Study On The Computational Methods Of Flow And Heat Transfer During In-Flight Anti-Icing And Icing

In-flight icing is a serious threat to flight safety.When flying under icing conditions,it may occur on the aircraft upwind surfaces if no appropriate anti-icing actions are taken.As airline accidents caused by in-flight icing have still been occurring in recent years,wide attentions are still paid on this phenomenon and anti-icing problems.As an important way to study in-flight icing and anti-icing problems,numerical simulation technologies are widely applied and developed in these years.Considering the current situation and the trend of anti-icing calculation researches,the commercial CFD software ANSYS Fluent is chosen as the development platform in this thesis and the studies focusing on the calculation methods of anti-icing and icing phenomena are taken as follows:Firstly,based on the extended development tool supplied by ANSYS Fluent,calculation methods on water droplet impingement characteristics are studied in detail.Both Lagrangian approach and Eulerian approach are realized in ANSYS Fluent.When droplet impingement characteristics is calculated in Lagrangian frame,droplets' trajectories are obtained by Fluent Discrete Phase Model(DPM)and calculation of local collection efficiency on the surface are implemented by a statistical approach.This method makes it possible to calculate the local collection efficiency on the complex three dimensional surfaces easily.When calculated in Eulerian frame,the governing equations of droplet phase are solved in Fluent User Defined Scalar frame(UDS),which makes it possible to obtain the local collection efficiency in either reference frame supported by Fluent.Based on the methods above,local collection efficiency on both two dimensional and three dimensional airfoil surfaces are solved.The results of current work meet well with the data reported in the reference paper.Meanwhile,extension researches on calculation methods are conducted to obtain the droplet impingement characteristics under supercooled large droplet(SLD)conditions and local collection efficiency in two dimensional axisymmetric reference frame by Lagrangian approach under Fluent-based environment.Moreover,a method combined Lagrangian and Eulerian approach is developed in this thesis,which is proved to be effective to improve the stability and efficiency of Eulerian approach.Secondly,the computational method to solve the fluid flow and heat transfer on the component surfaces under anti-icing conditions is studied.Based on the classical Messinger Model in anti-icing analysis,mass conservation and energy conservation of water film flow on the component surfaces are analyzed.The computational method to gain the water film flow mass flux on the surface as well as the distribution strategy on the runback water flow mass flux for unstructured surface mesh is developed.On the calculation of surface temperature under anti-icing conditions,the heat fluxes caused by water impingement and runback are added into the energy equation by Fluent User Defined Functions(UDF).By applying the coupled heat transfer boundaries,the heat transfer between anti-icing hot air and the solid wall as well as the solid wall and the cold air can be solve automatically under anti-icing conditions so that the surface temperature under anti-icing conditions can be obtained.Based on the method above,the temperature profiles on the anti-icing surfaces of stationary aero engine components are calculated and the results are validated by comparing with the test data.In addition,analysis are also made on the water flow mass flux as well as the heat flux on the anti-icing surfaces within different runs.Thirdly,the calculation method on the shape of the rivulet after water film break up is studied.To gain the thickness of the water film at the break up position,the mass conservation and the momentum conservation of the water film flow is analyzed and calculated.The film is generally very thin so that linear assumption is valid to be applied in this calculation.In order to gain the thickness and the width of the rivulet,a solution strategy is developed based on the mass conservation as well as the energy conservation of water film flow and rivulet flow,in which the rivulet cross section shape is assumed to be a part of a circle.By comparing the calculation result to the reported data,the current method could predict the water rivulet shape within certain tolerance.Based on the method above,the rivulet shapes on an anti-icing aero engine strut are studied under different surface temperatures as well as impinged water droplets' MVDs and the effects of these factors are analyzed.Finally,the prediction method of ice shapes is studied.Based on the mass conservation and energy conservation on the icing surface,thermal dynamic model on the icing surface is studied and the calculation method on ice accretion for unstructured surface mesh is developed.To obtain the ice shapes,the surface node update algorithm is developed so that the computational domain after icing can be automatic updated with the help of the Dynamic Mesh(DM)technology supported by ANSYS Fluent,which makes it possible to realize the multi-step icing prediction.The current method is validated by calculating the cases of the classical experimental and numerical data.Moreover,icing processes on aero engine rotating components are studied based on the method above and the icing regularity on these components are also analyzed.