飞机表面过冷大水滴撞击扰动对结冰演化的影响机理研究

The aircraft icing safety and airworthiness certification in supercooled large droplet (SLD) conditions has been of great importance in the development of large transport aircraft in China. However the technologies for icing prediction and anti-icing design is not adequate. An important reason is that current aircraft icing theory which based on steady heat and mass transfer hypotheses can not well predict the abnormal runback icing phenomenon of SLD. Resent research has revealed that the evolution of icing morphology and velocity is sensitive to disturbance. However the knowledge about the icing process of supercooled water droplet in impinging is not enough for us to understand the SLD icing law. The difficulty of research is the high-speed impinging of SLD is hard to simulate in experiment, and the law of SLD icing is not well recognized. This project selects the effect of droplet-impinging-disturbance on the icing evolution as the focal point. By developing the key technologies of observing the ice growth on a substrate and controlling the supercooled large droplets generation, an experiment is designed to study the mechanism that how the impinging dynamics changes the ice growth (i.e. pattern and velocity) on substrate. The effects of impact disturbance on substrate ice growth and stability are investigated with the phase transition theory of supercooled droplet on substrate. Then the icing evolution theory in supercooled droplet impinging is introduced. Finally the theoretical model of SLD icing prediction on aircraft is given by the investigation of aircraft icing simulation in SLD conditions. The achievement by this project is expected to improve the research on supercooled water droplet icing in impinging, and also improve the SLD icing perdition and anti-icing design technologies, which support the progress of icing safety airworthiness technology for the airplane in our country.

过冷大水滴(SLD)环境中的防冰与适航取证是我国大型飞机研制中的关键问题，但相关理论与技术仍不完善，特别是基于稳态传热传质的结冰基础理论无法有效预测SLD的异常溢流结冰现象。近期研究发现冰微观形态和生长速度的演化对扰动敏感，而SLD快速撞击条件下的结冰过程认知较少。研究难点在于大粒径过冷水滴高速撞击实验模拟困难，且结冰过程难于观察和分析。本项目以SLD撞击影响壁面结冰演化过程为切入点，结合机理实验与微观结冰理论研究飞机SLD结冰异常的机理。首先解决过冷水滴发生控制及撞击结冰观测技术，实验研究过冷水滴撞击对冰形态和生长速率的影响规律。接着理论研究水滴撞击条件下的冰生长和界面稳定性，揭示过冷水滴撞击扰动影响冰生长演化的机理，最后建立飞机SLD结冰预测模型并实验验证。本项目预期可以更深入认识过冷水滴撞击结冰机理，建立更准确的SLD结冰预测模型，支持我国飞机防冰及适航取证技术的发展。

针对过冷大水滴(SLD)环境标准的防冰设计和适航取证已成为当前国产大型民机走向国际市场的关键一环，其中的重点是发展可靠的结冰预测与防冰设计工具。而准确预测SLD结冰规律的关键是理解其撞击运动导致异常结冰速率的机制。本项目开发了过冷大水滴可控发生装置和实验方法，实验研究真实的大粒径过冷水滴撞击壁面结冰演化过程。研究发现不同于常温水滴撞击冷表面的单一冻结形态和线性温度-结冰速率关系，过冷水滴撞击壁面时冻结形态随过冷度和壁面特性有多阶段的演化，相对应的结冰速率和过冷度有着分段线性的关系。通过建立水滴碰撞运动、多阶段结冰演化和非稳态传热过程耦合的理论模型，分析水滴运动和结冰特征时间相对关系，分析水滴冻结速率和时间的关系，发现SLD碰撞中存在水平冰铺展和非稳态传热双重增强结冰速率的机制。据此建立了SLD碰撞扩散增强结冰理论与模型，可统一描述从SLD碰撞增强结冰到常规溢流结冰的不同结冰状态，有效预测SLD撞击结冰速率的演化过程，完成SLD碰撞结冰速率的机理实验对比验证，丰富完善了过冷大水滴结冰理论。基于对飞机SLD结冰适航研究现状的分析,项目开发了SLD双峰分布环境的高效模拟计算方法,连同建立的SLD结冰理论模型一起改进结冰模拟软件SJTUICE，实现SLD大跨度水滴分布结冰形状的准确预测，服务于国产大型民机的SLD防冰设计与适航取证研究。