Ruthvik Chandrasekaran (Advisor: Prof. Dewey H Hodges)
will defend a doctoral thesis entitled,
Performance Advantages and Resonance Analysis
of a
Variable Speed Rotor Using Geometrically Exact Beam Formulations
On
Tuesday, November 23rd at 2:00 p.m. (Eastern)
Montgomery Knight, Room 317 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. An 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.
Transition dynamics of the rotor blade for different operating conditions were analyzed. Load reduction studies during resonance were carried out by changing the transition times and blade properties. The longer the rotor took to traverse a resonance region, greater were the resonance loads. Increasing the structural damping was a very effective way of mitigating resonance loads. An active system called as the Anti-Resonance System (ARS) was conceptualized and modeled in Dymore. The ARS system was able to effectively remove the resonance loads.
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
 Prof. George Kardomateas, School of Aerospace Engineering, Georgia Institute of Technology
 Assoc. Prof. Julian J. Rimoli, School of Aerospace Engineering, Georgia Institute of Technology