Investigation on flow field characteristics of a rectangular scramjet in different combustion modes
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摘要: 为研究乙烯燃料矩形截面超燃冲压发动机不同燃烧模态下的流动特性，在直连式试验的基础上对冷流和不同当量比的4个状态进行了三维定常数值模拟，比较了试验和计算结果，选择了适用于本构型的模态判别准则，给出了流道内壁面压力、一维平均马赫数的沿程分布规律，分析了各状态下流场中波系结构、流动分离及燃烧的特征。研究结果表明：采用AHL3D对该发动机进行三维计算所得壁面压力与试验壁压吻合良好，试验与计算具有较好的一致性；未注油的冷态情况下流道内形成由多道斜激波与膨胀波组成的反射波系，壁面压力波动较大，波系分布主要受流道结构影响；纯超燃模态时，燃料喷射与主流相互作用使注油位处形成明显激波，压升起点固定在注油位之后，注油位波系对流场结构的影响较大，同时分离结构分布在整个凹槽内；双模态超燃时，流道内主导波系是激波诱导边界层分离形成的斜激波串结构，燃烧室内波系较弱，此时隔离段内激波串前缘后的角区出现分离，凹槽内分离区域减小；双模态亚燃时，随着逆压梯度激波串的前移，隔离段内角区的分离面积不断扩大，凹槽内分离区进一步缩小。发动机处于双模态超燃或双模态亚燃模态时，随着激波串结构的形成与前移，部分燃烧可能在隔离段内完成；而对于纯超燃模态，燃烧仅发生在凹槽与扩张段内，化学反应与高温区的分布相对更集中。Abstract: In order to investigate the flow field characteristics of an ethylene fueled rectangular scramjet in different combustion modes, three-dimensional steady Reynolds averaged Navier-Stokes simulations of the flowpath were employed on the basis of direct-connect experiments for four different equivalence ratios. The numerical and experimental results were compared. The distinguishing criterion of the combustion modes for this configuration was chosen. The regularities of the sidewall pressure and one-dimensional average Mach number distributions were discussed. And the detailed characteristics of the shock structure, the flow separation, and the combustion were analyzed. The results indicate that the simulation results are in excellent agreement with the ground-test data. Multiple reflections of the oblique shock waves and expansion fans result in the wall pressure fluctuation, and the shock system is mainly affected by the flowpath structure for Case Cold. In the scramjet-mode operation, the influence of the shock produced by the interaction between the flow and the injectors on the flow field is obvious, the pressure rise is anchored downstream of the injector, and the flameholder cavity is full of three-dimensional separated structures. In the dual-scramjet-mode operation, the oblique shock train induced by shock-boundary-layer interactions dominates the flow field structure, and the shock system is weak in the combustor. And some separation occurs closely behind the shock train leading edge in the corners of the isolator whereas the separated region reduces in the cavity. In the ramjet-mode operation, the shock features are similar to that in the dual-scramjet-mode operation. The separation regions expand in the isolator corner and reduce in the cavity with the upstream propagation of the shock train. Some combustion may occur in the isolator with the upstream propagation of the shock train for the dual-scramjet-mode and ramjet-mode operations, while in the scramjet-mode operation the combustion is conducted just in the cavity and expander, and the chemical reaction and high temperature distributions are more concentrated.
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Key words:
- scramjet /
- ethylene /
- combustion mode /
- shock system /
- separation
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图 3 试验与计算壁压对比
Figure 3. Comparison of computaional and experimental sidewall pressures
图 6 不同状态下发动机内Ma=1等值面及分离区示意图
Figure 6. Isosurfaces of Ma=1 and u=-0.001m/s for different cases
图 7 不同模态下流道内静温分布
Figure 7. Distributions of temperature along the flowpath for different modes
图 8 不同模态下流道内质量平均静温与二氧化碳沿程分布
Figure 8. Distributions of the mass average temperature and CO2 along the flowpath for different modes
图 9 不同模态下流道内CO2分布
Figure 9. Distributions of CO2 along the flowpath for different modes
图 10 Case2状态下流道内总温、二氧化碳及流线的局部分布
Figure 10. Distributions of the total temperature、CO2 and streamline along the flowpath for Case2
表 1 试验来流条件
Table 1. Experimental inflow conditions
Ma Tt/K pt/MPa γ Air 2.05 937 0.8 1.369 C2H4 1.00 300 
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