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

Abstract

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

Numerical Investigation of a Shielded Chevron Nozzle

“…However, at high frequencies CFD underpredicts noise for the baseline nozzle by nearly 6 dB. AAPL tests indicated an increase in low-frequency noise at upstream and broadside angles 14 to the jet axis, corresponding with a trailing edge dipole caused by the turbulent jet interacting with the trailing edge of the test planform. As mSrc is only intended to predict jet noise and has no functionality for trailing edge noise, the noise predictions from CFD will not include the trailing edge dipole.…”

“…AAPL uses the Nozzle Acoustic Test Rig (NATR) 13 to simulate flight conditions with a 53 inch diameter free jet which exits a few feet upstream of the nozzle. Further description of the AAPL facility and discussions of test results including far-field noise 14 , PIV data 15 , and phased array measurements 16 can be found in companion papers. Previous simulations have shown a negligible difference in results between modeling the Mach 0.3 free jet with a surrounding quiescent flow; or ignoring the cylindrical NATR free jet and setting a uniform freestream Mach number of 0.3 with no surrounding quiescent flow.…”

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

“…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.…”

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

“…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.…”