Turbulence interaction noise from a rectilinear cascade of airfoils and effects of porous material inclusions

Abstract

The broadband noise radiated by turbulent fan wakes interacting with the outlet guide vanes is one of the major broadband noise components of turbofan engines. In this paper, this broadband turbulence interaction noise is studied experimentally in an anechoic wind tunnel on a simplified configuration consisting in a rectilinear cascade of airfoils impinged by a turbulent flow generated by a turbulence grid. The cascade is made of 7 loaded airfoils with an adjustable incidence angle and the upstream flow velocities investigated are up to a Mach number of 0.53. The noise radiated by the cascade is evaluated using a circular array of microphones located in free-field downstream of the cascade, and also using a linear array of microphones flush mounted in the duct upstream of the cascade. A concept of airfoil with inclusions of porous material has been designed based on previous work and manufactured to be tested on this rectilinear cascade configuration. The results of the measurements performed with this airfoil concept are compared to the results of the fully rigid reference airfoil.