Prediction of Unsteady Aerodynamic Forces for Elastically Oscillating Wings Using CFD Methods.

Abstract

In the following, theoretical flow procedures which occur in the transonic speed range in modern commercial aircraft are researched. One main point is the calculation of preriodic motion-induced air forces in order to identify unwanted aerodynamic instabilities for an entire configuration as well as for individual components. A useful aerodynamic stability criterion can be derived from the power coefficient. The influence of the friction of viscous flow is ignored. The theoretical results of selected standard wings are compared with measurements. The starting point of the calculations is the spatial three-dimensional Euler equations which are solved by an efficient upwind procedure in which time-dependent boundary conditions are observed. The upwind procedure is based on the complete Riemann solution in a closed form. In contrast to presently employed methods based on approximate Reimann solutions or on flux splitting, the numerical error is dependent only on the local discretization and not on the local gradient of the solution. The initial values of a time-accuratecalculation correspond with the solutions of a separate steady calculation. The time-dependent grid deformation is taken into account virtually without restriction. This procedure is described in this paper.