Fan Inlet Mode Detection from Measurements of the Radiated Sound Field

Knowledge of the modal content of the sound field radiated from a t urbofan inlet is important for source characterisation and for helping to determine noise generation mechanisms in the engine. An inverse technique for determining the mode amplitudes at the duct outlet is proposed using pressure measurements on the Turbulence Control Screen. This paper discusses the feasibility of this inverse technique and details the important issues that need to be taken into account for robust and accurate inversion. Pressure measurements of broadband sound field generated by a lab-scale fan inlet are carr ied out. Results for the mode amplitudes computed from both external and in-duct sensor arrays are given.