冰颗粒动力学和热力学特性研究及对发动机内部结冰的影响

Engine power-loss events have increasingly occurred in recent years, which included engine rollback, flameout, stall, as well as damage to the low pressure compressor from shed ice. It is now generally believed that the events result from the ice crystals ingestion by engine, which would partially melt and refreeze on internal components. Ice particles are mainly driven by aerodynamic force from the surrounding airflow and gravity, and the heat and mass transfer happen on the surface of the ice crystal. It is a typical multiphase flow phenomenon. More complex conditions may occur when the ice particles impinge on the surface of the engine components. So the characteristics of the ice crystals are distinctly different from the supercooled droplets. So far the mechanism of the kinetics and thermodynamics of ice crystal is not determined yet. . In order to clarify the mechanism of the engine internal icing caused by the ice crystal ingestion, the study concerns the dynamics and thermodynamics of the ice crystal. Firstly, the theoretical analysis including the effect of the airflow on the ice crystal, the impingement on the surface of the engine components and the heat and mass transfer when the ice crystal passing though the engine will be investigated. And the physical models of the engine internal icing phenomenon are obtained.Then the mathematical model is deduced from the physics. Based on the above analysis, the law of the movement,impinging,heat and mass transfer of the ice crystal is explained. Finally, Numerical method is applied to simulate the engine internal icing with the mathematical models and the results will be validated by experimental data in literature. This program is of great theoretical value to the investigation of power-loss events, providing theoretical foundation for evaluating the hazards to engines brought by ice crystals.

随着航空发动机推力损失事件的逐年增加，冰颗粒对航空发动机的威胁越来越受到人们重视，冰颗粒导致的发动机内部结冰已成为发动机安全运行的严重威胁之一。由于冰颗粒结冰不同于一般的过冷水滴结冰，其动力学、热力学及结冰机理尚不完全明确，因此冰颗粒结冰的研究亟待开展。本项目拟通过理论分析展开冰颗粒与空气相互作用机理、冰颗粒的传热传质规律、冰颗粒与结冰表面碰撞的相互作用关系、冰颗粒结冰热力学机理的研究，并以上述研究为基础，结合数值模拟的方法实现冰颗粒结冰的物理过程再现，数值模拟结果与文献中的实验结果对比以验证理论分析与数值模拟的正确性。通过研究阐明冰颗粒运动、碰撞、传热传质的规律，揭示冰颗粒的动力学、热力学特性以及引起发动机内部结冰的物理机理。本项目对高空发动机推力损失研究具有重要的理论价值，为评估冰颗粒对发动机的危害提供理论依据，对消除和减轻这一危害奠定理论基础。

航空发动机摄入冰颗粒导致的内部结冰已成为发动机安全运行的严重威胁之一，近年来对这一问题的研究已成为航空发动机结冰研究领域的一个热点。本项目针对航空发动机摄入冰颗粒结冰这一问题，开展了冰颗粒与空气相互作用研究，建立了冰颗粒-水滴-空气混合相计算模型，计算了球形冰颗粒和水滴的撞击特性以及球形和非球形冰颗粒的撞击特性，结果表明由于冰颗粒的直径较大其撞击极限大于水滴的撞击极限，与球形冰颗粒相比非球形冰颗粒更容易绕过叶片前缘进入发动机内部；开展了冰颗粒的传热传质研究，得到了冰颗粒直径与融化时间的关系以及融化过程中温度分布和冰水含量分布随时间的变化，研究表明冰颗粒完全融化时间随初始直径的增大而增加，冰颗粒穿过压气机时确有未完全融化的情况，这为压气机内部结冰提供了条件；开展了冰颗粒撞击结冰表面的分析，建立了冰颗粒撞击结冰表面的模型，计算了表面水膜对粘附冰颗粒的影响，结果表明水膜厚的地方粘附的冰颗粒多，随着水膜的减薄粘附的冰颗粒逐渐减少，可以看出表面水膜对冰颗粒粘附过程的影响明显；开展了冰颗粒结冰热力学过程研究，结合冰颗粒的撞击模型以及Messinger结冰热力学思想，建立了冰颗粒-水滴共存的混合相结冰热力学模型，开发了计算程序，计算了类似叶片部件的冰颗粒-水滴共存的混合相结冰，与文献中实验结果和计算结果进行了对比，结果表明由于冰颗粒在升温过程中吸收大量潜热使表面水膜冻结不产生溢流，因此冰颗粒-水滴共存的混合相结冰的冰形具有一定的霜冰特征，不同工况下计算冰形的结冰极限、生长趋势与文献中的实验结果均吻合良好且优于文献中的计算结果，对比结果验证了冰颗粒-水滴混合相结冰计算程序的正确性。本项目研究成果对深化冰颗粒摄入导致发动机内部结冰的认识，进一步认清冰颗粒摄入导致发动机内部结冰的机理，准确预测发动机内部结冰、评估冰颗粒对发动机的危害，提出有效措施消除和减轻这一危害等方面具有重要学术意义和工程实用价值。