Comparative Assessment of Aircraft System Noise Simulation

Kurzfassung

The Aircraft Noise Working Group (ANSWr) was established by DLR, ONERA, and NASA to compare simulation tools, establish guidelines for noise prediction, and to assess uncertainties associated with the simulation. To accomplish these goals, a benchmark problem was initiated by the group. The benchmark setup is documented and initial results for a reference and a low-noise vehicle are discussed. The reference aircraft is a conventional tube-and-wing configuration with the engines installed under the wings. The low-noise variant features a high wing concept with engines mounted above the wing and fuselage junction. All aircraft noise simulations are performed for departure and approach conditions, and the results obtained with three different system noise prediction tools are compared. For the reference aircraft, the overall agreement is good among the three predictions. Peak noise levels agree within 3-4 dB. Fan and jet component predictions are generally very similar, although there can be differences of up to 7 dB in some fan tone levels. The prediction of airframe components shows the most disagreement among the three methods, with some differences of 6 dB for the major components and greater differences at high frequencies. There can also be differences in the frequency of the peak level and in the rank order of the airframe components. At the total airframe noise level, the differences are reduced to no more than 3-4 dB. While there is general agreement in shape characteristics of predicted ground noise isocontours, the differences among the three methods can result in more significant disagreement in the sizes of the isocontours. For the low-noise vehicle the prediction result is greatly dependent on the acoustic shielding of the engines by the airframe. Consequently, the comparison of the computed results focuses on the acoustic shielding calculations, as well as on the noise source components. Remarkably, all three prediction methods show good agreement with discrepancies typically lower than 4 dB for overall aircraft noise metrics such as peak noise levels. However, at forward and aft angles, the aircraft system noise predicted can begin to show much larger differences, up to 5-10 dB. Many of the differences at large angles can be attributed to the shielding predictions but can also be due to some significant differences among the three predictions of the airframe noise sources.