Assessment of Conceptual Noise Reduction Devices for A Main Landing Gear using SNGR Method

Paper in proceeding, 2015

The noise-reduction efficiencies of three conceptual designs are explored for a main landing gear (MLG) mounted on a simplified fuselage body with a bay and gear door. The designs are a fairing attached on the strut, compression of the bay space as the gear is deployed, and acoustic liners installed in the interior downstream wall of the bay. The gear door is opened in order to investigate its reflection effect on the noise during the operation. The stochastic noise generation and radiation (SNGR) method coupled with the Reynolds-averaged Navier-Stokes (RANS) equations are used for the noise prediction. This approach has the advantage to speed up the computation of both the fluid flow and noise. The Cartesian immersed boundary method (IBM) that is employed for the RANS solver further shortens the period of the overall assessment process due to fast and automatic mesh generation. The present SNGR method integrates the Lighthill analogy and the boundary element method (BEM). The Lighthill analogy is used for the prediction of the noise produced by a synthetic turbulent field that is constructed with a stochastic model based on the time-averaged turbulence quantities obtained from the RANS solution. The BEM is applied to compute the surface-scattered noise. The current fairing design is found inefficient for the noise reduction. The strategy of reducing the bay depth is not functional as well. However, the liners are effective for absorption of the acoustic pressure on the surfaces. Moreover, the noise reflection effect of the gear door is clarified. Since the horizontally projected area of the door is not negligible, the noise reflected towards the ground is found significant in the high frequency range. The conclusion is that a gear door and the way of arranging it in the gear-deployed stage should be regarded as the important factors of the product design.