Numerical Investigation of Coupled-Attitude Aerodynamic Characteristics of a Frigatebird-Inspired Wing in Marine Atmospheric Updrafts

Frigatebirds achieve exceptional long-endurance flight by efficiently utilizing marine atmospheric updrafts, offering a valuable biological prototype for low-energy bionic aircraft. Most existing studies focus on uniform inflow and single-axis attitudes, lacking systematic analysis of coupled-attitude aerodynamics and flow-field mechanisms in updraft environments. This work numerically investigates both clean-wing and fuselage-equipped frigatebird-inspired configurations under pitch-alone, pitch–yaw coupled, and yaw–roll coupled attitudes using the RANS/k-ω SST method. Results show that updraft effects exhibit strong pitch-angle dependence: significant drag reduction (maximum 0.0984) and lift augmentation occur within −12∘<α<4∘, while above α=4∘ updrafts suppress full-span deep stall and extend the stall angle by more than 8∘, with a maximum lift increment of 220% near the wingtip. Under pitch–yaw coupling, a high-efficiency aerodynamic window emerges with a physically meaningful peak lift-to-drag ratio of 9.55. For yaw–roll coupling, the rolling moment is fundamentally driven by sideslip-induced asymmetric separation bubbles rather than by roll angle itself, as confirmed by surface limiting streamlines, skin friction distributions, and velocity vector plots. The bionic wing also achieves a near-elliptical spanwise lift distribution with an Oswald efficiency of approximately 0.994. This study provides key support for aerodynamic design, attitude control, and updraft energy harvesting of bird-like aerial vehicles.