畸变气流影响下复合材料隔离段中激波串流动机理研究

In order to withstand the high aerodynamic heating during a long hypersonic flight and heat release of the combustion chamber, the scramjet isolator requires the use of thermal protective composites. Limited by the level of processing technology and the impact of high temperature ablation, there is a very rough and loose wall surface of the current composite isolator, sometimes airflow may penetrate into the outer wall, so it will have a great effect on the flow near the wall. In addition, the serious non-uniform features exist on the entrance of isolators, and it affects the performance of the isolator coupled with rough surfaces, and then affects the overall performance of the scramjet engine. So, it is very important to find out the flow mechanism of the composite isolator’s shock train considering the effect of the distorted flow. To address the above problems, this application will investigate the flow mechanism of the composite isolator’s shock train under the distorted flow through theoretical analysis and direct connect wind tunnel experiment, such as the shape of shock train, the maximum back pressure, Waltrup correlation and self-oscillation of the shock train. And it also pays close attention to the development situations of the boundary layer on the rough loose surface and the details of shock train through fine flow field measurements, in order to study the mechanisms of the composite isolator’s shock train with rough surface, and provide a scientific basis for the further understanding of the internal flow characteristic of the composite isolator’s shock train with rough surface.

为了承受高马赫数长时间飞行时的气动加热以及燃烧室的热释放，超燃冲压发动机隔离段需要采用热防护复合材料，受加工工艺水平所限以及高温烧蚀的影响，目前的复合材料隔离段内壁面粗糙疏松，严重时可能会有气流渗透，这会对隔离段的近壁区流动有很大的影响。另外，隔离段进口流场畸变程度严重，与这种特殊材质壁面耦合影响着隔离段的性能，进而影响超燃冲压发动机的整体性能。因此，深入认识畸变气流影响下的C-SiC复合材料隔离段的流动特机理就显得十分重要。针对上述问题，本项申请通过理论分析和直连实验研究畸变气流影响下的复合材料隔离段稳态特性和动态特性，如激波串形态、耐反压能力、激波串长度预测和激波串的自激振荡等，而且还将通过流场精细测量实验获得这种特殊材质壁面的附面层发展情况和激波串细节等流动特征，获得复合材料隔离段中激波串流动机理，为深入认识畸变气流影响下的复合材料隔离段内部流动特征提供科学依据。

本项目以超燃冲压发动机工程化过程中出现的C-SiC隔离段烧蚀问题为背景，通过理论分析、数值模拟和隔离段实验研究了畸变气流影响下的C-SiC复合材料隔离段内激波串的稳态特性、动态特性和激波串精细结构，首次获得了烧蚀后的C-SiC隔离段内激波串稳态特性，如壁面压升规律、耐反压能力、隔离段出口流动图谱和总压恢复系数等，采用无量纲不平度hs/Dhy来表征烧蚀后C-SiC隔离段内壁面严重不规则粗糙特征,并改进了经典的Waltrup公式，使之能够预测烧蚀后的C-SiC隔离段内激波串长度，精度得到大幅提高；首次获得了烧蚀后的C-SiC隔离段内激波串以及附面层发展形态，量化对比分析了烧蚀后的C-SiC隔离段与光滑不锈钢隔离段的激波串偏置程度与附面层厚度等，烧蚀后的C-SiC隔离段壁面不平度确实影响了近壁区流动，导致附面层增厚非常明显，激波附面层相互作用程度加深。首次获得了烧蚀后的C-SiC隔离段内激波串自激波振荡特性和激波串前传特性，烧蚀后的C-SiC复合材料不平度对激波串动态特性无影响。这些成果可以直接应用于工程化的超燃冲压发动机C-SiC隔离段的设计。