Study On Flow And Heat Transfer Of Runback Water On Anti-Icing Surface

Ice accretion on aircraft and aero-engine usually causes many problems of the flight safety. Generally, the reason of ice accretion is that the supercooled water droplets in the cloud impinge on aircraft surfaces. These water droplets in the cloud always retain the metastable state and the temperature is below the freezing point. A number of studies show that, ice accretion on aircraft surfaces have a considerable effect on aerodynamic configuration of aircraft and its handing and stability characteristics. Moreover, it may causes serious air crash. According to the airworthiness regulation, the anti-icing or de-icing systems are widely applied to protect aircrafts or aero-engines from icing.Nowadays, the thermal anti-icing systems are the most widely used in the commercial aircraft. The heat source of these systems is the hot air from the engine compressor, which could maintain the surface temperature above 0oC and avoid ice accretion. A layer of water film will form on the anti-icing surfaces if the heating energy of the anti-icing systems is not enough to evaporate all of the water impinging on the surface and run back on the surfaces due to the aerodynamic forces. The flow and heat transfer of the runback water have a significant influence on the determination of the required heating energy and area. Therefore, considering the effect of the water film on the anti-icing surfaces has important theoretical significance and practical value in engineering.This paper mainly revolves around the effect of water film flow to analysis the mechanism of the flow and heat transfer on anti-icing surfaces. The main contents of this paper are as following:First of all, a brief summary of the previous work is presented, including the basic conceptions and the research methods in this research field. On this basis, the flow field, water droplets trajectories and local collection efficiency are all computed by using ANASYS Fluent commercial software, the results of which are prerequisites for the study of the water film flow and heat transfer on the anti-icing system.Secondly, a mathematical model for the flow and heat transfer on the anti-icing surfaces is developed based on the interaction mechanism of the water film and air boundary layer. The model considers the driven effect of aerodynamic shear force, the evaporation and convection on the film surface. Both of the air flow boundary and water film flow are subjected to mass, momentum and energy conservation.Thirdly, a mathematical model of water flow evolution is presented and is used to predict the shape of the rivulets on anti-icing surface when the water film breaks up into individual rivulets. The validation of the model is carried out by the comparison between the computation of the model and the measurement of the airfoil from the reference.Finally, based on the mathematical models for the flow and heat transfer as well as the breakup of the water film, the effect of the different anti-icing conditions and free stream parameters are all analyzed in this paper.The analysis methods and the computation results in this paper can provide references for the design of anti-icing systems to a great degree. Due to the complexity of the physical mechanism and the diversity of the relevant subjects in the water flow phenomenon, the models presented above may lead to further developments.