Computational Modeling of Variable-Droop Leading Edge in Forward Flight

In recent years, there has been significant interest in on-blade concepts that expand the operating envelope of helicopters without compromising the performance characteristics of the baseline rotor. The variable-droop leading-edge concept is explored in a modified version of the Navier-Stokes solver OVERFLOW. Modifications were made to the solver to allow deforming-grid capability. This concept was explored in dynamic stall tests of the VR-12 and SC1095 helicopter airfoils. The variable-droop leading-edge airfoils have dramatically reduced drag and moment rises associated with dynamic stall. Using the results of these tests, a modified UH-60A rotor incorporating variable-droop leading-edge airfoils was analyzed using loosely coupled computational fluid dynamics and comprehensive structural dynamics with OVERFLOW and DYMORE and compared with the standard UH-60A rotor for high-thrust-case flight 9017. Results show a reduction in the peak negative pitching moment. The rotor efficiency was shown to improve by 2.9% and the 4/rev component of vertical force reduced by 8%. These performance improvements can be improved with an improved droop schedule and by incorporating improved transonic airfoils.