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FD-21风洞冲压发动机Ma10流场与乙烯燃烧建立过程

ESTABLISHING PROCESS OF SCRAMJET FLOW AND ETHYLENE-BURNING AT Ma10 CONDITIONS OF FD-21 SHOCK TUNNEL

  • 摘要: 针对高焓激波风洞冲压发动机试验过程中流场建立与燃料点火、火焰传播、稳定之间存在强耦合以及风洞膜片烧蚀污染问题, 采用壁面测压与激发态OH*/CH*基化学发光光谱诊断相结合的手段, 探讨了长2 m、三维曲面压缩、带双侧凹腔的超燃冲压发动机在FD-21风洞Ma10模拟条件下有无乙烯燃料喷注时的流场建立过程, 阐述了风洞起动过程中的膜片烧蚀干扰情况, 揭示了点火、火焰稳定过程中OH*, CH*基时空分布与壁面压力关联特征, 精细化给出了冷热态发动机壁面沿程静压分布. 无燃料喷注的冷态通流条件下OH*, CH*基时空变化图像表明风洞膜片烧蚀污染主要存在于发动机流场建立初期的1 ms内. 乙烯喷注时OH*, CH*基时空变化发光图像表明发动机流场建立初期2 ms内会产生大量的自由基, 之后CH*基浓度下降至相机不可探测范围、OH*基浓度则维持在较为平稳的水平, 燃烧趋于动态稳定状态. 冷热态发动机壁面沿程静压分布存在倍数差异, 乙烯喷注时自喷注位置下游第一个测点开始出现压力跃升、直至尾喷管出口附近才膨胀至与冷态接近, 热态壁面压力约为冷态的2倍, 冷热态取样时间内的压力波动幅度近似一致、均小于10%, 与冷热态压升幅度存在数量级上的差异. 这些数据表明FD-21风洞可开展高超声速气流中的乙烯燃烧试验.

     

    Abstract: To explore the practicability of the free-jet experimental study on the scramjet fueled hydrocarbon, several tests of a three-dimensional scramjet were conducted at Ma10 simulated conditions of FD-21 piston-driven high enthalpy shock tunnel. The test article was the scramjet including a curved-surface compression inlet, a nearly constant rectangular-section isolator, a little divergent combustor with a cavity and a nozzle with the cross-section transition of rectangle to circle. The chemiluminescence visualization of the excited OH*/CH* radical along with the wall pressure measurement was developed to study the establishing process of scramjet flow and ethylene-burning. The temporal and spatial images of OH*/CH* in the combustor, together with the scramjet bodyside wall pressure data, were obtained for the tare without fuel injection and the ethylene injection conditions. For the tare condition, the OH* and CH* radicals in the combustor only exist at the first 1 ms period of the scramjet flow setup process, and the wall pressure of all taps tends to a plateau after a sharp increase at the air-flow arrival, revealing that the contamination of the diaphragm ablation can be ignored and a quasi-steady flow can be achieved. For the ethylene injection condition, a large number of OH* and CH* radicals emerge at the first 2 ms period of the scramjet flow setup process and then tend to a pseudo constant of a low OH* and an undetected CH* radical concentration, in spite of the wall pressure feature almost identical to that for the tare case. Additionally, the dramatic difference was achieved in the scramjet wall pressure distributions for the tare and the ethylene injection conditions, which was several orders of magnitude greater than the pressure fluctuation of the sample time interval. These evolving features of OH*/CH* radical and wall pressure data indicate an achievement of ethylene burning in hypervelocity flow, and the freejet experiment of a high Mach number scramjet fueled ethylene can be performed in FD-21 shock tunnel.

     

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