Unsteady Aerodynamics and Aeroelastic Control of a Fixed-Wing UAV with Shark-skin Inspired Micropillars

Unmanned aerial vehicles (UAVs), particularly small fixed-wing designs, often operate in low Reynolds number regimes, leading to transitional flow separation. Flow-induced vibrations affect performance, stability, and structural integrity, making flow control a critical area of study. This research investigates the aerodynamic effectiveness of bio-inspired sharkskin coatings on a small fixed-wing UAV, the "Switchblade”. The bioinspired coatings consisting of uniformly distributed cylindrical micropillars (70 μm and 140 μm) with diverging-tip structures were applied to the upper wing surface. Wind tunnel experiments were conducted at Texas Tech University’s National Wind Institute, with cruise speeds of 17 m/s and 30 m/s, corresponding to Reynolds numbers based on mean aerodynamic chord of 2.1×105 and 3.7×105, respectively. Static angles of attack ranged from 10° to 17°, with a focus on the stall region. Aerodynamic performance was assessed using load cell measurements for lift and drag forces, along with wing displacement data obtained through laser displacement sensors. High-speed camera imaging was used to capture aerodynamic forces and structural response for both coated and uncoated experimental cases. Additionally, phase-locked Laser Doppler Velocimetry (LDV) measured streamwise flow at 13° and 15° (stall angles) at two different spanwise locations (the midspan and the tip of the wing) for three different chordwise locations (the leading edge, mid-chord and trailing edge) on the UAV wing. Results indicate that bio-inspired micropillars effectively reduce flow separation and associated vibrations, improving aerodynamic performance at high angles of attack when properly implemented on small fixed-wing UAVs.