飞机结冰中水滴撞击特性的欧拉法准确性分析

Accuracy analysis of Eulerian method for droplet impingement characteristics under aircraft icing conditions

过冷水滴撞击特性计算是飞机结冰冰形预测与防除冰系统性能分析的基础,常用方法为欧拉法与拉格朗日法,2种方法的结果通常是一致的,但在某些部件上会出现差异。通过对欧拉法与拉格朗日法进行比较,分析2种方法结果的异同,进而讨论欧拉法对于飞机结冰中水滴撞击特性计算的准确性。以NACA 0012翼型、冰风洞风道、S形进气道与发动机气膜帽罩为对象,采用欧拉法与拉格朗日法计算获得水滴运动及局部水收集系数。结果表明:当水滴运动未受到上游效应影响时,欧拉法与拉格朗日法的结果一致;当水滴发生偏转后,欧拉法速度的单一性使水滴流线不能相交,而拉格朗日法能捕捉水滴轨迹的交叉,导致2种方法的预测产生差异,且欧拉法结果与水滴不碰撞及聚并的假设存在冲突;水滴在上游部件空气绕流或气流吹袭作用下都会发生偏转,使得欧拉法与拉格朗日法得到的下游表面水收集系数不相符,欧拉法对于S形进气道与发动机气膜帽罩的水滴运动及撞击特性计算存在误差。研究成果对飞机结冰冰形的准确预测及防除冰系统的设计有重要参考价值。

The calculation of super-cooled droplet impingement characteristics is the basis for the prediction of ice shape and the performance analysis of anti-icing and de-icing systems under icing conditions.Eulerian and Lagrangian methods are the commonly used ones,and their predictions are usually consistent.However,different results were found between the two methods for some aircraft components.In this paper,Eulerian and Lagrangian methods are compared to analyze the similarities and differences between the two results,and then the accuracy of Eulerian method for the calculation of the droplet impingement characteristics is discussed.Taking a NACA 0012 airfoil,an icing wind tunnel,an S-shape duct,and an engine cone with a hot-air film-heating anti-icing system as the research objects,the water droplet motion,and local water collection efficiency are calculated by Eulerian and Lagrangian methods.The outcomes demonstrate that the Eulerian and Lagrangian approaches produce consistent outcomes when the droplet motion is not influenced by upstream factors.After the water droplet deflections,the water droplet streamlines obtained by Eulerian method cannot intersect,while Lagrangian method can capture the crossing of droplet trajectories,which leads to the difference between the two methods.And the results of Eulerian method conflict with the assumption of no droplets collision or coalescence.The Eulerian method is not accurate for the calculation of water droplet motion and impingement characteristics of the S-shape duct and the engine cone with hot-air film-heating anti-icing system because water droplets will deflect under the influence of the upstream components and the airflow injection,making the collection efficiencies of the downstream surface obtained by Eulerian and Lagrangian methods inconsistent.This work is helpful for the accurate prediction of ice shape and the design of anti-icing and de-icing systems under aircraft icing conditions.