Two-and three-dimensional low-aspect-ratio (AR 4) hovering airfoil/wing aerodynamics at a low Reynolds number (Re 100) are numerically investigated. Regarding fluid physics, in addition to the well-known leading-edge vortex and wake-capture mechanisms, a persistent jet, induced by the shed vortices in the wake during previous strokes, and tip vortices can significantly influence the lift and power performance. While in classical stationary wing theory the tip vortices are seen as wasted energy, here, they can interact with the leading-edge vortex to contribute to the lift generated without increasing the power requirements. Using surrogate modeling techniques, the two-and three-dimensional time-averaged aerodynamic forces were predicted well over a large range of kinematic motions when compared with the Navier-Stokes solutions. The combined effects of tip vortices, leading-edge vortex, and jet can be manipulated by the choice of kinematics to make a three-dimensional wing aerodynamically better or worse than an infinitely long wing. The environmental sensitivity during hovering for select kinematics is also examined. Different freestream strengths and orientations are imposed, with the impact on vortex generation and wake interaction investigated.

Flapping wing MAV aerodynamics is challenging to understand due to its complexities. Surrogate modeling offers an effective tool to predict information at off-design points, measure the sensitivity of design variables involved, and illustrate general trends in the data. We have investigated 2D and 3D hovering airfoil/wing aerodynamics considering three kinematic parameters, i.e. plunge amplitude, angular amplitude, and phase lag, at Re = 100. While leading edge vortex, a persistent downward jet, and wake capture are three noticeable fluid dynamics features in 2D and 3D, tip vortices in 3D and instantaneous AoA can substantially affect the relative importance of them. Surrogate models of the 2D and 3D wing with aspect ratio of 4 show that for i) power required, the magnitudes and global trends of the predicted response between 2D and 3D are similar, ii) lift, the phase lag changes from a non-linear response in 2D to a monotonic one in 3D. The overall consequence is that in 3D, kinematic combinations of higher lift with lower power requirements can be attained. Global sensitivity analysis shows that the lift is the most sensitive to the phase lag in 3D as opposed to the angular amplitude in 2D. The ensemble surrogate strategies performed employed performed quite well compared to independent test data.

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Two-and three-dimensional, low aspect ratio (AR=4), hovering airfoil/wing aerodynamics at low Reynolds number (Re = 100) are numerically investigated. Regarding fluid physics, in addition to the well-known leading edge vortex and wake-capture mechanisms, a persistent jet, induced by the shed vortices in the wake during previous strokes, and tip vortices can significantly influence the lift and power performance. While in classical stationary wing theory the tip vortices are seen as wasted energy, here, they can interact with the leading edge vortex to contribute to the lift generated without increasing the power requirements. Using surrogate modeling techniques, the two-and three-dimensional time averaged aerodynamic forces were predicted well over a large range of kinematic motions when compared to the Navier-Stokes solutions. The combined effects of tip vortices, leading edge vortex, and jet can be manipulated by the choice of kinematics to make a three-dimensional wing aerodynamically better or worse than an infinitely long wing. The environmental sensitivity during hovering for select kinematics is also examined. Different freestream strengths and orientations are imposed with the impact on vortex generation and wake interaction investigated with implications on the applicability of quasi-steady models.