Anti-Phase Vortex Reduction Control for Rotor Noise Suppression

The approach is to develop two rotor noise suppression concepts. One is an alternating trailing edge feature along the blade span in an anti-phase fashion such that the alternating feature is 180o out of phase from blade to blade. This design can disrupt blade vortex interaction, thereby reducing acoustic and vibration signatures. The alternating pattern can have regular or irregular varying spacing from blade to blade to prevent harmonic vortex reinforcement in the blade spanwise direction. The antiphase trailing edge creates a non-planar wake, thus reducing the vortex impingement on the following blade, as confirmed by CFD. The effect is equivalent to a stacked rotor design. The alternating trailing edge can also produce more thrust at the same rotor RPM which has been confirmed experimentally. The anti-phase concept can also be an active control design with the anti-phase trailing edge prescribed by a series of actuated flaps connected by flexible materials.

Rotor noise is one of the biggest issue for civilian and military rotorcraft, multi-rotor UAS and emerging UAM (Urban Air Mobility) aircraft employing rotors for VTOL. Rotorcraft operation during night-time is sharply curtailed due to noise issues. Military applications of rotorcraft require low acoustic signatures to avoid detection. Operating scenarios are forecast to have from hundreds to thousands of UAS and to lesser extent UAM aircraft operating in the crowded urban airspace, the noise pollution is projected to be a huge health and environmental issue. The objective of this proposal is to develop an anti-phase rotor noise suppression technology and to conduct acoustic CFD simulations and experimental validation in an anechoic chamber for a target noise reduction of at least 30% in dBA from a conventional rotor design.

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