溢流液膜厚度测量方法及冷却机理研究

With the development of hypersonic vehicle, aerodynamic layout with high lift-drag ratio has been the mainstream in order to meet the aerodynamic force needs, leading to thermal protection become a bottleneck limiting aircraft design. For traditional passive and semi passive cooling method can’t meet the demand of thermal protection, active cooling technique should be combined to improve protection ability. The cooling mechanism of overflow liquid film cooling is similar with transpiration cooling. But the liquid film is formed with the effect of aerodynamic friction. It will lower the requirement of materials strength and difficulty of the cooling fluid pumping system, and has more engineering application prospects. The process of overflow liquid film cooling is accompanied with complicated heat and mass transmission. As a basic parameter, it is very important to research how to measure the film thickness. It helps to reveal the liquid film forming conditions, promote the film cooling mechanism research and evaluate cooling performance reasonably. This study will develop a liquid film thickness measuring method based on the conductance principle. With the liquid film thickness, the coolant transfer and evaporation process characteristics will be confirmed. Combine with the heat flow and flow field parameters, we will carry out research about liquid film forming conditions and cooling mechanism and provide a new method for hypersonic flight vehicle thermal protection.

随着高超声速飞行器的发展，为满足气动力需求高升阻比气动布局成为主流，进而导致气动热防护成为限制飞行器发展的瓶颈。传统的被动与半被动冷却方法不能满足热防护需求，需要结合主动冷却提高防护能力。溢流液膜主动冷却通过绕流气体表面摩阻作用实现液膜的展布，其冷却机理与发汗冷却相似。然而这种方法大幅降低了对材料强度的要求以及冷却液泵送系统的难度，更具有工程应用前景。溢流液膜冷却过程伴随着复杂的传质、传热现象，厚度作为最基本的特征参数，开展其测量方法的研究有助于揭示液膜形成条件，促进液膜冷却机理研究，合理评价冷却性能。因此对高超声速气流中几十到几百微米量级液膜厚度进行精确测量至关重要。本研究拟采用电导法的基本原理，发展液膜厚度测量方法，在此基础上获得冷却液传质、蒸发过程的特性，进而结合表面热流、风洞流场参数，研究溢流液膜形成条件及防热规律，为高超声速飞行器热防护提供一种新方法。

高超声速溢流冷却是一种新型的飞行器热防护技术，液膜厚度作为最基本的参数，对研究液膜形成条件、冷却机理及冷却性能评估等方面具有重要的意义。本项目研究内容为：1）提出利用电导法测量高超声速溢流液膜厚度。2）结合电磁学基本理论，对电导探头的数值仿真方法进行了研究，确定了电导探头的设计规则。3）研制了液膜厚度测量系统及附属的探头标定系统、冷却液注入系统、时序控制等实验系统，综合利用液膜厚度测量装置、纹影仪、热流测量技术、高速摄影、数字图像处理及时序控制技术，搭建了溢流冷却风洞实验平台。4）在高超声速条件下，开展了典型外形模型的溢流冷却实验，测量得到了液膜厚度变化历程，验证了电导法测量溢流液膜厚度的可行性。结合液膜流动图像和热流数据，验证了溢流冷却应用于高超声速飞行器热防护的可行性，并对溢流液膜流动特性、液膜对飞行器流场结构的影响及液膜流动影响因素进行了详细研究。