Active Noise Control of Multirotor Advanced Air Mobility Vehicles

An active noise control technology is developed here to reduce the in-plane thickness noise associated with multirotor advanced air mobility Vehicles. The basic concept is that few actuators (e.g., microspeakers) are embedded into the blade surfaces. They emit a loading signal to cancel the thickness noise. This actuation signal is determined via the FfowcsWilliams-Hawking (FWH) formula. We considered here two inline rotors, and we showed that the FWH-determined actuation signal can produce perfect cancellation at a point target. However, the practical need is to achieve noise reduction over an azimuthal zone, not just a single point. To achieve this zonal noise reduction, an optimization technique is developed to determine the required actuation signal produced by the on-blade distribution of embedded actuators on the two rotors. For the specific geometry considered here, this produced about 9 dB reduction in the in-plane thickness noise during forward flight of the two rotors. We further developed a technology that replaces using a point actuator on each blade by distributed microactuator system to achieve the same noise reduction goal with significantly reduced loading amplitudes per actuator.