Acoustic Effects of Liner Damage on Zero-Splice Turbofan Intake Liners: Computational Study

Traditional installations of turbofan intake liners include acoustically “hard” axial splices between liner segments for ease of fabrication and assembly. The splices scatter energy from strong rotor-locked tones into adjacent azimuthal orders for which the liner is less effective, thereby degrading the liner performance. The significance of this “splice effect” has led to the adoption of “zero-splice” liners in recent turbofan nacelles. However, damage can occur to such liners in service, and the extent to which local liner repairs reduce the effectiveness of the zero-splice design then becomes an issue. In the current paper, the acoustic effect of damage and repair in a zero-splice liner is simulated numerically. The effects of the extent and the location of a hard patch, representing the liner damage and repair, on the overall performance of the liner are predicted. A close agreement is demonstrated with results from an asymptotic analytical model valid for small patch widths. An approximate method is also described to account for the effect of the nonlinear propagation on linear predictions of the liner performance when repairs are present.