Research Of Surface Roughness And Convective Heat Transfer On Airfoil Icing

When aircraft flies in clouds with super-cooled droplets, ice accretion will happen due to water impinging and freezing. The aircraft surface becomes uneven, which induces the emergence of surface roughness. The roughness elements caused by ice accretion w ill influence the flow field, move the transition position forward and enhance the convective heat transfer between the aircraft and the air flow. During the simulation process of aircraft icing, surface roughness and convective heat transfer have a great effect on the ice shape and amount. Thus, taking into account of the roughness elements and improving the current ice accretion model can improve the accuracy of the simulation result.The main content of this paper is: Firstly, the emergence and measurement of the surface roughness during ice accretion process is introduced, and the concept and influencing factors for the heat transfer coefficient is briefly stated. Then, the introduction of the numerical simulation procedure for aircraft icing is given, and two ice accretion models: the Messinger model and the model based on liquid water are presented in detail. Simulation results of each model are compared which concludes that different model is suitable for different ice accretion type, and they need to be combined in order to improve the calculation accuracy. After that, the equivalent sand grain model, the roughness calculation model based on surface geometry and liquid water behavior are introduced respectively. After considering the applicability of each model, a new multi- inf luencing-factors model is proposed. In the fourth chapter, two methods: the FLUENT software method and the boundary layer integral method for heat transfer coefficient calculation are explained and compared. For the first method, the parameters and settings which effect the calculation results are analyzed and the reason for not applicable for icing simulation is explained theoretically. And for another method, some improvements are implemented. In the fifth chapter, the new roughness model and the improved boundary layer integral method are both incorporated when establishing the improved ice accretion model. Several simulation cases are conducted on the NACA0012 airfoil under different icing conditions, the results are then compared with experimental ones in order to prove the validity and accuracy of the improved model. Finally in the last chapter, the research work carried in this paper is summarized which concludes that the newly proposed ice accretion model can improve the simulation accuracy and has guiding significance for the research and design of the anti/de-icing systems.