耦合多源非稳态条件下液氮喷嘴内空化流动及雾化特性机理研究

Liquid nitrogen spray cooling technology in cryogenic wind tunnel has excellent cooling performance and can achieve both the large Reynolds number and Mach number at the same time. However, the liquid nitrogen supply system is unstable and the external condition of the spray nozzle is changing with the operation condition. Due to the multisource unstable factors, the microscopic cavitating flow characteristics, the macroscopic flow characteristics and atomization characteristics within a spray nozzle become very complicated, which makes it very challenging to obtain the effective cooling performance and high-precision temperature control for the liquid nitrogen spray cooling system in cryogenic wind tunnel. In this study, the numerical models will be established to describe the cavitating flow and the atomization, and the experiments will be performed to investigate the cavitating flow characteristics, the flow characteristics and atomization characteristics. The multisource unstable factors and the unstable external condition will be properly considered in both the numerical and experimental studies. The methodologies will be developed to study the microscopic and macroscopic characteristics of the spray nozzle, and the influence of the multisource unstable factors and the unstable external condition on the cavitating flow characteristics and the atomization characteristics will be revealed. The results and findings in this sudy could provide theoretical and engineering guidelines for the construction of the cryogenic wind tunnel.

液氮喷雾冷却技术可有效实现大空间降温，同时满足低温风洞大雷诺数和大马赫数条件气动实验需求。低温风洞液氮喷雾系统受非稳态入口条件和喷嘴外部流场的影响，其喷嘴内部微观空化流动、宏观流量及雾化特性十分复杂，为低温风洞液氮喷雾系统的高效冷却和高精度温度调控带来巨大挑战。本项目拟在充分考虑液氮喷雾冷却系统耦合多源非稳态特性和外部非恒定换热条件的基础上，建立液氮喷嘴空化流动和雾化模型，开展耦合非稳态扰动和复杂多变外部流场条件下喷嘴内部液氮空化流动、流量特性和雾化特性的研究，通过理论和实验相结合的方式掌握非稳态和非恒定条件下液氮喷嘴宏观和微观特性的研究方法，揭示喷嘴前端液氮供液系统的非稳态特性及喷嘴外部风洞气流的非恒定特性对喷嘴内部空化流动和雾化特性的影响规律。最终为我国大型低温风洞系统建设提供理论依据和关键技术支撑。

液氮喷雾冷却是通过降低风洞内气流温度提高飞行雷诺数以确保飞行器模拟实验准确性的关键技术。为实现低温风洞液氮喷雾系统的高效冷却和高精度温度调控，本项目进行了非稳态入口条件和喷嘴外部流场对喷嘴内部微观空化流动、宏观流量及雾化特性影响的研究。本研究的主要内容为（1）低温风洞液氮喷嘴内部非稳态空化流动机理研究。（2）非稳态条件下低温风洞液氮喷嘴雾化特性研究。（3）耦合多源非稳态条件及非恒定外部换热边界的低温风洞液氮喷嘴流动及雾化特性研究。本课题的重要结果（1）在充分考虑液氮喷雾冷却系统耦合多源非稳态特性和外部非恒定换热条件的基础上，建立了液氮喷嘴空化流动和雾化模型，开展了耦合非稳态扰动和复杂多变外部流场条件下喷嘴内部液氮空化流动、流量特性和雾化特性的研究。（2）完成了文丘里管内制冷剂空化流动可视化实验研究，获得了不同入口压力以及流体温度下空化区域产生、发展和脱落的周期性规律，实验数据可为低温流体空化流动的研究提供一定的参考。（3）建立了低温风洞全工况模拟液氮喷雾实验系统，进行了耦合多源非稳态及非恒定外部条件液氮喷雾流动及雾场特性进行可视化实验研究，获得了实际工况下液氮雾化特性、雾场参数以及空间冷却性能。关键数据及其科学意义（1）通过理论和实验相结合的方式掌握非稳态和非恒定条件下液氮喷嘴宏观和微观特性的研究方法，获得了喷嘴前端液氮供液系统的非稳态特性及喷嘴外部风洞气流的非恒定特性对喷嘴内部空化流动和雾化特性的影响规律。（2）为解决大型低温高雷诺数风洞建设中的关键技术提供重要依据。