Higher-Order Free-Wake Method for Helicopter Rotor Aerodynamics

A new higher-order, free-wake method for rotor aerodynamic analysis is presented in this paper. The method uses elements of distributed vorticity to model the lifting surfaces and their wakes. The use of higher-order spanwise elements ensures a higher load resolution compared to traditional filament-based, free-wake methods and does not rely on explicit vortex core modeling that requires user-defined core parameters. Since the present method uses a full-span, singularity-free, relaxed wake, it can resolve the effect of on-blade, partial-span devices. Correlation studies using well-documented experimental data suggest that this free-wake method is capable of accurately predicting the challenging aerodynamics of a helicopter rotor in hover and forward flight. The method provides equal or better level of predictive capability compared to other potential-flow-based methods in its class. Sensitivity studies show that the modeling parameters such as blade panel density and azimuthal time-step size do not have a significant influence on the free-wake solution. Moreover, the method is observed to be numerically well-behaved. The paper concludes with a demonstration of the free-wake method in modeling on-blade, partial-span devices, a capability that will add to the toolset for the design and development of the next generation of rotary-wing aircraft.