高超声速飞行器横向缝隙内部涡旋结构及热环境数值模拟研究

发布时间：2018-12-17 18:21

【摘要】：航天飞机和X-37B等长时间再入式高超声速飞行器在飞行过程中需要克服严重的气动加热,为容纳由此引起的结构间热膨胀,防热瓦之间必须预留一定的缝隙。另外,为了能够顺利完成变舵偏、部件弹出等飞行动作,缝隙的存在同样不可避免。缝隙的存在将导致飞行器表面局部流场结构及传热特性发生较大变化,缝隙入口处由于边界层分离与再附将产生局部高热流区;在某些工况下缝隙入口处会产生激波;缝隙内会卷起涡旋结构等。涡旋结构将大量热量卷入缝隙中,使得对流传热明显增强,加之缝隙极其狭小,辐射散热效应受阻,缝隙内壁极易产生较高的壁温,进而引起较为严重的局部烧蚀。因此,认识高超声速飞行器缝隙内的流场结构,研究来流参数、几何参数等对缝内涡旋结构及壁面热流分布的影响极为重要。世界各航天大国均对缝隙流动进行了研究,如美国在研制航天飞机时,曾投入了巨大的人力物力进行防热瓦缝隙热环境和热结构试验。但受限于数值计算技术的发展,早期主要依靠地面试验进行研究,成本较高,周期较长。本文针对这一问题,利用自主研发的CFD软件,对高超声速飞行器缝隙流动进行了较为精细的数值模拟研究。首先重点阐述了在缝隙流动机理分析、试验测量以及数值模拟方面取得的成果及存在的不足。针对这些不足和缝隙流动的特点,在van Leer通量分裂的基础上引入了焓守恒修正,很好地改善了van Leer通量分裂方法在边界层、剪切层中耗散过大的问题,有效提高了缝隙中的流场分辨率。在此基础之上分别从涡旋结构和壁面热流两个方面对本文的计算方法进行了有效性验证,并发现合理捕捉旋涡结构对于缝隙壁面热流的准确模拟具有重要意义。接着对缝隙流动机理进行了分析。针对平板模型上的无限长缝隙,从涡量的角度出发,分析了缝隙内涡旋结构的形成、发展及耗散过程,并得出缝内的黏性耗散作用对缝隙流动的研究至关重要。结合机理分析,研究了来流参数、几何参数对缝隙流动的影响。给出了缝内涡旋结构及壁面热流随来流雷诺数、马赫数、迎角、缝隙深宽比及缝隙倒圆半径的变化规律,得出了缝内主涡个数是否满足与缝隙深宽比大致成正比的一个判别准则,其结论可为防热设计提供参考。最后对全文的研究工作及得到的相关结论进行了归纳总结,并对论文中存在的不足和下一步的研究方向进行了简要阐述。
[Abstract]:The space shuttle and X-37B long-time reentry hypersonic vehicle need to overcome the severe aerodynamic heating in flight. In order to accommodate the thermal expansion between the structures caused by it, a certain gap must be reserved between the heat resistant tiles. In addition, the existence of cracks is also inevitable in order to successfully complete the variable rudder deviation and the ejection of components. The existence of the gap will lead to great changes in the structure of the local flow field and the heat transfer characteristics of the aircraft surface. The gap entrance will produce a local high heat flux region due to the separation and reattachment of the boundary layer, and a shock wave will occur at the gap entrance under some working conditions. The vortex structure will be rolled up in the crevice. The vortex structure involves a large amount of heat in the gap, which makes the convection heat transfer obviously enhanced, and the gap is extremely narrow, the radiation heat dissipation effect is blocked, and the inner wall of the gap easily produces higher wall temperature, which leads to serious local ablation. Therefore, it is very important to understand the structure of flow field in the slot of hypersonic vehicle, and to study the influence of the parameters of incoming flow and geometry on the vortex structure and the heat flux distribution on the wall. The gap flow has been studied in all the major spaceflight countries in the world. For example, the United States has invested huge manpower and material resources to test the thermal environment and thermal structure of the slot in the space shuttle. However, limited by the development of numerical calculation technology, the early research mainly depends on the ground test, which has high cost and long period. In order to solve this problem, a detailed numerical simulation of slot flow in hypersonic vehicle is carried out by using CFD software developed by ourselves. Firstly, the achievements and shortcomings in the analysis of slot flow mechanism, experimental measurement and numerical simulation are described. In view of these shortcomings and the characteristics of slot flow, the enthalpy conservation correction is introduced on the basis of van Leer flux splitting, which improves the problem of excessive dissipation of van Leer flux splitting method in the boundary layer and shear layer. The flow field resolution in the slot is improved effectively. On this basis, the validity of the method is verified from the vortex structure and the wall heat flux, and it is found that the reasonable capture of the vortex structure is of great significance for the accurate simulation of the gap wall heat flux. Then the mechanism of slot flow is analyzed. In this paper, the formation, development and dissipation process of vortex structure in the plate model are analyzed from the point of view of vorticity, and it is concluded that the viscous dissipation in the slot is very important to the study of slot flow. Based on the mechanism analysis, the effects of flow parameters and geometric parameters on slot flow are studied. The variation of vortex structure and wall heat flow with Reynolds number, Mach number, angle of attack, slit depth to width ratio and the radius of the reverse circle of the slot are given. A criterion for determining whether the number of main vortices in a slot is in direct proportion to the ratio of slit depth to width is obtained. The conclusion can be used as a reference for the design of heat protection. Finally, the research work and related conclusions are summarized, and the shortcomings of the paper and the next research direction are briefly described.
【学位授予单位】：中国空气动力研究与发展中心
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：V445.1;V416

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