Numerical Investigation of a Shielded Chevron Nozzle

2019

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

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2019

“…Significant findings of this effort are presented in this paper. Measurements of the far-field sound 6 and of noise source distributions 7 and predictions of the flow and noise of these configurations from Reynolds-Averaged Navier-Stokes simulations 8 are also reported in this conference.…”

Section: Introductionmentioning

confidence: 91%

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

Wernet

2019

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 •

“…Noise source distributions measured with a phased array are presented in this paper. Companion papers are also being presented at this conferenced including: measurements of the far field sound 3 , particle image velocimetry of the jet plume 4 , and computational work using Reynolds-Averaged Navier-Stokes 5 . Collectively this work describes the jet plume, noise sources, and radiated sound that can be expected from this configuration.…”

Section: Introductionmentioning

confidence: 99%

Translating Phased Array Measurements of a low-noise top-mounted propulsion installation for a supersonic airliner

Cluts

Podboy

2019

A novel translating-phased-array technique was applied during a model-scale validation test of low-noise propulsion concepts for supersonic transport aircraft. Data were acquired for a series of nozzles with different chevron designs, both uninstalled and installed on a representative aircraft planform. The far field data confirmed the noise reduction potential of top-mounted installation, while the phased array results gave insights into how the reduction occurred and highlighted areas for improvement. This was the inaugural test for the new translating phased array, which measures source maps as seen by observers at different polar angles. Propagation effects through the free jet were documented for the different viewing angles. The source maps obtained were used to understand important aspects of the far field noise measurements.