A method for generating three-dimensional mixed element type unstructured grids and its application for viscous flow simulations by solving the Navier-Stokes equations are presented.Pirzadeh's advancing-layer method is modified to generate high quality mixed prismatic/pyramid/tetrahedral element type unstructured grids in boundary-layer region,and the traditional advancing-front method is used to construct isotropic tetrahedral grids in the residual flow region.Three-dimensional Navier-Stokes equations are solved by using a cell-centered finite-volume method.A new local time stepping method has been developed to eliminate the adverse influence of grid quality on solve stability and convergence speed.Viscous flow problems around the ONERA M6 wing and DLR-F4 wing-body configuration are simulated to verify the correctness and practicability of the methods presented.

An analysis method of the airfoil flutter system with nonlinear structure at transonic speeds is presented. The unsteady aerodynamic forces are calculated by Navier-Stokes equations. The time histories of structure responses of airfoil are solved by coupling the Navier-Stokes equations and flutter equations. The systems with gap stiffness, cubic type stiffness and cubic structure damping are investigated. The calculated results show that the influence of the structure nonlinearity on flutter speed is sensitive. Due to both the structure and aerodynamic nonlinearity in the flutter system, the oscillation characterstics become very complex.

The 2-D time-dependent compressible Navier-Stokes equations are adopted as the governing equations. The unsteady lift coefficients of airfoil are calculated by Navier-Stokes equations with the implicit LU-NND algorithm, Baldwin-Lomax turbulent model and C-type grids. The fluctuating values of lift coefficient are increased with the enlargement of incidence and Mach number. The buffet onset boundary is defined as the beginning point where the fluctuating values of aerodynamic coefficients are increased suddenly. The fluctuating values of aerodynamic coefficients expresses the buffet strength. The buffet characteristics of supercritical airfoil DFVLR-R2 and airfoil NACA0012 are investigated. The calculating results show that:in the design Mach number range of supercritical airfoil, there are larger buffet onset incidence and less buffet loads. When Mach number is larger than the design Mach number, the buffet onset incidence of supercritical airfoil decreases quickly and there are rather large buffet loads. In the convention airfoil NACA 0012, there are much less buffet onset incidence, larger buffet loads and separated range.

A method for generating three-dimensional unstructured viscous grids automatically is presented. High-aspect-ratio and anisotropic tetrahedral grid cells are constructed in viscous dominated flow regions by advancing-layers method (ALM).When the height of viscous grids reaches the requirement,the conventional advancing-front method (AFM)will generate isotropic grids to fill the remained flow regions.By the control of stretched function and background information,the transition from grids generated by ALM to isotropic grids generated by AFM becomes smooth and gradual.The unstructured viscous grids of M6 wing and the simple flow results of corresponding Navier-Stokes solution based on the present grid are also provided.

A dual-time scheme is used to solve the unsteady compressible Navier-Stokes equations to obtain the needed airload.The model structural equations of motions are computed simultaneously using the Runge-Kutta method to calculate the aeroelastic static deformations and responses of wings in the time-domain.The O-H type grid around the deforming wings is generated using the improved transfinite interpolation method so that grid generation in each time-step is not too time-consuming.The numerical results show the transonic flutter speed drop and nonlinear characteristics.