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Scramjets and shock tunnels—The Queensland experience

机译：超燃冲压发动机和冲击隧道—昆士兰州的体验

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This article reports on the use of a shock tunnel to study the operation of scramjet powered configurations at sub-orbital velocities above 2 km/s. Thrust, as given by a net thrust equation, is used as a figure of merit throughout the study. After a short description of the shock tunnel used and its operating characteristics, experiments on the combustion release of heat in a constant area duct with hydrogen fuel are reviewed. The interaction between heat release in the combustion wake and the walls of the duct produced pressure distributions which followed a binary scaling law, and indicated that the theoretically expected heat release could be realized in practice, albeit with high pressure or long combustion ducts. This heat release, combined with attainable thrust nozzle characteristics and a modest level of configuration drag, indicated that positive thrust levels could be obtained well into the sub-orbital range of velocities. Development of a stress wave force balance for use in shock tunnels allowed the net thrust generated to be measured for integrated scramjet configurations and, although the combination of model size and shock tunnel operating pressure prevented complete combustion of hydrogen, the cruise condition of zero net thrust was achieved at 2.5 km/s with one configuration, while net thrust was produced with another configuration using an ignition promoter in hydrogen fuel. Nevertheless, the combination of boundary layer separation induced inlet choking and limited operating pressure levels prevented realization of the thrust potential of the fuel. This problem may be alleviated by recent increases in the shock tunnel operating pressures, and by promising research involving inlet injection of the fuel. Research on the drag component of the net thrust equation resulted from the development of a fast response skin friction gauge. It was found that existing theories of turbulent boundary skin friction predicted the skin friction when combustion of hydrogen occurred outside the boundary layer, but combustion within the boundary layer dramatically reduced the skin friction. Finally, for the first time in the world, supersonic combustion was produced in a free flight experiment. This experiment validated shock tunnel results at stagnation enthalpies near 3 MJ/kg.
机译：本文报道了使用冲击隧道研究超燃冲压发动机动力配置在2 km / s以上的亚轨道速度下的运行情况。由净推力方程式给出的推力，在整个研究过程中用作品质因数。在简短描述了所使用的冲击隧道及其运行特性之后，回顾了使用氢气燃料在恒定面积管道中燃烧释放热量的实验。燃烧尾流中的热量释放与导管壁之间的相互作用产生了遵循二元比例定律的压力分布，这表明理论上期望的热量释放可以在实践中实现，尽管使用高压或较长的燃烧导管。这种热释放与可获得的推力喷嘴特性和适度的配置阻力相结合，表明可以在速度的亚轨道范围内很好地获得正推力水平。通过开发用于冲击隧道的应力波力平衡装置，可以测量集成超燃冲压发动机构造产生的净推力，尽管模型尺寸和冲击隧道工作压力相结合可防止氢完全燃烧，但巡航状态为净推力为零在一种配置下，以2.5 km / s的速度达到最大功率，而在氢燃料中使用点火助推器以另一种配置产生净推力。然而，边界层分离引起的入口阻塞和有限的工作压力水平的组合阻止了燃料推力的实现。可以通过最近增加的冲击隧道工作压力以及通过涉及燃料的入口喷射的有前途的研究来缓解该问题。净推力方程的阻力分量的研究是由于快速响应蒙皮摩擦计的发展而引起的。已经发现，现有的湍流边界皮肤摩擦理论预测了当氢的燃烧发生在边界层外时的皮肤摩擦，但是边界层内的燃烧显着降低了皮肤摩擦。最终，世界上第一次在自由飞行实验中产生了超音速燃烧。该实验验证了在3 MJ / kg附近的停滞焓下的冲击隧道结果。

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