Analytical prediction of boundary layer ingestion noise for an integrated turbofan

Abstract

A parametric study based on the analytical predictions of tonal and broadband noise for a generic turbulent boundary layer interacting with the rotor of an ultra high bypass ratio fan is presented. The approach and take-off conditions are considered. To classify the importance of ingestion noise, the rotor-stator interaction noise of the fan stage is also evaluated analytically based on computational fluid dynamic simulations. The implemented analytical boundary layer model provides the axial mean velocity profile and also the axial and transversal turbulent quantities. This allows to consider the turbulence within the boundary layer as anisotropic. The acoustic response of the rotor blades is predicted by using a modified theory for the acoustic radiation from an airfoil. The predicted tonal sound power levels are similar for the ingestion noise and the rotor-stator wake interaction noise at take-off conditions. For approach conditions the tonal boundary layer interaction noise is dominated by the rotor-stator wake interaction noise. The influence of the boundary layer thickness and the a shape factor, linked to the axial pressure gradient, on tonal noise is discussed. Concerning broadband noise the results indicate that the boundary layer interaction noise has the potential to dominate the low to mid frequency range compared to rotor-stator interaction noise. The predicted power spectral density levels show that the ingestion noise increases with boundary layer thickness and shape factor.