Numerical modeling of flutter in a transonic fan

Abstract: Flutter is a self-feeding and potentially destructive vibration that can lead to devastating effects such as broken blades. Using accurate numerical models to predict flutter in the conception of an engine is essential to avoid huge waste of money. The software 2, using the elsA CFD package developed by the French Aerospace Lab, ONERA, is used to perform unsteady calculations and predict flutter margin. The current methodology does not systematically manage to reproduce the expected flutter pocket in transonic areas. The aim of the study is to investigate the impact of some parameters, such as boundary conditions and the position of the inlet and outlet plans of the mesh, on unsteady results. Results show that the current methodology, using conditions of injection at the inlet and an association of radial equilibrium and valve law boundary at the outlet, is inaccurate due to problem of reflecting waves that disturb the results. Using conditions of non-reflection at the inlet and the outlet seems more appropriate. Nevertheless, the new flutter margin using conditions of non-reflection does not permit to reproduce the flutter pocket either. New lines of investigation such as the impact of the density of the mesh or the time scheme may improve the numerical results.