The Study On Aircraft Abnormal Icing Rate And Synergistic Change Of Ice Induced Aerodynamics

Aircraft icing has always been one of the key issues of aircraft design and aircraft airworthiness,but serious icing accidents still occur from time to time.In 1994,the Roselawn icing crash and subsequent serious of accidents showed that the aircraft will encounter abnormal icing in the environment of supercooled large water droplet larger than 100?m and will have rapid icing,runback ridge ice and rapid aerodynamic decline characteristics.At present,the United States Federal Aviation Administration?FAA?has issued 140 amendments to add the large water droplet environment into the icing airworthiness requirements.At the same time,the research has partially revealed the abnormal icing mechanism and its aerodynamic response,but the abnormal icing rate and the synergistic change of ice-induced aerodynamic with environment conditions have not been fully revealed.Focusing on the above problems,this paper expanded the range of supercooling of ice growth rate model.Based on the results,the synergistic change law of ice induced aerodynamics with variable environment condition was explored,and the aerodynamic response and decline caused by abnormal icing under certain conditions were explored.The details are as follows:Firstly,the morphology and velocity law of ice dendritic growth under different degrees of supercooling were simulated through the phase field method.The ice growth pattern has a dendritic feature.When the degree of supercooling is greater than 20K,the power law of the velocity law changes from 2.09 to 3.47,which reflects the rapid growth.Then the rapid growth phenomenon was explained by two key influencing factors:thermal diffusion length and dynamic supercoiling.Secondly,based on the above-mentioned growth rate,it was applied in the runback icing model,and the relationship between the runback distance and the supercooling and water content was quantitatively constructed.When h_f0/?T is less than 5×10^-5m/K,rapid short-distance icing occurs;when h_f0/?T is greater than 2.5×10^-4m/K,long-distance runback icing occurs and the relative runback distance is 40m·s/kg.The relationship between the horn-ice angle and the distance was constructed by ice simulation.When the runback distance increased from 30 m·s/kg to40 m·s/kg,corresponding to h_f0/?T from 2.0×10^-4 m/K to 2.5×10^-4 m/K,the horn-ice angle increases nonlinearly around 10 degrees.At the same time,the corresponding aerodynamic performance decreases nonlinearly when the angle is greater than 10 degrees.The above analysis clarifies the synergistic variation of ice shape and aerodynamic response with environmental conditions.Thirdly,based on the ice-induced aerodynamic synergy,this paper chose two abnormal ice shape and used IDDES turbulence model to simulate the 3D flow field of 26°horn-ice and long-distance runback ridge ice under actual conditions,and quantitatively gives its aerodynamic hazard and stall angle.Then the macro-fluctuation phenomenon in the process of aerodynamic decline caused by the unsteady effect is mainly studied.The regular mode and shear-layer flapping mode that characterize the unsteady effect are respectively given,and the corresponding St is 0.56and 0.028.The above studies verify the correctness of the law of synergistic change and reveals the principle of aerodynamic decline and large fluctuations.Based on the above research,this paper has made some innovative progress in the following two points:Firstly,expanding the range of supercooling of ice growth rate law,explained the phenomenon of rapid icing and obtained the synergistic changer law of ice shape and aerodynamic characteristics with environmental conditions.Secondly,the aerodynamic response of abnormal icing under specific conditions is studied.The characteristics of the dominant unsteady mode of horn and ridge ice are given.