Ruthvik Chandrasekaran
(Advisor: Prof. Dewey H Hodges)

will propose a doctoral thesis entitled,

Performance Advantages and Resonance Analysis

of a

Variable Speed Rotor Using Geometrically Exact Beam Formulations

On

 Monday, October 26 at 10:00 a.m. (Eastern)
BlueJeans Link:  https://bluejeans.com/7576730461/

Abstract

The efficiency and operating envelope of a rotorcraft is constrained by the speed of the rotor. Most of the helicopters operate with a constant rotor speed. Varying the speed of the rotor based on the operating condition could significantly improve the rotor performance. In this study, a hingeless rotor model with elastic blades is built in DYMORE to study various aspects of Variable Speed Rotor (VSR) technology. The rotor blades are modeled as one-dimensional beams using state of the art beam theory known as geometrically exact beam theory. A comprehensive unsteady aerodynamics model with dynamic stall and finite-state dynamic inflow is used to obtain the aerodynamic loads acting on the rotor. A wind tunnel trim procedure is adopted to trim the rotor for a given thrust, roll and pitch moment. An auto-pilot controller is used to trim the rotor during time marching based on the wind tunnel trim values. The rotor model and trim procedure is validated using results from literature. The power savings that can be achieved at various advance ratios by varying the speed of the rotor is evaluated. However, varying the rotor speed leads to vibration issues as the rotor passes through the resonance regions. In this region, the rotor blade's natural frequency coincides with the multiple of rotor's operating frequency. This leads to an increase in vibratory loads. All the resonance points are identified from the fan plot of the rotor blade. It is observed that the lead-lag moment at the blade root increases significantly compared to the nominal value during lag resonance. It is also observed that the flap and torsional moments increase during lag resonance.

Hence, a comprehensive rotor model incorporating geometrically exact beam theory is built in the present work to analyze hingeless variable speed rotors. Transition dynamics of the rotor blade for different operating conditions will be analyzed further. Methods of vibration reduction during resonance will also be studied during the rest of our analysis.

Committee

• Prof. Dewey H Hodges, School of Aerospace Engineering, Georgia Institute of Technology
• Assoc. Prof. Graeme J Kennedy, School of Aerospace Engineering, Georgia Institute of Technology
• Prof. David A Peters, McKelvey School of Engineering, Washington University in St. Louis