Fundamental Study on Scram Jet Engines

为了实现SCRAM喷气发动机这一最有前途的空间飞机和高超声速运输机的推进系统，本课题针对进气、燃油喷射与混合、超音速燃烧、热防护结构与材料四个重要领域进行了基础性研究。(1)在进气研究中，重点研究了进气口的稳定运行、机身边界层向发动机内流动引起的复合堵塞现象和瞬时不启动与再启动现象。结果表明，机身边界层流动容易导致发动机不启动，而后掠侧整流罩进气道容易从未启动恢复到重新启动。(2)燃油喷射与混合研究对超音速气流中燃油的流动力学和湍流混合过程有了进一步的认识。进行了二维和三维喷射实验，明确了混合效率与总压损失之间的关系。建立了二维喷射模型的数值模拟技术。(3)超音速燃烧的目的首先是实现氢气在超音速气流中的燃烧，其次是研究控制超音速燃烧过程的因素的重要性。在实验中，采用了平行流动和垂直流动两种喷射方式，通过对激波和火焰结构的光学观察，明确了燃烧对流动力学的影响。(4)在热防护结构和材料领域，将热管的概念应用于二维壁板，构建了一种高性能的冷却结构，并对其基本特性进行了研究。在高温材料的研究中，重点研究了陶瓷的断裂力学，特别是晶界强度与温度的关系。

In order to realize the SCRAM jet engine which is the most promising propulsion system for space planes and hypersonic transports, this research project aims at fundamental study in the four important fields :(1) Air intake, (2) Fuel injection and mixing, (3) Supersonic combustion, and (4) Thermal protection structure and materials.(1) In the air intake research the focus was put on the stable operation of inlets, and compound choking phenomena due to sucking of airframe boundary layer flows into engine and transient unstart and restart phenomena were investigated. Results show that the airframe boundary layer flow easily leads engines unstart, but that the swept side cowl inlet easily recovers from unstart to restart.(2) The study on fuel injection and mixing progressed understandings on flow mechanics and turbulent mixing process of fuels injected into a supersonic stream. Two-dimensional as well as three-dimensioanl injection experiments were conducted, and the correlation between mixing efficiency and total pressure loss were clarified. Numerical simulation technique for a two-dimensional injection model was established.(3) The purpose of supersonic combustion is first to realize combustion of hydrogen in the supersonic stream, and secondly to study importance of factors which control supersonic combustion processes. In the experiments parallel-to-flow injection as well as normal-to-flow injection were adopted, and the effect of combustion on flow mechanics were made clear via optical observation on the structure of shock waves and flames.(4) In the field of thermal protection structure and materials, a high performance cooling structure was constructed applying the heat pipe concept to a two-dimensional panel, and its basic characteristics were studied. In the research for high temperature materials, the fracture mechanics of ceramics were investigated especially on the relation between the strength of grain boundaries and temperature.