由于微混喷嘴尺寸小、数量多且无旋流的结构特点,微混燃烧室结构可能形成新的设计准则。为探究微混喷嘴的混合特性优化方法,提取微混喷嘴内雷诺数、相对预混长度、射流动量比等特征参数,通过大涡模拟模型研究其对混合均匀性的影响规律。结果表明:微混喷嘴内预混距离增加,燃料与空气的掺混空间扩大,混合特性明显提升;在较大的射流动量比下,燃料与空气掺混更加剧烈,混合质量上升;燃料入口流速对于喷嘴混合性能的影响并不明显;雷诺数大于1×105时,喷嘴内流动达到第二自模化区,混合均匀度不再随雷诺数的变化而改变。通过特征参数对喷嘴的混合均匀度进行拟合,所得公式可在当量比为0.5~1.0、雷诺数大于1×105及入口空气温度为18~818℃时对混合均匀度进行准确预测。该公式可对微混喷嘴的混合特性进行初步计算,并为其结构设计提供参考经验。

Due to the small size, large number and non-swirl structure of the micromix nozzle, the micromix combustor structure may forma new design criterion. In order to explore the optimization method of the mixing characteristics inside the micromix nozzle, the characteristic parameters such as Reynolds number inside the nozzle, the relative premixed length and the jet momentum ratio were extracted and theeffect of the characteristic parameters on the fuel/ air mixing characteristics were studied by Large-eddy simulation model. The results showthat, with the increase of premixed distance, the mixing space is expanded, and the mixing characteristics obviously improves. Moreover,the fuel-air mixture is more intense under the large jet momentum ratio, and the mixing quality also show an upward trend. However, fuelinlet velocity has little impact on the mixing performance of the nozzle, and when the Reynolds number is above 1×105, the flow state reaches the second self-modeling region in the nozzle, and the mixing uniformity is no longer related to Reynolds number. Further, the mixing uniformity of the nozzle is fitted by these characteristic parameters, the fitting formula could accurately predict the mixing uniformitywhile the equivalence ratio is in the range of 0.5—1.0, the Reynolds number is above 1×105 and the inlet air temperature is in the rangeof 18—818 ℃ . The fitting formula can be used to preliminarily calculate the mixing characteristics of the micromix nozzle and provide reference experience for the nozzle structural design.

0 引言

1 数值模拟方法

   1.1 几何模型介绍

   1.2 模型及边界条件选取

   1.3 网格划分及无关性验证

2 数值模拟准确性验证

3 结果与讨论

   3.1 微混喷嘴内燃料与空气的混合机理

   3.2 燃料入口平均流速对混合特性的影响

   3.3 雷诺数比对混合特性的影响

   3.4 特征参数对混合特性的拟合

   3.5 不同运行工况下混合均匀度拟合公式的准确性检验

4 结论