Investigation On The Numerical Simulation Methods Of Ice Accretion And Anti-Icing On The Aircraft Surface

Aircraft icing is a key aviation safety issue,as ice accretion on the aircraft surface might cause performance degradation,which would bring great threat to flight safety.With the development of numerical simulation methods and large-scale parallel computational techniques,numerical simulations of aircraft icing and anti-icing have been applied in the early stages of the aircraft design and the anti/de-icing system design.This thesis conducts researches on the numerical simulations of aircraft icing and anti-icing with finite volume method,which involves the impact characteristics of supercooled droplets,complex mass and heat transfer,and the runback flow on the icing and anti-icing surface.A numerical simulation tool for aircraft icing and anti-icing is constructed,the unsteady heat transfer process in the growing ice layer is directly solved based on the unsteady Stefan problem in order to improve the accuracy of the predicted ice shapes and robustness,a film flow model is proposed based on the Lubrication theory and the finite volume method,and an anti-icing model is developed to simulate the heat and mass transfer on the fully evaporative and running-wet anti-icing surface.The main contributions of this work are summarized as follows:(1)The roughness extension for the turbulence model is improved,and a numerical simulation method for the turbulence flow over rough iced surface is developed.To account for the effect of wall roughness,the wall-value of ω of the roughness extension for shear stress transport k-ω two equations turbulence model is modified to increase the near wall eddy viscosity and the total wall shear stress.To improve the computational efficiency,the convective heat transfer coefficient is solved based on the CFD results and the near-wall temperature gradient.The predicted velocity shift matches well with theoretical results when the flow is in transitional regime compared with the roughness extension by Knopp,meanwhile,the skin friction coefficient,the Stanton number and the lift coefficient agree better with experiments.(2)Numerical simulation methods for the three-dimensional droplet flow with ice accretion are developed,and a numerical simulation platform for airfract icing is constructed.Eulerian approach is adopted to solve the impact characteristics of supercooled droplets,and the effects of the rebound and splash of the supercooled large droplets are considered by correcting the local water collection efficiency.Langmuir-D distribution of droplet diameters is utilized to improve the prediction accuracy of the local water collection efficiency near the impingement limit.The ice shape is parameterized by the nonuniform rational B-splines(NURBS),and the grid points on the iced region are refined according to the curvature in order to capture the geometrical features of the ice shape.The influences of the medium volume diameter(MVD)on the impact characteristics of the droplets are investigated,and conclusions are made that smaller MVDs represents better tracing accuracy and smaller impingement range.(3)A three-dimensional aircraft ice accretion model based on the numerical solution of the unsteady Stefan problem is proposed,an efficient grid generation strategy for ice accretion is developed,and the accuracy of the predicted ice shapes is improved.The heat conduction within the ice layer is considered as an unsteady process for both rime and glaze ice situation,the temperature distribution in the growing ice layer is numerically solved by Variable Space Grid(VSG)method.Hence the amount of the latent heat of solidification conducting to the wall through the ice layer is directly computed,which solves the issue in the overprediction of the icing rate predicted by the classical Myers’ ice accretion model.A hierarchical overset grid strategy is applied and a thin grid around the iced surface is regenerated in order to ease the grid generation on complex icing configurations,improve the grid quality and capture the complex flow characteristics near the ice horn.Simulations on the two-dimensional airfoil and the three-dimensional wing are conducted and the availability of the ice accretion model is verified.(4)A three-dimensional film flow model for the runback water on the iced surface is proposed,and the numerical method for the governing equations of the film flow is developed.The film flow governing equations in terms of the film thickness and the film velocity are derived based on the Lubrication theory,finite volume method and the Gauss divergence theorem.The film velocity is expressed explicitly as a function of the air shear,gravity,the pressure gradient and the film thickness by analyzing the characteristic of the film flow,which simplifies the computation of the film thickness.The first layer structured grid cell is selected as the computational grid for the film flow,the depth-averaged velocity of the film is stored in Cartesian coordinates,and the governing equations are discretized by finite volume method.With these approaches,the metric tensors of coordinate transformation are avoided and the difficulty of the numerical simulation of the film flow is reduced.Numerical simulations of the runback water flow and ice accretion on the two-dimensional airfoil and the three-dimensional wing are performed.Results show that the characteristics of the glaze ice and the film flow are well simulated with current film flow model and numerical simulation method.(5)A computational model and a numerical simulation method are developed based on the iced surface film flow model,and the surface temperature characteristics are evaluated for fully evaporative and running-wet anti-icing situations.The mathematical models for fully evaporative and running-wet anti-icing situations are established according to the mass and energy conservations.In terms of the running-wet anti-icing model,the effect of mass transfer of the water film on the heat transfer is taken into consideration,and the unsteady and convective terms are reserved.Numerical simulations of the fully evaporative and running-wet anti-icing process on the NACA0012 airfoil are performed to predict the temperature on the anti-icing surface and verify the validity and reliability of the anti-icing model.Results show that,for fully evaporative anti-icing situation,high anti-icing power is required to evaporate all the impinging supercooled droplets,while for the running-wet anti-icing situation,when the anti-icing heat power is insufficient,the runback water might flow onto unprotective zone and freeze,resulting in ice ridge.