Investigation On Water Droplet Movement Characteristic And Icing Region Prediction For High Bypass Ratio Turbofan Rotating Fan

Ice may accumulate on the aircraft when the aircraft passes through an environment containing a large amount of supercooled water droplets,which is called aircraft icing.Recent research found that icing on aircraft engines was far more harmful than on other upwind components of the aircraft.Ice accumulated in the flow path of the engine will reduce the thrust,degrade the aerodynamic characteristic of the engine flow path,reduce the efficiency of inlet duct and may cause hazard such as engine stall and surge,which seriously affects the safety of the aircraft.Therefore,it is of great significance to carry out research on the icing process of aero-engine inlet components.Ice will also accumulate on the fan blades of high bypass-ratio turbofan engine when the aircraft passes through clouds containing supercooled water droplets.However,due to the complex flow field around the fan blade and its high tip speed,it is difficult to accurately predict the impact region,impingement mass flow rate and icing shape of fan blade,which is very challenging.Besides,the research of the water impingement characteristic and icing phenomenon of turbofan engine fan blades has not been extensively conducted in recent years.Therefore,it is necessary and meaningful to investigate the impingement characteristics of water droplets on turbofan fan blades and the possible icing process under icing conditions.Choosing the NASA transonic fan Rotor67 as the computational model and the commercial CFD software as the simulation platform,the flow field of the three dimensional and quasi three dimensional model were completed in this thesis.On the basis of quasi 3D and 3D flow field,the governing equations of water droplet phase established both in absolute and relative reference frame were solved by Eulerian approach numerically by means of embedding UDF codes,so as to investigate the droplet motion in fan blade passage.The results show that the collection efficiency of quasi 3D and 3D models are consistent.The droplet governing equations established in absolute reference frame can better reflect the motion of supercooled water droplets in the rotating fan blade passage,and the impact region and impingement rate on blade surface are more reasonable.The impact of the shock wave at the tip of the fan blade on the numerical solution of the droplet phase was also studied in this thesis.And the distributions of droplet volume fraction and relative velocity field were also analyzed and they show reasonable agreement with the experimental results.In addition,after considering the heat transfer between droplets and air and the heat transfer caused by water droplet evaporation,the droplet temperature variation along flow direction in fan blade passage was studied and the impingement temperature of the droplets was obtained.Furthermore,in view of the characteristics of fan flow field simulation,a method used to calculate the evaporation rate on fan blade surface was proposed and the net impingement mass flow rate on the blade surface was studied.Finally,combining with the impingement region and the temperature distribution of water droplets,a method was proposed to predict the possible icing region on the fan blade and the initial icing rate and icing shape on blade was predicted.In addition,the influence of pressure gradient force on the droplet motion and collection efficiency was also studied.A method to correct the meteorological conditions of fan downstream components of turbofan engines and a fast method to estimate the maximum collection efficiency of the leading edge of rotating components were proposed based on the numerical simulation result.The method established in this thesis can provide guidance for the research on fan blade icing of turbofan aero-engine,and lay foundation for further research on fan blade icing in the future.