An Analysis of the Aeroelastic Behaviour of a Typical Fan-Blade With Emphasis on the Flutter Mechanism

Aeroelasticity phenomena are characterised by the interaction of fluid and structural domains, whose describing equations are nonlinear. Classical prediction methods are generally based on treating the two domains separately while integrated (or coupled) approaches link them via boundary conditions throughout the solution phase. In turbomachinery environments, the aeroelasticity problem is further compounded by the fact that blades vibrate with a relative phase with respect to each other, the value of which is not necessarily known. Using a 3D thin-layer Reynolds-averaged Navier-Stokes solver and a 3D structural model, various coupled and uncoupled flutter analysis methods are compared with particular emphasis on inter-blade phase angle. A typical fan geometry, the NASA Rotor 67 blade, was chosen as the test case since steady-flow measurements are available for this particular structure. Two flow conditions, near peak-efficiency and near stall, were investigated for inter-blade phase angles of −90°, 0°, 90° & 180°. The performance of the uncoupled analysis with shape correction was first compared with that of the uncoupled multi-passage analysis. A coupled multi-passage analysis was performed next in order to highlight the importance of fluid/structure interaction. It was found that significant natural frequency shifts could exist between the structural and aeroelastic modes of the system, which suggests that coupled analyses may be more appropriate for such cases.