Acoustic Shielding of a Tapered Wing

Aircraft propulsion system noise can be a large contributor to ground level noise. Mounting the propulsor above the wing can reduce ground level noise below the vehicle. The level of acoustic shielding is dependent on wing planform dimensions and vehicle shape. Two different modeling approaches to predict noise shielding by tapered wings were investigated for use in an automated aircraft system modeling framework. The first approach uses the commercial code Virtual Lab (BEM, FEM, and Ray acoustics methods), and the second is the Maggi-Rubinowicz diffraction potential solution to the Kirchhoff Integral. Results from Virtual Lab were compared to two experimental results found in literature. Good agreement between Virtual Lab and experiment were obtained using the FEM. Acoustic shielding by tapered wings was calculated using FEM for the case of a single monopole noise source mounted on center just above the wing and compared to the Maggi-Rubinowicz diffraction potential method. Model development, analysis, and post processing were automated for both approaches so that they could be used as part of an aircraft system modeling framework. The FEM in Virtual Lab offers higher fidelity but higher computational cost, while the Maggi-Rubinowicz diffraction potential method is relatively lower fidelity since it is limited to use in diffraction problems with relatively simple geometry, and higher frequencies. A difference in shielding of several dB between the Maggi-Rubinowicz diffraction potential method compared with the FEM solution was noted, however, the diffraction potential method captures the correct trends in shielding and has much faster computational speed compared to FEM, which is beneficial for automated vehicle design routines.