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Session: Low/high order methods 1
Session starts: Wednesday 19 June, 13:30
Presentation starts: 13:30
Room: Room 1.3

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Cedric Liauzun (ONERA)
Christophe Blondeau (ONERA)

Abstract:
Several typical aeroelastic phenomena and instabilities, like flutter, induce periodic oscillations of the structure and of the aerodynamic forces. Numerical methods based on the harmonic balance technique or the Time Spectral Method (TSM) with a projection on the Fourier space has proven to be very efficient to predict the oscillatory phenomena by resolving the established regime without solving for the transient one. Such formulations lead however to critical numerical difficulties especially with a fine time sampling. A modular parallel TSM solver is developed in order to perform aeroelastic analyses and optimizations of wings. This solver is in charge of performing all the operations regarding the time discretization and the time resolution. An interface with the CFD elsA solver extracts all the needed information related to space discretization. Such architecture allows the adaptation of the TSM solver to any CFD codes (structured/unstructured), and most of all allows assessing and developing easily new resolution algorithms to improve the robustness and the computational efficiency. The structural deformations are taken into account in the TSM problem by an ALE formulation of the fluid equations. The time resolution of the TSM problem is carried out using an Approximate Newton Krylov method. Particular attention is paid for the investigation on the methods to solve the linear systems resulting from the ANK approach, especially on their preconditioning. An adjoint formulation of the TSM approach is also developed in order to perform aeroelastic optimizations with dynamic objective functions. The adjoint solver is actually aimed at replacing the low fidelity gust load computation based on DLM in an aeroelastic sizing and optimization process. This TSM solver is evaluated for inviscid flows in the cases of a 2D airfoil to which pitching motions are applied, of a 3D large aspect ratio wing (DLR-F25) subjected to harmonic oscillations which shape is a structural eigen mode one, and subjected to gust loads. A last case concerns the gust response of a 2D airfoil with plunge and twist degrees of freedom.