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Anti-Phase Rotor Noise Suppression Technology Experimentally Confirmed
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Anti-Phase Rotor Noise Suppression Technology Experimentally Confirmed

A series of acoustic tests have been conducted in an anechoic chamber at Pennsylvania State University (PSU) during the week of July 26, 2019, to validate a novel anti-phase rotor-noise suppression technology developed by NASA Ames under the Center Innovation Funds program. Unlike conventional rotors, the anti-phase rotor technology employs a waveform pattern on the rotor blade trailing edge with a 180-degree phase shift from one blade to another blade in a typical two-bladed rotor. Computational Fluid Dynamics (CFD) confirms the effectiveness of this technology and identifies a four-period waveform-trailing anti-rotor design as the most optimal. This is also confirmed independently in analysis provided by Continuum Dynamics, Inc. (CDI), who provided technical consulting at no cost to NASA. Acoustic experimental results have confirmed the noise suppression capability of the anti-phase rotor. The novel design produces lower noise than the conventional rotor at all low frequencies, especially at odd integers of the rotor frequency where most of the noise peaks are sharply reduced or essentially eliminated. Up to 4 dB noise reduction in the broadband frequency is observed with the anti-phase rotor. The experimental results provide direct evidence of the potential noise suppression of the proposed technology, which could contribute to future noise-reduction designs for multi-rotor Unmanned Aircraft Systems (UAS) and Urban Air Mobility (UAM) vehicles.

BACKGROUND: UAS and UAM vehicles typically employ a multi-rotor design for Vertical Take-Off and Landing (VTOL). Noise annoyance is one of the greatest barriers to public acceptance of UAS and UAM operations in the National Airspace System (NAS). Rotor noise sources come from rotor blade interactions as they fly into their own vortices, and from the vortices generated by other blades. This in turn creates a harmonic reinforcement of the vortex structure as the blades go around that results in a significant noise intensity affecting community noise. The anti-phase design introduces mechanisms that breakup the vortex harmonic reinforcement by employing a phase-shift and trailing-edge waveform pattern on the rotor blade design. This design causes the wake shed of the preceding blade to ‘miss hitting’ the following blade, thus resulting in a weaker vortex structure that leads to a noise reduction. Active control designs of the anti-phase rotor technology can also be employed to provide the ability to customize the noise reduction depending on the operating conditions of rotorcraft vehicles.

NASA PROGRAM FUNDING: Center Innovation Funds (CIF) project, NASA Ames Center Chief Technologist (CCT)

CIF TEAM: Nick Cramer, David Kinney (AA), Nhan Nguyen, Jose Palacios (PSU), Daniel Wachspress (CDI), Juntao Xiong, Sihong Yan (PSU), and Raja Zahirudin (PSU)

POINT OF CONTACT: Nhan Nguyen, nhan.t.nguyen@nasa.gov

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