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高超声速溢流冷却是一种新型的飞行器热防护方法,基本思想为:在高热流区布置溢流孔,控制冷却液以溢流方式流出,之后通过飞行器表面摩阻作用展布为液膜,形成热缓冲层以降低飞行器表面热流。目前,溢流冷却技术还处于探索阶段,实现工程应用前还需开展大量的实验验证和机理研究工作。本文首次开展溢流冷却的实验研究工作,采用热流测量、液膜厚度测量及液膜流动特性观测技术,搭建了完善的溢流冷却风洞实验平台,对溢流冷却热防护性能和高超声速条件下液膜流动规律进行了初步研究。研究表明:(1)高超声速流场中通过溢流能够在飞行器表面形成液膜并有效隔离外部高温气流,可降低飞行器表面热流率;(2)楔面上的液膜前缘流动是一个逐渐减速的过程,增加冷却液流量液膜厚度变化不明显,但液膜前缘运动速度增加;(3)液膜层存在表面波,在时间和空间方向发生演化,导致液膜厚度的微弱扰动;(4)液膜层存在横向展宽现象,即液膜层宽度大于溢流缝宽度。原因是液膜层与流场边界层条件不匹配,存在压力梯度,迫使冷却液向低压区流动,从而展宽液膜层,并且流量越高,横向展宽现象越明显。
Hypersonic overflow cooling is a new type of thermal protection method for aircraft. The basic idea is that the overflow hole is arranged in the high heat flow area to control the flow of the coolant in an overflow manner, and then the liquid film is spread through the frictional effect of the aircraft surface, A thermal buffer layer is formed to reduce heat flux on the aircraft surface. At present, overflow cooling technology is still in the exploratory stage, and a great deal of experimental verification and mechanism research work needs to be carried out before engineering application. In this paper, the first experimental study of overflow cooling was carried out. The experimental platform of overflow cooling wind tunnel was set up by using the measurement of heat flow, the measurement of liquid film thickness and the observation of liquid film flow characteristics. The thermal protection performance and hypersonic conditions Under the film flow of a preliminary study. The results show that: (1) The flow field in hypersonic flow field can form a liquid film on the surface of the aircraft and effectively isolate the external high-temperature airflow, which can reduce the heat flux on the surface of the aircraft; (2) (3) The presence of surface wave in the liquid film layer evolves in time and space direction, resulting in the weak disturbance of the liquid film thickness; (3) (4) there is a horizontal stretching phenomenon of the liquid film layer, that is, the width of the liquid film layer is larger than the width of the overflow slit. The reason is that the liquid film does not match the boundary condition of the flow field, and there is a pressure gradient that forces the coolant to flow to the low pressure zone, thereby widening the liquid film layer. The higher the flow rate, the more obvious the horizontal stretching phenomenon.