Helicopter Rotor Morphing for Performance Improvement in Reverse Flow Conditions

The present study focuses on morphing of the inboard section of a helicopter rotor blade to improve aerodynamic performance in high-speed flight with significant reverse flow. Starting with the SC325218 airfoil, CFD simulations show that morphing only its lower surface, aft of the spar, to a modified ellipse geometry results in a significant reduction of reverse flow drag on the retreating side while limiting aerodynamic penalties in normal flow conditions on the advancing side. The study develops a morphing structure concept that transitions between the SC325218 airfoil and the derivative geometry while being able to carry aerodynamic loads. Key to this concept is the design of a morphing cellular lattice in the mid-chord region (25-65% chord), operating in collaboration with a specialized two-segment lower surface skin, and actuation ribs connected by spanwise stringers which also support aerodynamic loads in the aft-chord section. The cellular lattice’s geometry is determined through optimization and the lattice is successful in morphing to the target geometry for high-speed operation. Parametric variations in lattice modulus, lower surface compliant skin modulus, and actuation strain are conducted toward minimizing actuation load and peak lattice strains, and key insight into the operational aspects of this morphing system are developed.