Unsteady aerodynamics and aeroacoustics of a fan rotor of a high-bypass ratio turbofan engine

Abstract

The purpose of this study is to predict the broadband noise generated by the fan rotor of a high bypass ratio turbofan engine. A numerical investigation of the unsteady aerodynamics of a fan rotor is described, with emphasis on acoustics. Two flight conditions are discussed: cruise and takeoff. For each case, three case studies are examined: namely, operating point, a choked point and a near surge point. It is found that the dominant broadband noise mechanisms are due to interaction of turbulence of the incoming flow with the engine casing and nose, interaction of the turbulent boundary layers on the rotor blades with their trailing edges and interaction of the rotating blade with the turbulence in the incoming flow. The most important noise source is the interaction of the turbulent boundary layers on the rotor blades with their trailing edges. Choked case exhibits the highest noise level as it has the maximum turbulent kinetic energy levels, maximum mass flow rate and thus maximum relative Mach number. Near-surge case has the lowest noise level except at the lower part of the suction side of the rotor where the reverse flow and vortices causes higher levels of noise.