Advancing the next generation of quiet flight
By Russell Powers, Ian Clark and Reda Mankbadi|December 2024
The Aeroacoustics Technical Committee addresses the noise produced by the motion of fluids and bodies in the atmosphere and the responses of humans and structures to this noise.
In February, the Connecticut-based RTX Technology Research Center in collaboration with NASA’s Langley Research Center in Virginia tested an additively manufactured triply periodic minimal surface acoustic liner as part of FAA’s Center of Excellence for Alternative Jet Fuels and Environment Project 79 with Pennsylvania State University. The tests were conducted in the Grazing Flow Impedance Tube at NASA Langley in conditions representative of commercial aircraft engines, raising the prospects of incorporating these geometrically complex structures into the next generation of turbofan engines.
In April, OptiNav Inc. of Washington measured the noise produced by the leading edge of a rotor blade in ambient turbulence via a digital microphone array and functional beamforming. Researchers presented the results to the NASA Urban Air Mobility Noise Working Group to support the development of outdoor research measurement protocols and guidelines, particularly for understanding UAM vertiport noise.
Also in April, researchers at the University of California, Irvine conducted initial tests on a new technique for noise reduction from high-speed jets that relies on localized, parallel injection of secondary air. The intent is suppression of noise relevant to carrier deck crew by reducing the efficiency by which turbulent eddies generate noise. Out of nine tested configurations, the best configuration achieved a reduction of 3.4 A-weight decibels. The experiments are to continue with near-field noise measurements, including reflections from simulated surfaces of the carrier deck.
The 30th AIAA/CEAS Aeroacoustics Conference was held at the beginning of June in Rome and featured the most total presented papers ever at an AIAA/CEAS aeroacoustics event. During the conference, the 2024 Aeroacoustics Award was presented to Krishnamurthy Viswanathan for his experiments on aircraft engine noise and his development of noise reduction concepts for turbofans.
In June, researchers at NASA Langley and NASA’s Ames Research Center in California completed a four-year technical challenge on assessment of UAM operational fleet noise. This challenge was under the NASA Revolutionary Vertical Lift Technology project and supports the NASA Aeronautics Research Mission Directorate vision for “safe, quiet, and affordable vertical lift vehicles.” Key accomplishments include the development of community noise modeling methods with FAA’s Aviation Environmental Design Tool and psychoacoustic annoyance models that account for vehicle sound quality and ambient environmental noise.
In July, researchers from the U.S. Army and NASA’s Revolutionary Vertical Lift Technology project completed a comprehensive acoustic flight test campaign at Sierra Army Depot in California. Ground-based microphone arrays recorded noise from an instrumented MD-530 helicopter to guide future UAM flight test techniques and characterize the noise generated by a novel main rotor blade set. The test vehicle flew 11 sorties to meet all test objectives, which included investigating a new snapshot array design, increasing flight test efficiency, making phased array measurements for rotating source separation and localization, ground board sizing studies, and increasing the overall experience of the flight test team.
In April, some 60 high school students from Ohio visited NASA’s Glenn Research Center as part of the culminating event of the Acoustic Damping Capstone Project. Thousands of middle school and high school students nationwide discovered NASA’s aviation noise reduction research via the project, which education program specialists and researchers at NASA Glenn created in 2016. Four of the eight universities in NASA’s Minority University Research and Education Project’s Aerospace Academy also participated. The University of Texas at El Paso constructed 75 simplified normal incidence impedance tubes, reaching 1,200 students.
Contributors: Robert Dougherty, L. Danielle Koch, Jeffrey
Mendoza, Dimitri Papamoschou, Kyle Pascioni, Stephen Rizzi and James Stephenson