Design of Efficient Propellers Using Variable-Fidelity Aerodynamic Analysis and Multilevel Optimization

Abstract

A multilevel design optimization framework was developed for the aerodynamic design of an electric aerial vehicle propeller in cruise conditions. The objective was to determine the optimum propeller shape to minimize torque at a given required thrust level and thus maximize overall propeller efficiency. A key concept of the design is the sequential application of a three-dimensional planform and two-dimensional section designs iteratively to make the best use of the complementary characteristics of gradient-free and gradient-based optimization strategies and the corresponding parameterization of the design space. Variable-fidelity aerodynamic analyses of blade element momentum theory and Navier-Stokes solutions were used to achieve computational efficiency and high accuracy. First, the optimal planform shape was determined by adjusting radius, twist angle, and chord lengths of the blade. Subsequently, the sectional airfoil design was performed at several spanwise locations. Given the new airfoil sections, the planform was redesigned to consider three-dimensional flow effects. The final optimized propeller design was validated using three-dimensional Navier-Stokes flow solvers and was tested in a wind-tunnel facility. Propeller efficiency was found to be improved by 5.7%. Finally, the fluid-structure interaction was analyzed to confirm that a required safety factor was ensured.