Acoustic absorption of the over-the-rotor liner applied to a ducted fan

Abstract

The shortened intake length of the ultra-high bypass ratio engine leaves limited space for acoustic liner installation. The conventional intake liner has to extend to the proximity of the fan rotor to reach the same acoustic level, forming a so-called over-the-rotor (OTR) liner. Large eddy simulation method is used in this paper to analyze the acoustic absorption of the OTR liner. The results show that the dissipated energy of OTR liner orifices varies along the duct axial direction. The orifices close to the blade leading edge have the highest velocity and thereby dissipate the most energy. The magnitude and pattern of orifice velocity are different distinctly at the upstream and downstream of the rotor affected by the pressure distribution inside the duct as well as the blade surface. The time delay of orifice flow along the circumferential direction indicates that the motion of fluid inside of the orifice is primarily driven by the hydrodynamic pressure perturbance of the passing rotor. The OTR liner exhibits more complicated acoustic absorption characteristics than conventional intake liner so further investigation is necessary to understand the underlying mechanisms.