Performance and Acoustics of Coaxial Counter-Rotating Rotors in Hover and Forward Flight Conditions
Open Access
- Author:
- Mcthane, Eric
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 15, 2023
- Committee Members:
- Eric Greenwood, Thesis Advisor/Co-Advisor
Mark A Miller, Committee Member
Amy Pritchett, Program Head/Chair
Jose Palacios, Committee Member - Keywords:
- Rotor Acoustics
eVTOL
Rotorcraft
Coaxial Rotors
Phase Control
Rotor Performance
Hover
Forward Flight
UAM
Separation Distance
Counter-Rotating - Abstract:
- To understand the aerodynamic performance and acoustics of a coaxial counter-rotating configuration, an experimental study was conducted where the rotor-rotor separation distance was varied in both hover and forward flight conditions. A novel phase control scheme was utilized to maintain a 0◦ blade crossover location for acoustic consistency. As the separation distance is increased from 0.2 rotor radii to 1.1 rotor radii, the higher harmonic tonal noise decreases by around 10 dB. Conversely, the broadband noise increases by around 2 dB with increasing separation distance. The peak frequency of the broadband noise also decreases as separation distance is increased. In hover, the best aerodynamic efficiency was found at a separation distance of 0.4R while the lowest noise was found at 0.65R. As the edgewise flight speed increases from hover to 10 m/s, the total system efficiency decreases on average by 10% . The upper and lower rotor are similarly affected over this speed range. Both higher harmonic tonal noise and broadband noise are also found to increase with increasing flight speed. Increasing the separation distance in edgewise flight speeds at 10 m/s shows an increase on average by around 2% in the overall efficiency of the system. The higher harmonic tonal noise is also seen to decrease by around 6 dB with separation distance. With increasing separation distance, the broadband noise becomes the dominant source of noise in forward flight at 10 m/s. By understanding the acoustic interactions and unsteady loading of coaxial rotors, researchers can devise strategies to maximize efficiency and minimize noise emissions. The physical mechanisms and trends identified in this thesis provide insight to coaxial rotor system designers regarding the key design trades.