Nonlinear Aeroelastic Simulations and Stability Analysis of a Highly Flexible Wing

Abstract

The goal of this thesis is the extension of the existing simulation tools at DLR and their application for aeroelastic modelling and validation of the highly flexible Pazy wing wind tunnel model. As large deformations are expected due to the wing's special design, the simulations should in particular account for the nonlinear behaviour of force-structure interaction (follower force problem) and geometric nonlinearities. Therefore, an aeroelastic solver developed at DLR is used, coupling a geometrically nonlinear vortex lattice method with the nonlinear static solution sequence SOL400 of the finite element solver Nastran. Besides determining steady aeroelastic equilibrium points by the means of this solver, the aeroelastic stability of the wing in terms of flutter is also to be investigated. Since common flutter speed prediction methods are only applicable to rigid structures undergoing small deformations, an important part of this thesis is the development of a method for stability analysis of highly flexible wings. Therefore, the whole aeroelastic system is linearised at static equilibrium points with large deformations using linear discrete-time state-space models. The proposed method is then verificated using nonlinear simulation tools in the time domain. Subsequently, static coupling simulations are performed for a range of onflow velocities and angles of attack. Since the structural properties are affected by the deformation of the wing, the change of mode shapes and eigenvalues is evaluated afterwards as a function of the deformation. Finally, the aeroelastic stability of the wing is determined by means of the proposed method. The results are validated with reference results obtained from the Nastran aeroelastic flutter analysis solver SOL145 and with data computed by an approach similar to the method developed in this thesis.