喷嘴内湍流运动对火焰浮起长度影响的数值模拟

为考虑喷嘴内部湍流运动对燃油雾化和火焰浮起长度的影响,将喷嘴内部的湍流流动以权重的形式加入初次破碎模型中,并对二次破碎模型进行了修正。建立了完整的燃油雾化和燃烧的数学模型。通过与实验数据对比来验证燃油雾化模型的准确性,并讨论了喷嘴内湍流运动对燃油雾化过程的影响。结果表明,湍流运动会加快液滴破碎和蒸发的速率,从而减小燃油蒸气贯穿距。火焰浮起长度的计算采用本文建立的燃油雾化模型,成功计算了火焰浮起长度随氧气体积分数、气体密度、气体温度和入射压力变化的规律。同时发现在不同气体密度和氧气体积分数的工况下,喷嘴内部湍流运动对火焰浮起长度的影响基本保持不变,分别为9%和13%；入射压力和气体温度的升高会导致喷嘴内部湍流对火焰浮起长度的影响逐渐变大。 

Numerical simulation of effect of turbulence flow in nozzle on flame lift-off length

In order to consider the effect of turbulence inside the nozzle on fuel spray and flame lift-off length, the turbulence was characterized by the length scale and time scale and added into primary breakup model in the form of weight coefficient, and the secondary breakup process was modified. A mathematical model of fuel spray and combustion was established. The mathematical model was validated by experimental data, and the effect of turbulence term on fuel spray was analyzed. Results indicated that the turbulence term can accelerate the rate of droplet breakup and evaporation, decrease the fuel vapor penetration. The calculation of the flame lift length was based on the fuel atomization model. These models can well predict the flame lift-off length at different conditions of oxygen volume fraction, ambient density, ambient temperature and injection pressure. It also can be found that the effect of turbulence inside the nozzle on flame lift-off length was 9% and 13% at different ambient density and oxygen volume fraction conditions, and the injection pressure and ambient temperature could enhance the influence of turbulence inside nozzle on flame lift-off length.