Separated Flow And Airfoil Icing Numerical Simulation Based On The Navier-stokes Equations At High Angles Of Attack

Separation flow will occur when aircrafts fly at high angle, the characteristics of Separation flow have an effect on aircraft performance. It is of importance in aircraft design to analyze this flow and aerodynamic characteristics by means of CFD.In order to investigate the effect of ice on the aerodynamic characteristics of the airfoil, ice accretion on the leading edge of the NACA0012 airfoil is predicted using Computational Fluid Dynamics in this paper. The ice accretion is considered a quasi-steady process in which the accretion is calculated layer by layer, assuming a constant flow field during the accretion of each new ice layer. The three basic steps are as follows: Firstly, the flow field is computed. Secondly, the droplet trajectory equation is solved in order to determinate the limiting droplet trajectories and local collection coefficient. Thirdly, a new iced shape is defined according to ice accretion model. When the ice grows to a determinate thickness, according to new shape, the flow field and the droplet trajectory equation are computed again, namely, the three steps above are iterated until the expected icing time is attained.According to the some aspects above, the major works of this paper are as follows:1. The flow field is calculated by solving the 2D compressible N-S equations. 2Dviscous grids are generated by solving the elliptic grid generation together with an algebraic method marching along the normal-to-wall direction. The 2D Euler program based on Jameson's central finite volume method is upgraded with modified artificial viscosity and time stepping schemes, etc. Euler program become N-S program by adding B-L model. Complex boundary conditions are treated simply and avoided repeat introduction by adopting "ghost" cells, at the same time, the computational efficiency is improved and the program's complexity is reduced, too. Finally, the 2D N-S program is extended to 3D.2. The separation flows of the ONERA M6 wing, slender body of missile and deltawing are simulated, the simulation capability of B-L model on large eddy is tested, the computational results agree well with experimental data.3. According to the Newton's second law, the droplet trajectory equation is established,the flow field calculated by N-S equation is regarded as the base of droplettrajectory equation solved. A 4-order Runge-Kutta method is used to solve the droplet trajectory equation in order to determine the droplet impingement zone. 4. The two ice accretion models corresponding rime and glaze are established. The results are as follows: the computational results of rime accretion model are the best agreement with computational results and experimental data found in the literature; the computational results of glaze accretion model agree well with computational results found in the literature, but both are different to the experimental data. The effect of the number of grid, liquid water content (LWC), median volumetric diameter(MVD) and ice layer time step on ultimate ice shape is analyzed, the aerodynamic characteristics of the iced airfoil is analyzed simply, too.