Helicopter Rotor Shape Optimization for the Improvement of Aeroacoustic Performance in Hover

A helicopter rotor is optimally designed for aeroacoustic performance improvement. As shown in previous reports, the blade shapes can be designed to minimize high-speed impulsive noise but tend to have excessively high tapers and be swept back. Since an overly short chord length around the blade-tip region may cause structural problems and safety issues in autorotation, an autorotation index has been introduced to keep the tip region from having excessive taper ratios. In addition, the changes in thickness and camber of the airfoils can also be taken into account to better represent realistic rotor shapes. Aeroacoustic analysis is performed using Kirchhoff's method coupled with computational fluid dynamics analysis, and the optimization is performed using the kriging-model-based genetic algorithm method. Optimization results are presented that show that the designed blades have improved aerodynamic performance and reduced high-speed impulsive noise characteristics. It is found that a more practical blade shape can be obtained by using airfoil transitions and an autorotation index. The results of the analysis of variance and self-organization map indicate that the taper ratios, the swept back, the tip chord length, the protrusion shape, the camber, and the thickness of the root airfoil are the prominent features affecting the aeroacoustic performance of the rotor.