Aerodynamic Optimization of Helicopter Rotor Blades using Variable Fidelity Methods

The motivation of this work is to reduce the overall required computational resources of the aerodynamic optimization process of helicopter rotor blades. Therefore an approach already applied to fixed wing aircraft is now ported to the helicopter rotor blade optimization. It is a surrogate based optimization process including variable-fidelity methods. After setting up the framework to accomplish this task, a theoretical and practical investigation of various aerodynamic models ranging from the blade element theory to computational fluid dynamics (CFD) for helicopter rotors is performed. This is done with the 7A model rotor in two flight conditions, namely hover and forward flight.From this examination a potential subset of methods is selected and further analyzed in applied variable-fidelity optimizations. These optimizations are benchmarked with a state of the art single-fidelity process. Potential resource reductions of up to 85 % in computing costs are observed and at the same time unfeasible model combinations are identified. The benefit is demonstrated for two underlying rotor configurations, the 7A model rotor and the reference rotor of the European CleanSky Green Rotorcraft (GRC) research project. While the 7A rotor is parameterized with four design variables, the GRC rotor optimization is performed at a more industrial relevant level with ten design variables and two structural constraints. The final selection of model combinations is the blade element theory enhanced with a prescribed wake model and a multi-bladed chimera setup solving the RANS equations in forward flight, while for hover the solution of the inviscid Euler equations supply the trend for the solution of the RANS equations on a periodic mesh. The employment of the variable-fidelity approach to multi-objective scenarios proves to be highly beneficial and the need to perform multi-objective optimizations for rotor blade design is highlighted. The performed optimizations in this work provide a selection of potential future blade designs