Design and Analysis of Composite Rotor Blades for Active/Passive Vibration Reduction.

Abstract

The problem of vibration has limited the use of helicopters in both civil and military applications. In this research, further analysis has been performed for the various on-blade approaches available for vibration reduction using a unique optimization framework. For passive optimization, an aeroelastic environment with several well-established analysis codes from different sources was developed that can be used to analyze and design composite rotor blades for minimum vibration or maximum performance. This design environment enables conceptual/early preliminary multidisciplinary rotor blade design with realistic structural properties for modern composite rotor blades. For the design of a rotor blade with active twist, a new design strategy was introduced where the amplitude of dynamic twist is maximized. The optimization framework included the aeroelastic design environment described earlier along with surrogate based optimization technique. The surrogate based optimization is performed in combination with Efficient Global Optimization algorithm. Results showed that the amplitude of dynamic twist is a true indicator of control authority of active twist rotor for vibration reduction. Furthermore, the optimization framework was extended to include discrete design variables in the optimization and the solution for mixed-variable design problem was obtained using three different techniques. After modifying the aeroelastic analysis to account for the presence of active flaps, a Mach-scaled composite rotor blade was designed using the same mixed design variable optimization framework to enhance the vibration reduction capabilities of the active flap. In this case also, the amplitude of dynamic twist was used as the objective function and the analysis was carried out at three different spanwise flap locations. This thesis also includes work related to the design and fabrication of a composite rotor blade with dual flaps which can be tested in a Mach-scaled spin test stand. Finally, the use of camber actuation with quadratic and cubic camber deformation shapes for vibration reduction and performance enhancement in dynamic stall region was studied. The aeroelastic analysis was augmented with a modified version of the ONERA dynamic stall model that accounts for morphing airfoil section.