Attenuation of FJ44 Turbofan Engine Noise with a Foam-Metal Liner Installed Over-the-Rotor

A Williams International FJ44-3A 3000-lb thrust class turbofan engine was used as a demonstrator for a Foam-Metal Liner (FML) installed in close proximity to the fan. Two FML designs were tested and compared to the hardwall baseline. Traditional single degree-of-freedom liner designs were also evaluated to provide a comparison. Farfield acoustic levels and limited engine performance results are presented in this paper. The results show that the FML achieved up to 5 dB Acoustic Power Level (PWL) overall attenuation in the forward quadrant, equivalent to the traditional liner design. An earlier report presented the test set-up and conditions. Nomenclature FML ςFoam-Metal Liner OTR ςOver-the-Rotor HW1 original hardwall flow path HW2 modified hardwall flow path A1 Target FML design (80 ppi/in.; 8% density) A1t FML w/forward 1/2-section taped A2 Target FML design (40 ppi/in.; 8% density) SDOF1 Single degree-of-freedom liner (designed for BPF at100% N1c) o SDOF2 Single degree-of-freedom liner (designed for BPF at 75% N1c) PWL Acoustic Power Level N1c Corrected Fan Speed BPF Blade Passing Frequency acoustic impedance