Studies on the acoustic far-field distance of urban air mobility aircraft
Open Access
- Author:
- Hur, Keon Wong
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- January 25, 2023
- Committee Members:
- Amy Pritchett, Program Head/Chair
Kenneth Steven Brentner, Thesis Advisor/Co-Advisor
Eric Greenwood, Committee Member
James George Coder, Committee Member - Keywords:
- Multirotor
UAM
sUAS
eVTOL
Aeroacoustic
Far-field
OpenVSP
VSP2WOPWOP
CHARM
PSU-WOPWOP
Noise prediction - Abstract:
- The noise generation of multirotor aircraft, including urban air mobility (UAM) aircraft, must be understood to integrate these aircraft into the transportation infrastructure. In general, a far-field characterization of aircraft noise is desirable, because the measured or predicted noise can be readily generalized from one far-field distance to any other, whereas in the near field, this generalization is not applicable. Therefore, the purpose of this thesis is to provide guidance on determining the far-field distance for multirotor aircraft so that measurements are made in a far field, where acoustic pressure waves dominate the signal. The coupled system of OpenVSP (generating the computational geometry of aircraft components), VSP2WOPWOP or CHARM (both used for computing the air loads) and PSU-WOPWOP (Ffowcs Williams-Hawkings equation for the tonal noise and Brooks, Pope, and Marcolini model for the broadband noise predictions) is used for the research. The far-field distance for an approximate S-76 model, small uncrewed aircraft systems (sUAS), and a generic electric vertical take-off and landing (eVTOL) were examined. Regarding the sUAS far field studies, the number of rotors was varied (from 1 to 4, 6, and 8: i.e., a single rotor, quadcopter, hexacopter, and octocopter) to examine its effect on the far-field distance. Proportionality between the number of rotors and far-field distance was found when the distance was normalized by the rotor diameter. In addition, the effect of vehicle size on the far-field distance was inspected to see whether changing the size of the vehicle would affect the result. To consider vehicle size, the arm lengths of the quadcopter were varied to be 0.7, 2.1, and 3.5 rotor diameters. As in the case where the number of rotors was varied, proportionality between the vehicle size and far-field distance was found when the distance was normalized by the rotor diameter. When the distance was normalized by the vehicle diameter, it was found that far-field distance ranged from 1.5 to 2.0 vehicle diameters for all the cases in the numbers of rotors and vehicle size studies. This suggests the possibility of setting up a general rule for the far-field distance based on sUAS vehicle size. For the generic eVTOL studies, both hover and forward flight were examined. Compared to the sUAS case, the result showed a larger value of far-field distance, 5.4 vehicle diameters, for both cases of hover and forward flight, assuming the noise source is the full vehicle. This difference is likely from multiple reasons including: different operating conditions, higher fidelity aerodynamic models, and computational procedures. This result implies that there may be additional parameters needed for a consistent rule to estimate far- field distance among different configurations of larger multicopters.