The Effects of Ambient Conditions on Helicopter Harmonic Noise Radiation: Theory and Experiment
Ben Sim, US Army; Eric Greenwood, D. Douglas Boyd, NASA Langley Research Center
May 17, 2016

The Effects of Ambient Conditions on Helicopter Harmonic Noise Radiation: Theory and Experiment
- Presented at Forum 72 - Best Paper for this session
- 18 pages
- SKU # : 72-2016-037 May 2018 Paper of the Month.
- Your Price : $30.00
Join or log in to receive the member price of $15.00!
The Effects of Ambient Conditions on Helicopter Harmonic Noise Radiation: Theory and Experiment
Authors / Details: Ben Sim, US Army; Eric Greenwood and D. Douglas Boyd, NASA Langley Research CenterAbstract
The effects of ambient atmospheric conditions, air temperature and density, on rotor harmonic noise radiation are characterized using theoretical models and experimental measurements of helicopter noise collected at three different test sites at elevations ranging from sea level to 7000 ft above sea level. Significant changes in the thickness, loading, and blade-vortex interaction noise levels and radiation directions are observed across the different test sites for an AS350 helicopter flying at the same indicated airspeed and gross weight. However, the radiated noise is shown to scale with ambient pressure when the flight condition of the helicopter is defined in nondimensional terms. Although the effective tip Mach number is identified as the primary governing parameter for thickness noise, the nondimensional weight coefficient also impacts lower harmonic loading noise levels, which contribute strongly to low frequency harmonic noise radiation both in and out of the plane of the horizon. Strategies for maintaining the same nondimensional rotor operating condition under different ambient conditions are developed using an analytical model of single main rotor helicopter trim and confirmed using a CAMRAD II model of the AS350 helicopter. The ability of the Fundamental Rotorcraft Acoustics Modeling from Experiments (FRAME) technique to generalize noise measurements made under one set of ambient conditions to make accurate noise predictions under other ambient conditions is also validated.
Recently Viewed Items
-
The Effects of Ambient Conditions on Helicopter Harmonic Noise Radiation: Theory and Experiment
- Member Price :
- $15.00
- Your Price :
- $30.00