Prediction of Steady and Unsteady Aerodynamic Forces for Wings Using CFD Methods.

Abstract

In the following, theoretical flow procedures which occur in the transonic speed range of modern commercial aircraft are researched. One main point is the calculation of periodic motion-induced air forces in order to identify unwanted aeroelastic instabilities for an entire configuration as well as for individual components. The influence of the friction of viscous flow is ignored. The theoreticalresults of selected standard wings are compared with available measurements. The starting point of a calculation is the spatial three-dimensional Euler equations which are solved by an efficient upwind procedure in which time-dependent boundary conditions are observed. The initial values of a time-accurate calculation correspond with the solutions of a separate steady calculation. The transition to the stabilized oscilltion of the solution is dependent on reduced frequency as well as on amplitude. The upwind procedure is based on the complete Riemann solution in a closed form. In contrast to presently employed methods that are basedon approximate Riemann solutions or on flux splitting, the numerical error is dependent only on the local discretization and not on the local gradient of the solution. As a result, the numerical solution always correctly reflects the physical process of the inviscid flow. This allows for more extensive application, e.g. the determination ofthe shock-induced drag of a complex three-dimensional configuration.