边界层燃烧在超燃冲压发动机内的摩擦减阻特性

Skin friction reduction for boundary layer combustion in a scramjet engine

以模型超燃冲压发动机为研究对象,该文设计了一种边界层燃烧装置,基于考虑边界层转捩的四方程Transition SST湍流模型,化学反应动力学模型采用9组分27步反应的氢气/氧气反应模型,对边界层燃烧在超燃冲压发动机内的摩擦减阻特性进行数值模拟研究。结果表明:引入边界层燃烧可以使超燃冲压发动机燃烧室壁面摩擦阻力得到大幅度降低。发动机下壁面采用扩张型面会抑制燃烧室内的边界层燃烧,不利于燃烧室内的壁面摩擦减阻,但尾喷管段的减阻效果更为明显;而当发动机流道下壁面向主流收缩时会增强燃烧室内的边界层燃烧,进而增大燃烧室内的减阻效果,但不利于尾喷管段的减阻,若能保持燃烧室下游的边界层燃烧火焰,采用收缩型面构型的发动机减阻效果最优。

The skin friction characteristics for boundary layer combustion in a scramjet engine were studied numerically by analyzing the effect of adding a boundary layer combustion device and for changes in the scramjet exhaust nozzle lower wall inclination angle. The combustion was modeled using a hydrogen-air kinetics model consisting of 9 species and 27 reaction steps with the flow modeled. The turbulence was modeled using the four-equation Transition SST(shear stress transport) turbulence model which takes account the boundary layer transition to accurately predict the hydrogen combustion in the boundary layer with the hydrogen injected from the boundary layer combustion device. The investigation of the effects of various exhaust nozzle lower wall inclination angles shows that the flow expansion inhibits boundary layer combustion in the combustion chamber while dramatically reducing the skin friction in the exhaust nozzle. In contrast, a contracting exhaust nozzle enhances the boundary layer combustion in the combustion chamber while increasing the flow resistance. However, the boundary layer flame is extinguished before it propagates into the nozzle section, which further increases the skin friction. Thus, if the boundary layer combustion flame can be spread into and stabilized in the nozzle section, the scramjet with a contraction profile will exhibit superior skin friction reductions.