Hybrid Aerodynamic Optimization of a Propeller Based on the Reformulated Blade Element Momentum Theory

A propeller blade has a significant effect on the performance of a propulsion system. It is of great significance to develop an efficient and accurate optimization strategy for propeller design in the preliminary stage. A key concept of the design is to establish a fast hybrid aerodynamic optimization framework employing the reformulated Blade Element Momentum (rBEM) model to optimize the propeller blade shape under cruising conditions. First, the rBEM numerical model is established and validated with the experimental data in both hover and forward-flight cases. Second, a fast hybrid design optimization strategy based on the rBEM model is developed, which divides the propeller design process into gradient-free planform optimization and gradient-based airfoil optimization. The planform and sectional designs are coupled with each other in an iterative manner until convergence criteria is reached. Based on the proposed optimization strategy, the hybrid design process shows gradual convergence. The efficiency of the optimized propeller has been increased by 29.84% when compared with the baseline propeller. The solidity ratio of the optimal propeller is smaller than that of the baseline propeller, which has a smaller chord length distribution, a larger twist angle distribution, and lesser camber and thickness of the cross-sectional airfoil.