# Study of Airfoil Deflections for Unsteady Aerodynamics Optimization in Pitching Airfoils +
###### Abstract  
Camber deflection concepts for a VR-12 rotorcraft airfoil were studied for the optimization of unsteady aerodynamics, including dynamic stall conditions and wing-wing interactions during pitching. The designs are based on deflections of the leading edge and trailing edge sections of the airfoil. The deflection parameters were initially established using Computational Fluid Dynamics (CFD). Results from CFD and Particle Image Velocimetry (PIV) were generated for various leading and trailing edge deflection combinations for comparison of their performances. The conditions of this study are for a Reynolds number of 250,000 and pitching reduced frequency of 0.04, representing a medium regime of rotorcraft operations. Linear tandem tests were performed to simulate unsteady wing-wing interactions. The effects of the deflections are discussed and compared to the baseline. Significant benefits are observed, notably dynamic stall mitigation from the leading edge (LE) deflected wing for certain angles of attack and decrease in the separation regions. Overall, from the numerical simulations and the experimental data fields, the LE deflection provides about 10% improvement, followed by the combined LE&TE deflections (8%). It is also found that combining various deflections can provide a performance increase over drastically different areas of the range of angle of attack. a _Article_  
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in or on the vehicles, and providing fast and precise navigation and maneuverability. Another goal is to have simplified means for the flow control design to reduce required user input. Leading edge (LE) and trailing edge (TE) deflections of airfoils are strategies that can improve and optimize aerodynamic performance under various conditions occurring during flight. In the case of rotorcraft, the flight conditions take place in an ever-changing flow field, dissimilar to fixed-wing aircraft and when a rotorcraft is flying in straight and level flight. As each rotor turns around the center of the aircraft, it encounters disturbed air from the rotor in front of it. This introduces a problem when it comes to selecting an airfoil that will be optimized for the expected flow conditions, as one airfoil cannot possibly be optimized for every azimuth throughout the blade rotation. The application of a morphing airfoil to rotorcraft can provide a more optimized airfoil shape throughout the entire flow regime under many different flight profiles with minimal pilot input, aimed at optimizing the airfoil shape for better flight characteristics and efficiency. This has been an area of great interest over the years, but as technology advances, these morphing airfoils are coming closer to fruition. This investigation aims to elucidate benefits from various wing deflections during pitching that could be implemented in these morphing strategies. Various methods of shape optimization have been proposed in the literature over the past decades and tested experimentally. In an earlier experimental and numerical work [5,6], a variable droop in the leading edge design produced notable benefits in the helicopter VR-12's airfoil performance. These studies combined the design of a variable leading edge, wind tunnel testing (optical interferometry for density measurements and pressure transducers), and computational fluid dynamics (CFD). Most recently [19,22,23], wind tunnel tests have provided additional datasets confirming the benefits of the designs. For example, the study in Ref. [19] combined a flexible wing surface design with numerical simulations (RANS) and wind tunnel testing (pressure transducers, force balance transducers, and infrared visualizations of transition). The studies in Refs.