A computational study of the effects of liner damage on zero-splice turbofan intake liners

Traditional installations of turbofan intake liners have acoustically ‘hard’ axial splices between liner segments for ease of fabrication and assembly. The splices scatter energy from the rotor-locked tones into adjacent azimuthal orders for which the liner is less eective, thereby degrading the liner performance. The signicance of this ‘splice eect’ has led to the adoption of ‘zero-splice’ liners in many current turbofan engines. However, damage can occur to such liners in service. The extent to which local impedance changes due to liner repairs reduce the eectiveness of the zero-splice design then becomes an issue when determining how much damage is acceptable before noise certication levels are compromised. In the current paper, the acoustic eect of damage in a zero-splice liner is simulated by using a computational model. The eects of the extent and the location of the damage on the overall performance of the liner is assessed. The computed results are also compared to an asymptotic analytical model. Finally, a methodology is described to model non-linear propagation eects in an approximate way within the linear predictions.