率改善的影响消失,反而会使剪切层运动距离增大,导致凹腔后壁面再附激波增强,引起激波耗散产生的总压损失增大,使凹腔前、后壁面压差阻力增加,所以工程中建议采用长深比为5左右的凹腔结构.增大凹腔深度虽然会使激波损失增加,但能提高主流和凹腔的质量交换率,并使凹腔容积增大,能够显著提高燃料在低速回流区的掺混和火焰稳定效果,提高燃烧效率. 

Flame-holding mechanism of cavity structure in super-sonic combustor

The influences of length to depth ratio of cavity as well as its depth on the mixing effect of fuel and air and the combustion efficiency in supersonic flow field with/without reactions were numerically investigated. It is found that although increasing length to depth ratio could bring about fuel entrainment into cavity, delay the mixing time in low speed high-temperature recirculation zone and enhance the mixing and combustion efficiency. Yet, excessive length to depth ratio no longer improves combustion, but enhances the attached shock, increasing total pressure loss and drag between front and back walls. Increasing depth of cavity produces more loss of available energy induced by shock wave, but increases mass exchange rate between mainstream and cavity, enlarging cavity volume remarkably and increasing combustion efficiency.