Time-Varying Rotor Noise Computations and Analysis of Electric Vertical Take-Off and Landing Aircraft
Open Access
Author:
Gan, Ze Feng
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 24, 2021
Committee Members:
Amy Pritchett, Program Head/Chair Kenneth Steven Brentner, Thesis Advisor/Co-Advisor Eric Greenwood, Committee Member
Keywords:
aeroacoustics rotorcraft simulation broadband noise prediction urban air mobility UAM electric VTOL aircraft variable RPM PSU-WOPWOP
Abstract:
This thesis makes contributions to two important aspects of computing the time-varying rotor noise of electrical vertical take-off and landing (eVTOL) aircraft for urban air mobility (UAM) applications: the time variation of rotor broadband noise, and noise due continuously-varying rotor angular speed.
The noise prediction software PSU-WOPWOP was updated to compute the broadband noise spectrum as a function of observer time within a rotor period. Time-varying broadband noise spectra and directivity computations for helicopter main rotors in forward flight show significant modulation with the blade passage frequency, due to convective amplification and retarded-time effects. Qualitative agreement between noise predictions and flight test data was obtained.
The noise prediction software PSU-WOPWOP was also updated to compute the discrete frequency noise of rotors with continuously-varying rotational speed, which may require accepting input kinematics and aerodynamic loading data at unevenly-spaced source time intervals. Order of magnitude analysis and numerical simulations demonstrated that thickness noise modulations caused by variable rotor speed are primarily due to the time variation of instantaneous rotor speed, rather than angular acceleration, for typical rotor speed variations expected for manned eVTOL aircraft.
