Addressing noise challenges in the mobility market

By JULIAN WINKLER, VLADIMIR GOLUBEV AND REDA MANKBADI|December 2020

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.

The development of urban air mobility concepts has led to increased research in the aeroacoustics community to address the noise challenges in this emerging market. In October, the NASA and FAA-led Urban Air Mobility Noise Working Group published a white paper, “Urban Air Mobility Noise: Current Practice, Gaps, and Recommendations,” as a NASA Technical Publication. The paper provides noise guidance to mobility stakeholders in the areas of predictive tools and technologies, ground and flight testing, human response and metrics, and regulation and policy.

Examples of UAM-focused acoustic analysis technologies include UCD-QuietFly, a new broadband noise prediction tool for UAM aircraft developed using a state-of-the-art empirical wall pressure spectrum model by University of California, Davis, in partnership with Hyundai Motor Co. and distributed to several universities and companies developing electric vertical takeoff and landing, or eVTOL, vehicles. UCD-QuietFly is designed to accurately and efficiently predict multirotor trailing-edge noise, which is dominant at high frequencies.

Separately, a team of researchers at Embry-Riddle Aeronautical University in Florida in January performed hybrid high-fidelity simulations of the flow and acoustic field around a propeller like those on consumer drones and quadcopters. This simulation approach provides a framework for studying multirotor interactions with the capability to accurately predict both tonal and broadband noise components.

New York-based Moog Inc. and NASA’s Glenn Research Center in Ohio conducted field testing of UAM noise for the SureFly eVTOL at the Lunken Municipal Airport in Cincinnati. Researchers completed data analysis from these acoustic tests in February. The results will help to characterize sound sources from advanced air mobility vehicles, NASA’s term for the new class of electric vehicles that would introduce regular aviation services to regions with few if any such services. The class includes cargo and UAM designs as well as their precursors. Tests are planned for hover and flyover acoustic measurements.

Developments in experimental capabilities to characterize and identify noise sources during flight and in rig tests have led to more sophisticated approaches. ATA Engineering Inc., headquartered in San Diego, and the University of California, Irvine, have extended the continuous-scan acoustic measurement paradigm to problems involving propulsion airframe aeroacoustics for rig testing. Linearly traversing microphone array measurements conducted in January at UCI on a small-scale ducted fan were used for source characterization and prediction of complex interference patterns generated from scattering past a rigid plate, using the boundary element method.

In August, a collaboration between researchers at NASA’s Langley Research Center in Virginia and Boeing culminated in an innovative acoustic flight test conducted in Montana using an Etihad Airways Boeing 787-10 aircraft as part of the Boeing ecoDemonstrator program. The test collected data from approximately 1,200 microphones on the ground and on the aircraft for special flight conditions and maneuvers, and the data will advance noise design tools, propulsion airframe aeroacoustic technologies for future low-noise aircraft and novel methods for low-noise operations.

In April, under congressional direction, FAA posted a Notice of Proposed Rulemaking regarding landing and takeoff noise standards for new supersonic airplanes. A new noise standard is needed to provide regulatory certainty for manufacturers of new supersonic airplanes under development. NASA assisted FAA in developing the standards by providing performance and noise predictions of notional supersonic aircraft.

In June, researchers at Embry-Riddle simulated rocket launch supersonic noise reduction via water injection from the launch pad by extending large-eddy simulations to multiphase flows. They identified two important mechanisms for noise suppression: increased turbulent mixing imposed by high-density water and momentum transfer between the wall boundary layer and the water injection flow.

Contributors: Samuel Afari, Jeffrey Berton, Ian Clark, Dennis Huff, Seongkyu Lee, Stephen Rizzi, Sam Salehian and Parthiv Shah