The Advection Boundary Law in presence of mean-flow and spinning modes

Abstract

In the attempt to reduce fuel consumption, a new generation of Ultra-High-By-Pass-Ratio (UHBR) turbofans have been introduced in the aeronautic industry which are structurally noisier especially at lower frequencies, because of their larger diameter, lower number of blades and rotational speed. Moreover, they present a shorter nacelle, leaving less available space for acoustic treatments. For this reason, innovation in the liner technology is highly demanded. In this contribution, we analyse the performances of an electroacoustic liner, made up of microphones (sensors) and small loudspeakers (actuators). Such array of electroacoustic resonators can feature an interesting boundary operator, called Advection Boundary Law. Such boundary law has been analysed in grazing-incident acoustic fields without air-flow and in case of plane waves. Here, we adapt such boundary condition to attenuate spinning modes. Numerical simulations in case of spinning-modes, shows the potentiality and the passivity issues of such innovative boundary law. Finally, a reproduction of a turbofan engine (scale 1:3) accomplishing real-life rotational speeds, allows to assess the performances of the Advection Boundary Law in presence of mean-flow and spinning-modes.