Computation of Noise Radiation from Fan Inlet and Aft Ducts

Abstract

This paper examines turbofan noise radiation characteristics of both the inlet and the aft exhaust ducts using solutions obtained from a finite element code. The far-field principal lobe peak angle variations with mode cutoff ratio, duct Mach number, and external flow Mach number are examined. The predicted far-field principal lobe peak angle variations compare very well with the available analytical results. It is found that the principal lobe peak angle of the inlet radiation is insensitive to the duct and external flow Mach numbers. In the case of the aft duct, an increase in duct Mach number moves the principal lobe away from the aft duct axis, whereas an increase in external flow Mach number moves the principal lobe toward the aft axis. The solutions (for both inlet and exhaust duct radiation) also show that the far-field radiation principal lobe peak angle is only a function of cutoff ratio and nearly independent of the mode number. The ability of the code to handle ducts with acoustic treatments is also demonstrated.