不同飞行工况下双模态发动机流动及燃烧特性

为研究煤油燃料矩形截面双模态超燃冲压发动机在不同飞行工况下的流动及燃烧特征，在通过直连式试验验证计算方法的准确性后，对6个不同马赫数及当量比工况进行了三维定常数值模拟，得出了发动机壁面压力、一维质量平均马赫数沿流向的分布规律，分析了各工况下流场中波系结构、释热变化率等特征。研究结果表明:不同工况下发动机明显工作于两类不同的燃烧模态。当发动机处于预燃激波串前传至注油位以前的亚燃模态时，凹槽段波系相对较弱；随着激波串的前移，隔离段中形成明显的分离旋涡结构将燃料卷至上游，部分燃烧在注油位之前已完成；在燃烧室内，分离主要发生于凹槽内部，燃烧释热集中于第一凹槽头部。当发动机处于激波串未前传的超燃模态时，凹槽段波系相对更强，流动参数波动更大，燃烧在注油位以后进行，燃烧室内分离旋涡在流向跨度大，形成从第一凹槽前缘至第二凹槽处的连续流动分离；分离旋涡有助于燃烧向下游传播，因此释热沿流向分布更均匀、更分散。在过渡段诱导流动分离，促使燃烧室内形成大流向跨度的分离旋涡可能有助于燃烧向下游传播，实现分布式释热，避免释热过于集中导致激波串前传。

Flow and combustion characteristics of dual-mode scramjet under different flight conditions

In order to study the flow and combustion characteristics of kerosene fueled rectangular dual-mode scramjet under different flight conditions, the accuracy of the numerical method was verified by direct connect experiment. Three-dimensional steady numerical simulations were carried out for six cases with different equivalence ratio and Mach numbers. The distribution of the wall pressure and the one-dimensional mass average Mach number along the flow direction of the scramjet were given. The characteristics of the shock structure and heat release rate were analyzed. The results show that the scramjet works in two different combustion modes under different flight conditions. When the scramjet is in the ramjet-mode operation, the pre combustion shock trains propagate to the front of the fuel injector, and the shock system in the combustor is relatively weak; as the shock train moves forward, the separation vortex structure is formed in the isolator, and the fuel is rolled up to the upstream. Part of the combustion is completed before the injector. The separation of the combustor mainly occurs inside the cavities, and the heat release is concentrated in the head of the first cavity. When the scramjet is in the scramjet-mode operation without shock train forward propagation, the shock system in the cavity section is relatively stronger and the fluctuation of flow parameters is more severe. The combustion occurs downstream of the injector, and the separation vortex in the combustor has a long flow span, forming a continuous flow separation from the leading edge of the first cavity to the second cavity. The separation vortex helps the combustion to propagate downstream, so the heat release is more evenly distributed along the flow direction of the combustor. The flow separation induced in the section between two cavities promotes the formation of the separation vortex with large flow direction span in the combustor, which may help the combustion to propagate downstream, so as to realize distributed heat release and avoid shock train propagation caused by concentrated heat release.