Abstract Cavities are commonly employed in scramjet combustors for flameholding and mixing enhancement, but the mechanism used to enhance mixing is absent at high supersonic Mach numbers, limiting their operational scope. The present study investigates the ability of crescent-shaped cavities placed upstream of a fuel injector to enhance mixing through vorticity generation, a mixing enhancement mechanism that is also effective at high supersonic Mach numbers. The mixing performance of five crescent cavity designs, two of which incorporate hybrid fuelling, is investigated using unsteady Reynolds-Averaged Navier–Stokes (URANS) computations of a chemically frozen flow with hydrogen as the fuel. It is found that the crescent cavities enhance mixing by up to 22.6% without the hybrid fuelling arrangement and by up to 90.1% with the hybrid fuelling arrangement. While vertical jet penetration is lower for all cavity cases, lateral penetration is higher and the cavity cases incur no or negligible total pressure loss compared to the baseline at the domain outflow, within the margin of error. Wall drag is also lower than in the baseline for some cavity cases. The primary mechanism driving mixing is found to be enhanced streamwise vorticity in the vicinity of the cavity, caused by the cavity vortex leaving the cavity and wrapping around the injector. The cavity flowfields are also found to be oscillatory in nature, although the oscillations are lateral and the harmonic frequencies are much lower than those of the longitudinal oscillations characteristic of conventional cavity flow. The mechanisms driving these oscillations are discussed, as are the flowfields for the best performing cavity cases. Several flowfield features of the crescent cavities are also highlighted and discussed, demonstrating how the hybrid injection cavity cases enhance mixing.

中文翻译：

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超燃冲压发动机燃烧室燃料与上游新月形腔混合的数值研究

摘要 空腔常用于超燃冲压发动机燃烧室的火焰稳定和混合增强，但在高超音速马赫数下，用于增强混合的机制不存在，从而限制了其操作范围。本研究调查了位于燃料喷射器上游的月牙形腔体通过涡度产生增强混合的能力，这种混合增强机制在高超音速马赫数下也有效。五个月牙形腔设计的混合性能，其中两个包含混合燃料，使用非定常雷诺平均纳维 - 斯托克斯 (URANS) 计算以氢为燃料的化学冻结流进行研究。研究发现，在没有混合燃料装置的情况下，月牙形腔将混合提高了 22.6%，提高了 90%。1% 与混合燃料安排。虽然所有空腔情况的垂直射流穿透较低，但横向穿透较高，与域流出处的基线相比，空腔情况不会产生或产生可忽略的总压力损失，在误差范围内。对于某些空腔情况，壁阻力也低于基线。发现驱动混合的主要机制是在空腔附近增强的流向涡量，这是由空腔涡流离开空腔并环绕喷射器引起的。还发现腔流场本质上是振荡的，尽管振荡是横向的并且谐波频率远低于常规腔流的纵向振荡特征。讨论了驱动这些振荡的机制，性能最好的腔体情况的流场也是如此。还强调和讨论了新月形腔的几个流场特征，展示了混合注入腔情况如何增强混合。