Design optimization of a controllable camber rotor airfoil

The present study focuses on the design of an actively conformable rotor airfoil. The design consists of several compliant mechanisms of predetermined topology that are placed serially within the airfoil along the chord, aft of the Leading Edge spar, to effectively change the camber. This design requires only a small number of actuators. The study carries out shape optimization of the passive members of the compliant mechanisms along the chord. The designs aim to maximize the vertical airfoil tip deflection under actuation loads, and simultaneously limit the airfoil deflection under aerodynamic loads. This is achieved by two approaches, the first optimizing a single-objective function of actuation tip deflection, and the second optimizing a multi-criteria objective function that contains a ratio of actuation tip deflection and strain energy, representing stiffness under aerodynamic loads. The results of the study indicate that the optimal compliant mechanism shape varies depending on the objective function used as well as other geometric factors. Using the tip deflection objective function the compliant members are relatively uniform in thickness, with flexures developing at the ends of the individual compliant links. Using the multi-criteria objective function the optimized geometry is more complex. The optimal geometry and performance of the compliant mechanism are examined for variations in compliant mechanism unit aspect ratio, maximum allowable passive material, and actuator thickness. The best optimized structures can achieve a trailing edge tip deflection of ±6-8 mm providing an increase in lift of 17-22%.