Aircraft System Noise Assessment of the NASA D8 Subsonic Transport Concept

Abstract

A vehicle-level noise assessment has been performed for the NASA D8 concept aircraft (ND8) in the NASA Advanced Air Transport Technology Project portfolio. The NASA research-level Aircraft NOise Prediction Program (ANOPP-Research) was used to predict the noise from each source component on the ND8 to build up a noise estimate for the full aircraft. The propulsion airframe aeroacoustic (PAA) effects of the ND8, namely boundary layer ingestion (BLI) with its influence on fan noise, and the noise shielding, reflection, and diffraction mechanisms of the unconventional airframe, were empirically modeled using experimental data. Noise reduction technologies appropriate to the 2025-2035 time frame were included in this study. Including all technologies and PAA effects, the ND8 is predicted to have a cumulative margin to the Stage 4 certification metric of only 7.4 EPNdB. Boundary layer ingestion is predicted to have a detrimental impact on cumulative noise levels on the order of 15 EPNdB. Fan noise is seen to be the primary noise source at all three certification points, even if the BLI noise impact could be entirely suppressed. The impact of engine noise shielding by the airframe is limited by a lack of aft shielding and the presence of horizontal tail reflections in the aft direction. The physical constraint on engine size by the pi-tail is seen as a potential barrier to engine noise reduction through the corresponding limitation on fan bypass ratio. Mildly reduced climb performance (compared to similar reference aircraft) does not provide any benefit through increased noise propagation distance. If the boundary layer ingestion noise penalty could be suppressed such that BLI would have no effect on noise, the cumulative margin to Stage 4 would increase to 22.4 EPNdB, still below the NASA Mid Term goal of 32-42 EPNdB.

Recent Advances in Boundary Layer Ingestion Technology of Evolving Powertrain Systems

“…Finally, Clark et al [80,81] published two studies focused on the noise assessment of the D8 concept. In both studies, the authors used the NASA's ANOPP-Research (Aircraft NOise Prediction Program) tool [82] to predict noise for each component and finally build a noise emission estimation for the aircraft.…”

Noise of Future Aircraft Propulsion: Sources and Design Considerations

“…Furthermore, for nonaxisymmetric flows, the first and second BPF are overtoping by far the third tone. Clark et al (2018) work was on NASA's BLI D8 doublebubble concept . Two phenomena are studied, the ingestion of turbulence and the nonuniform flow intake.…”

“…Two phenomena are studied, the ingestion of turbulence and the nonuniform flow intake. Turbulence ingestion, according to Clark et al (2018), can produce tonal components caused by blade passage through turbulence. At the same time, random fluctuations caused by turbulence generate unsteady loading leading to broadband noise.…”

“…The geometry of the tail must be carefully selected to improve shielding and reduce scattering. That is because engine bellow tale can increase scattering towards the ground (Clark et al, 2018). Furthermore, when positioned at the back, it should be avoided to have tail support geometry in front of the inlet of BLI engines, since it produces unsteady loading due to non axisymmetric flow (Petrosino et al, 2021) .…”

Fan Noise Boundary-Layer Ingestion Installation Effects for NOVA Aircraft Configuration

“…They found that the dominant mechanism for changes in far-field rotor shock noise due to the boundary layer ingestion at low free-stream Mach numbers is the ingestion of stream-wise vorticity. A noise assessment at aircraft-level for the NASA D8 concept has been carried out by Clark et al 19 by using the Aircraft NOise Prediction Program (ANOPP) comprehensive tool to predict the noise generated by each source component, with the BLI influence on fan noise empirically modeled with experimental data. In that study, boundary layer ingestion was predicted to have a detrimental impact on effective perceived noise levels in the order of 15 dB.…”