Prediction of aerodynamically induced fan blade vibration due to boundary layer ingestion

New aircraft concepts such as boundary layer ingestion (BLI) are essential to achieve a reduction of engine emissions and aircraft noise. The key-point of this concept is that the engine ingests and reaccelerate the boundary layer from the aircraft fuselage in order to increase propulsive efficiency. The investigation of the aerodynamic and aeroelastic interaction of the BLI and fan becomes necessary. For the calculation of the vibration response a process chain is established, starting by the calculation of the non uniform steady-state flow field and the resulting unsteady airloads using Harmonic Balance CFD-methods. Further the blade response is calculated with a Frequency Response Function-formulation in state space using the eigenfrequencies, eigenvectors and the aerodynamic damping of the system. Several BLI’s corresponding to different flight conditions and structural integration scenario of the engine were investigated and analysed for a wide range of rotational speed. Detailed forced response and fatigue analyses were performed for these point at peak efficiency. Resonance points with the first and second mode shape provoke significant peaks in the strain amplitudes and the inverse reserve factor (IRF). Beside that, resonance points with higher harmonics generate a relevant but not dominant contribution to fatigue.