Aerodynamic design of EAV propeller using a multi-level optimization method

Abstract

A multi-level design optimization framework is developed for the aerodynamic design of EAV rotor blades and can be applied to any types of rotor blades during steady-state condition. An objective function is to enhance the aerodynamic performance of rotor blades by reducing the required power to counteract resultant torque and to increase structural safety. The optimization framework applies three-dimensional planform design and two-dimensional sectional design in a sequential and iterative manner. In the first-level planform design, we use a genetic algorithm and flow analysis based on computationally inexpensive blade element momentum theory (BEMT). An optimal planform shape is obtained with the relatively small number of design variables but with large variations. After the initial planform design is conducted, local flow conditions of the blade sections are analyzed using high-fidelity Navier-Stokes CFD flow solvers. Next, the sectional airfoil design is performed at several spanwise locations using a gradient-based optimization algorithm and Navier-Stokes flow analysis. When the optimal airfoil shape is determined throughout the span, the planform is redesigned given the new set of airfoil shapes. Through this iterative design process, not only an optimal flow condition but also an optimal shape of the EAV propeller blade is obtained. The optimized propeller-blade design was tested in a wind tunnel facility at various flow conditions to validate the design results. The efficiency was slightly less than the expected improvement of 9% predicted by our proposed design framework but still sufficiently enhanced the aerodynamic performance of the EAV rotor system.