Transonic Unsteady Aerodynamics And Flutter Computations For Complex Assemblies

In the present thesis, based on unsteady Euler and N-S equations, computational methods of unsteady aerodynamic forces and transonic flutter are studied in detail for complex assemblies.Multiblock grids with a reasonable topology are adopted for complex configurations. Both algebraic method and optimal elliptic partial differential equations are used to generate boundary grids of blocks, and then a simplified 3-D approach is developed for spatial grid generation. Dynamic grids are generated by the use of a rapid deforming technique with a limiter designed to prevent grids from overlapping near walls. Cases of grid generation show the practicality and efficiency of current static and dynamic multiblock method for complex configurations.The finite volume method and dual time-stepping approach is used to solve unsteady Euler and N-S equations. Baldwin-Lomax algebraic, Spalart-Allmaras One-Equation and SST Two-Equation turbulence model are respectively employed to the simulations of turbulent flows. The wall function approach is applied to model the near-wall region with comparatively sparse grids near walls. DES model is used to simulate the unsteady massively separated flows. For the interpolations of conservative variables on discontinuous interfaces, a convenient and effective rezoning method is developed to accurately simulate the steady and unsteady flows around a wing with control surfaces. Many means, either improving accuracy or accelerating convergence, are reasonably applied to achieve an integrated numerical method for unsteady Euler and N-S equations.Structural mode interpolations are fulfilled by the use of surface spline method. Confusions on dimensional matching between structural and aerodynamic equations, as well as between computational model and real aircraft, are made clear by dimensional analyses. Then unsteady Euler or N-S equations coupled with structural equations of motion are solved in the time domain. As a result, an integrated time-domain method for static aeroelasticity and flutter is obtained.Due to mass dissimilarity existed in flutter calculations of compressible flows, methods of variable mass and variable stiffness are developed to obtain a dynamic pressure of flutter, which meets the rule of mass similarity. Synthetical considerations on the variation trends of dynamic pressure of flutter varying with mass and stiffness multiples confirm a practicable dynamic pressure of transonic flutter. For the first time, idea of stiffness margin is put forward for compressible flows to offer a new way to analyze the flutter margin quantitatively.A combination of time-domain flutter calculations and method of variable stiffness leads to a flutter calculation method for different Mach numbers in the whole airspace. Finally, a comparatively self-contained software platform for subsonic, transonic and supersonic flutter analyses and calculations of complex assemblies is constructed, which has succeeded in solving the key problems of aeroelasticity for some kinds of complex assembly.