Mixing and Combustion Enhancement in Scramjet Combustors Induced by Interaction between Vortex and Shock Wave

为了建立一种评价超燃冲压发动机燃烧室中可用能量转化为推进功的增益和损失相对重要性的方法，引入了用动能效率和燃烧效率表示的燃烧室性能参数。参数中的这两种效率以推力方程中的形式组合在一起。利用已有的实验数据，对两种不同喷油方式的超声速燃烧室进行了燃烧室性能参数评估，明确了喷油方式、燃烧室长度、喷嘴内化学反应对燃烧室性能的影响。结果表明，基于该参数的最佳燃烧室长度小于仅根据燃烧效率或混合效率估算的燃烧室长度的一半。实验结果表明，用纯净空气的特性来代替污浊空气的特性，可以得到更大的性能参数值。作为涡旋与激波相互作用的典型流场，选取了过膨胀和欠膨胀条件下的可压缩旋涡射流，并对其混合进行了实验研究。首先将0.3、1.0或2.0马赫的非旋涡射流注入静止大气或加热亚音速气流中。在保持气流推力不变的情况下，采用膨胀或压缩假设得到的直径和速度参考值对数据进行无量纲化处理，非理想膨胀非旋涡射流的混合特性与理想膨胀射流的混合特性具有较好的相关性。旋流射流是通过在喷嘴的亚音速部分附加一个旋流器产生的。随着旋流数的增加，射流的混合性能略有增强。与理想膨胀射流相比，非理想膨胀旋涡射流的潜在核心区缩短，但其在发达区域的混合速率减慢。利用流动显示技术观察了涡旋对平行超声速射流混合的影响。旋流增强了双喷流合并区附近的混合。同一方向的旋流对两种射流的混合效果优于相反方向的旋流。少

In order to establish a method to evaluate relative importance of gain and loss in the available energy to be converted into the propulsive work in the scramjet combustor, we introduced a combustor performance parameter which was written in terms of the kinetic energy efficiency and the combustion efficiency. These two efficiencies in the parameter were combined in the form appearing in the equation for thrust. The combustor performance parameter was evaluated with the available experimental data for two supersonic combustors with eight fuel injection patterns, and it clarified the effects of injection pattern, combustor length, chemical reaction in the nozzle were investigated. The result showed that the optimum combustor length based on the parameter was less than a half of one estimated only from the combustion efficiency or the mixing efficiency. It was found that use of the properties of pure air instead of those of vitiated air used in the experiment may results in significantly … More different value of the performance parameter.As a typical flowfield where interaction between vortices and shock waves occurs, compressible swirling jet of over- or under-expansion condition was chosen, and mixing of such jet was experimentally investigated. At first, non-swirling jet of Mach 0.3, 1.0 or 2.0 was injected into quiescent atmosphere or heated subsonic flow. Mixing characteristics of the non-ideally expanded non-swirling jets could be well correlated with those of the ideally expanded jets when the reference values of diameter and velocity calculated with assumption of expansion or compression to ambient pressure keeping the stream thrust constant were used to non-dimensionalize the data. The swirling jet was produced by attaching a swirler in the subsonic portion of the nozzle. Mixing of the jet was slightly enhanced by increasing swirl number. In comparison with the ideal expansion jet, the potential core region of the non-ideally expanded swirling jet was shortened, but its mixing rate in the developed region was retarded. Effect of swirl on the mixing of two parallel supersonic jets were observed by flow visualization. The swirl enhanced mixing near the merging region of the twin jets. Swirl of the same direction for both jets had resulted in better mixing then that of the counter direction. Less