Drone delivery continues to advance in terms of technology and with the take-up by different companies. One of the downsides of the future expansion of drones will be the noise, with the hum generated by rotors filling the sky.
To seek quitter drones, NASA has awarded $5.7 million to a multi-university partnership. Leading the discovery of quieter vertical lift air vehicles is Boston University, together with Virginia Tech, Embry-Riddle University, Tuskegee University, and the company Joby Aviation.
Electric vertical take-off and landing (eVTOL) vehicles typically have four or more rotors and increased traffic, and industrial activity will make cities louder and louder, adding to the already existing noise pollution.
The research will develop methods to better predict low noise operations of such vehicles within the urban canyon. The research team will also explore how much the ingestion of large-scale disturbances during flight, such as gusts of winds, also affect rotor noise.
The use of multiple rotors is necessary for achieving additional degrees of freedom. However, this makes noise reduction more complex.
The researchers will be seeking to determine the optimal configuration for safe operations in unsteady environments that also produce low noise. The investigations will include both computational and experimental methods.
Much of the practical work will take place at Virginia Tech, including testing prototypes in a specially designed space called the Stability Wind Tunnel. This space is equipped for aerodynamic and aeroacoustic testing. This is a branch of acoustics that studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces.
The Stability Wind Tunnel can assess low background noise and measure other performance factors like aeroacoustic flow. To assess noise, the tunnel has a 251-channel microphone array and stereoscopic particle image velocimetry systems.
The researchers will be mainly focusing on the rotors, considering revolutions per minute, thrust, torque, and noise from a variety of angles, as well as the flow field in and around those rotors. Computerised systems will help to assess real flow and noise data acquisition and processing.
The methods and data derived from this study will be open-sourced and therefore the data will also aid the drone manufacturing industry to advance vertical lift air vehicles.
The research will also provide graduate and undergraduate students hands-on research experience related to the urban air mobility industry, thereby pushing the science and technology of drones further as the quest for quieter flying machines takes place.