Scalable Energy Harvesting via Lift Control in Taylor-Green Flows

We explore how simple lift control strategies enable unpowered flight vehicles to extract energy from spatially structured winds. To generalize these results, we derive dimensionless equations of motion that depend on a controllable lift coefficient, the optimal glide ratio, and two dimensionless parameters, the glider Stokes number, which characterizes the vehicle responsiveness to the flow, and the glider settling parameter, which captures the balance between gravity and lift. Using a two-dimensional Taylor-Green vortex field, we simulate the motion of gliders across a range of glider Stokes numbers. We evaluate the performance of a fixed-lift coefficient controller and compare it to a greedy controller that prioritizes lift inputs that improve forward progress and altitude gain. We find that the greedy controller consistently outperforms the fixed-lift coefficient case, resulting in higher speeds and, in some cases, shallower descent angles. The effectiveness of the controller depends on the interplay between the flow and the vehicle inertia. These results provide insight into scalable energy harvesting mechanisms for small aerial vehicles operating in unsteady environments.