1. Introduction

Two and three dimensional flutter problems simulation is a challenging task and is interesting from both industrial and academical aspects. Usually, structure design concerns the structural characteristics of the model, something which is usually performed without taking into account the possible flow unsteadiness. At this step, the design accounts often at best for mean flow loads and tries to avoid resonance phenomena for a few flow eigenmodes corresponding to the lowest structural modes where the eigen-analysis is done for each model separately. On the other hand, aerodynamical shape optimization is usually performed for given structural characteristics after adding geometrical constraints on local thickness for instance to guarantee a realistic final shape from structural point of view. Current efforts concern the realization of this task in a MDO (multi-disciplinary) context for steady configurations. In both cases, it is therefore reasonable for the flow to stay in the validity domain of these optimizations, which means as much as possible steady or close to it. We are therefore interested to control unsteadiness which might appear in a fluid/structure system even in cruise condition. One easy way to perform this task is by perturbating the inflow incidence using a real time flap position perturbation prescribed by a fast gradient based minimization algorithm. The sensitivity evaluation and the minimisation tool have therefore to be fast enough. In that sense, different control laws are obtained using different minimization algorithms and the control is in...