Noise Scaling and Community Noise Metrics for the Hybrid Wing Body Aircraft

Abstract

An aircraft system noise assessment was performed for the hybrid wing body aircraft concept, known as the N2A-EXTE. This assessment is a result of an effort by NASA to explore a realistic HWB design that has the potential to substantially reduce noise and fuel burn. Under contract to NASA, Boeing designed the aircraft using practical aircraft design principles with incorporation of noise technologies projected to be available in the 2020 timeframe. NASA tested a 5.8% scale-model of the design in the NASA Langley 14-by 22-Foot Subsonic Tunnel to provide source noise directivity and installation effects for aircraft engine and airframe configurations. Analysis permitted direct scaling of the model-scale jet, airframe, and engine shielding effect measurements to full-scale. Use of these in combination with ANOPP predictions enabled computations of the cumulative (CUM) noise margins relative to FAA Stage 4 limits. The CUM margins were computed for a baseline N2A-EXTE configuration and for configurations with added noise reduction strategies. The strategies include reduced approach speed, over-the-rotor liner and soft-vane fan technologies, vertical tail placement and orientation, and modified landing gear designs with fairings. Combining the inherent HWB engine shielding by the airframe with added noise technologies, the cumulative noise was assessed at 38.7 dB below FAA Stage 4 certification level, just 3.3 dB short of the NASA N+2 goal of 42 dB. This new result shows that the NASA N+2 goal is approachable and that significant reduction in overall aircraft noise is possible through configurations with noise reduction technologies and operational changes. Nomenclature ANOPP = NASA's aircraft noise prediction program 1 ANOPP2 = NASA's aircraft noise prediction program2, a multi-fidelity framework AOA = angle of attack, degrees AP = approach flight condition BENS = broadband engine noise simulators BPR = engine bypass ratio CB = cutback flight conditionThis material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AIAA Aviation 2 CJES = compact jet engine simulators CUM = cumulative noise (summation of takeoff, cutback and approach EPNL), EPNdB D = fan nozzle exit diameter, ft. dB = decibel EPNL = effective perceived noise level, dB, also referred to as EPNdB FLOPS = flight optimization system 2 f = frequency HWB = hybrid wing body LE = leading edge L/D = lift/drag M = Mach number PNL = perceived noise level, dB PNLT = tone-corrected perceived noise level, dB R = distance from source to observer SF = model-scale/full-scale = 0.058 SFC = specific fuel consumption SL = sideline (full-throttle flight condition) certification point SPL = sound pressure level X = axial coordinate, ft. Greek φ = azimuthal directivity angle, degrees θ = polar directivity angle, degrees Subscript fs = full-scale ms = model-scale nb = narrowband

Shielding of Turbomachinery Broadband Noise from a Hybrid wing Body Aircraft Configuration

“…The effects of engine placement and verticals configuration on the shielding of the BENS exhaust noise radiation are examined in this section. A particular focus is on the 31.5 kHz model scale one-third octave band frequency as it corresponds to the peak frequency (about 540 Hz full scale) for turbomachinery noise 8 .…”

“…Multi-positional jet engines and broadband engine noise simulators were also developed by NASA for shielding testing. Aspects of the test, reported in this and companion papers [5][6][7][8][9][10][11][12] , are the examination of noise shielding parameters (such as engine location, vertical and nozzle configurations) with regard to noise emission, and the determination of the noise spectra, levels, and directivity of the base vehicle and its components. Finally, the results from this test are used to support the noise assessment 7 of this HWB design and to validate the "low noise" characteristics of this aircraft concept.…”

Jet noise shielding provided by a hybrid wing body aircraft

“…Thus, a factor of 4.55 dB has been added to the data shown in Figure 9(c) based on the scaling of mixed jet velocity to the eighth power: 80 log 10 (U mix desired /U mix actual ). The contours in Figure 9 undergo additional scaling and extrapolation as detailed in Burley et al 17 to generate the expected jet noise contribution to the HWB community noise assessment.…”

“…While the current manuscript describes the jet noise investigations, colleagues involved in other aspects of the test have provided companion papers describing the microphone phased array development, 11 acoustic calibration procedures, 12 acoustic data processing, 13 shielding characteristics of a mode-generating source, 14 shielding of broadband turbomachinery noise, 15 airframe noise, 16 and community noise metrics. 17 The current study provides an overview of the jet noise portion of the HWB acoustic test and focuses on the shielding benefits observed in conjunction with both the baseline axisymmetric nozzle system and the low noise nozzle system as the engines are translated relative to the fuselage trailing edge. Acoustic results from both the tower/truss arrangement and the overhead phased array are presented in this work.…”

Low-speed Aerodynamic Investigations of a Hybrid Wing Body Configuration

“…The first test focused on measuring the basic low-speed aerodynamics 9 while the second was an acoustics test. [10][11][12] The third test focused on characterizing the nacelle inlet flow conditions through particle image velocimetry (PIV) measurements. The acoustic test results will not be covered in this paper, only the low-speed aerodynamic tests.…”