Effect of Over-the-Rotor Liner on Fan Flutter Stability

Previously published literature has proved excellent performance of the over-the-rotor acoustic liner (OTRL) in noise reduction. This work investigates the impact of the OTRL on fan flutter stability in a subsonic duct using a three-dimensional coupled singularity method. The effects of the axial position and the acoustic impedance of the liner on the fan flutter stability are examined. Results show significant near-field coupling between the acoustic liner and the rotor, affecting the unsteady blade loading distributions and intensifying as the liner and the rotor overlap axially. The fan flutter stability shows clear sensitivity to the liner’s acoustic resistance, while its dependency on acoustic reactance appears more complex. An energy-based analysis shows that secondary unsteady loading induced by rotor–OTRL interaction may inverse the phase of the total unsteady loading, thus affecting the fan flutter stability.