Optimal Active Twist Deployment Schedule of a Rotor for Performance Improvement and Vibration Reduction

In this paper, the best actuation schedules exploiting various waveform types are sought taking advantage of the global search algorithm for the reduction of the power required and/or hub vibration of a rotor in high speed forward flight. The active twist schedules include two non-harmonic inputs formed based on segmented step functions along with the simple harmonic waveform input. An advanced particle swarm assisted genetic algorithm (PSGA) is employed for the optimizer. A rotorcraft computational structural dynamics (CSD) code CAMRAD II is used to perform the rotor aeromechanics analysis. A CFD/CSD coupling is introduced to assist the observations made using the CSD analysis. The PSGA optimization results are verified against the parameter sweep study performed by the harmonic actuation. The best optimum twist schedules according to the performance or vibration reduction strategy are identified and their optimization gains are compared between the actuation cases. A two-phase non-harmonic actuation schedule demonstrates the best outcome in decreasing the rotor power required while a four-phase non-harmonic schedule leads to the best vibration reduction. The mechanism of reduction gains is identified illustrating the section airloads, angle-of-attack distribution, and net elastic twist deformation predicted using CSD and CFD/CSD approaches.