Assessment of jet noise shielding prediction parameters

Abstract

Positioning aircraft engines on the rear of the fuselage above a U-shaped empennage is a concept configuration, which is expected to reduce the engine noise propagated towards the ground during take-off and approach. In order to assess the noise reduction benefits attainable from such a configuration, it is necessary to firstly develop appropriate acoustic evaluation tools. In this paper, a new methodology is presented, which uses a RANS solution input to model the complex jet flow as acoustic sources for use in shielding predictions. This methodology is employed as a sensitivity analysis tool in order to establish which parameters are important to consider in jet shielding predictions. Although, the predicted isolated jet directivity agrees well with far-field empirical values, the predicted levels of shielding are much larger than those observed in the available data. A preliminary investigation into the possible causes of this discrepancy indicates that the introduction of the shield adjacent to the jet results in the generation of new 'installation' sources, which limit the shielding achievable in practical applications.