临界冰形确定方法及其对气动特性影响研究

临界冰形是指在适航规章结冰包线内，每个可用飞行构型下，对飞机操纵性和稳定性影响最严重的冰形，临界冰形分析是飞机适航取证中的重要工作。对临界冰形确定方法，及临界冰形对气动特性的影响进行了研究。发展了基于 CFD 方法计算临界冰形的一般方法，包括临界冰形分析状态、敏感性分析截面确定、结冰参数敏感性分析、临界结冰条件确定、临界冰形确定等。流场计算采用中航工业空气动力研究院气动力计算平台(UNSMB)，基于 Jameson 中心格式的有限体积法求解 N-S 方程；水滴撞击特性计算采用 Eulerian 方法求解水滴轨迹运动方程；结冰计算采用经典的 Messinger 热力学模型。选取 CRM 飞机为研究对象，以机翼外翼50%展长处为敏感性分析截面，在典型飞行条件下，分析了结冰对环境温度、水滴直径、飞行速度、飞行迎角等参数的敏感性。利用“几何外形敏感性分析方法”，即通过对比冰形的上下冰角角度和冰角厚度等冰形几何参数来确定最严重冰形，得到了CRM 飞机的临界结冰条件和临界冰形，其中敏感性分析截面在水滴直径为30μm 时上冰角厚度和下冰角厚度最大，冰角最大厚度约41 mm。计算了结冰后的气动性能衰减规律，临界冰形对飞机气动性能影响严重，导致升力降低6.7%~23.8%，阻力增加17%~70.9%。发展了45min 待机临界冰形确定方法，基于几何外形敏感性分析方法进行环境温度、水滴直径、飞行条件等各类参数的结冰敏感性分析，得到飞机的临界结冰条件和临界冰形，对于民用飞机设计和适航取证具有一定的工程应用价值。

Research on critical ice shape determination and its effects on aerodynamics

Critical ice shape determination method and its effects on aerodynamics were investigated.A typical tool used in the development and certification of an aircraft for flight-into-known-icing conditions is critical ice shapes.These shapes are developed for both the unprotected and protected surfaces of the aircraft.They are then used in dry-air testing to assess the likely worst case handling and performance of the aircraft in natural icing flight.Critical ice shapes are those with ice accretion geometries and features representative of that which can be produced within the icing certification envelope that result in the largest adverse effects on performance and handling qualities over the applicable phases of flight of the aircraft. A critical ice shape determination method was developed based on CFD approach,which was applied to critical ice shape condition analysis,sensitivity section determination,icing parameter sensitivity analysis, critical icing condition determination and critical ice shape determination.The flow field was calculated using CFD platform of AVIC Aerodynamics Research Institute (UNSMB),by solving N-S equation based on the finite volume method with Jameson central scheme.Impingement characteristic of droplets was calculated using the Eulerian method for the droplet trajectory equation,and classical Messinger thermodynamics model was applied to simulate ice growth. Sensitivity of ice shapes to parameters as ambient temperature,droplet diameter,and flight conditions were analyzed on Common Research Model (CRM)model,with the 50% spanwise wing section as the sensitivity analysis section.An airfoil sensitivity approach was applied to determine critical icing condition and ice shape for CRM, by comparing the ice geometry parameters such as ice horn angle and ice thickness.The 30 micron case has the largest and most after ice thickness and ice horn angle,the maximum ice thickness is about 41 mm.Regarding aerodynamic degradation due to calculated ice,critical ice shape affects seriously the aerodynamic performance of aircraft,causes that lift reduces by 17% ~ 70.9%,drag increases by 6.7% ~23.8%.The developed 45 minutes holding critical ice shape determination method can be used to numerically determine critical condition and ice shape,and is applicable in civil aircraft design and certification.