Aeroacoustic Validation of Installed Low Noise Propulsion for NASA’s N+2 Supersonic Airliner

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A model-scale exhaust system was tested to validate low-noise concepts and noise prediction methods. The tests acquired far-field acoustics, acoustic source distributions, and turbulent velocity statistics; this report covers the far-field acoustic measurements. Data were acquired for a series of nozzles with different chevron designs, both uninstalled and installed on a representative aircraft planform. The impact of the various chevron treatments on the far-field noise was documented, along with the impact of the pylon and planform. For the baseline nozzle, installation produced a 2EPNdB reduction, as was assumed in system studies. Chevrons were used to shift noise sources upstream to maximize the installation benefits and to reduce unshielded sources downstream. These resulted in reductions of 4-5EPNdB relative to the uninstalled baseline nozzle. Detailed analysis of spectral directivities behind the integrated EPNL metric gave insight into how well these concepts actually work. When correlated with particle image velocimetry measurements and phased array measurements, reported in companion papers, the explanation of acoustic benefits from top-mounted propulsion is clear, as is the path toward optimization of the concept. NomenclatureEPNL Effective Perceived Noise Level IVP Inverted Velocity Profile M∞ flight Mach number NPRp nozzle pressure ratio of primary stream NPRf nozzle pressure ratio of fan streams PSD power spectral density of sound pressure

“…The flight stream was M∞= 0.3 for all test points. The data were transformed to M∞= 0.38 using procedures documented in previous tests 3 for EPNL analysis.…”

Section: Flow Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Noise measurements of a low-noise top-mounted propulsion installation for a supersonic airliner

Bridges

2019

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“…In previous testing 1 , greater acoustic benefit was found from installation than any other technology for a given engine. A propulsion system mounted on the top of the aircraft had substantial (2-3EPNdB) shielding of jet mixing noise in the frequency range of peak human annoyance.…”

Section: Introductionmentioning

confidence: 96%

PIV measurements of a low-noise top-mounted propulsion installation for a supersonic airliner

Bridges

Wernet

2019

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A model-scale exhaust system was tested to validate low-noise propulsion concepts and noise prediction methods. The tests, referred to as the Top-Mounted Propulsion 2017 (TMP17) tests, involved far-field acoustics, phased array, and particle image velocimetry (PIV). This paper covers the particle image velocimetry portion. Data were acquired at NASA Glenn's Aero-Acoustic Propulsion Lab for a series of nozzles with different chevron designs, both uninstalled and installed on a representative aircraft planform. The impact of the various chevron treatments on the turbulent velocity field was documented, along with the impact of the pylon and planform. When correlated with far-field acoustic measurements and phased array measurements, reported in companion papers, the explanation of acoustic benefits from top-mounted propulsion is clear, as is the path toward optimization of the concept. Nomenclature c speed of sound IVP Inverted Velocity Profile M Mach number NPR nozzle total pressure ratio NTR nozzle total temperature ratio T temperature TKE turbulent kinetic energy TMP17 Top-Mounted Propulsion test 2017 u, v, w jet velocity components U = ⟨u⟩ x axial coordinate Subscripts p, f primary, fan streams j jet exit mix fully mixed ∞ ambient Other ⟨•⟩ average of •

“…This has been shown to offer significant noise reduction from both the fan and the exhaust system 4 . Recent tests at NASA Glenn Research Center have indicated a 3-4 EPNdB benefit from top-mounted engine installation relative to an underwing configuration 5 . Combined with chevrons, top-mounted propulsion can shield the high-frequency sources close to the nozzle exit and lessen the penalty associated with enhanced mixing.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of a Shielded Chevron Nozzle

Heberling¹

2019

Reynolds-Averaged Navier-Stokes simulations have been performed on a three-stream inverted velocity profile nozzle with and without various configurations of chevrons attached. The nozzle was mounted on a planform to imitate an engine mounted above a wing, shielding ground observers from engine noise. Several chevron designs intended to aggressively mix the jet and move noise sources upstream for shielding were examined to investigate their effects on noise and thrust. Numerical results for the baseline nozzle and one chevron configuration were compared with far-field noise and particle image velocimetry data obtained in NASA Glenn Research Center's Aero-Acoustic Propulsion Laboratory. A configuration in which chevrons alternate penetration into the primary stream and tertiary fan stream was explored using the Modern Design of Experiments approach. Short, high-penetration chevrons demonstrated a significant noise reduction for a relatively small thrust penalty.