Study of two-element airfoils for long endurance flight at low reynolds numbers

Unmanned Aerial Vehicles (UAVs) are highly effective platforms for surveillance, remote sensing, search and rescue operations and other missions requiring demanding long endurance. Small scale UAVs normally operate at the low Reynolds numbers, where laminar separation bubbles are observed. These bubbles severely limit performance by inhibiting lift and increasing drag, thus decreasing the endurance factor. Two-element airfoils address these difficulties by re-energizing the boundary layer to mitigate the ill-effects of laminar separation bubbles or flow separation, achieving high lift and low drag. We aim to investigate if two-element airfoils can improve the endurance factor over their single element counterparts. Airfoils evolved from Wortmann FX63-137 with high thickness (18%) were studied using the four-equation γ-Re-θ or Transition SST model implemented in ANSYS FLUENT. This leads to new insights in designing two-element airfoils for long endurance UAVs operating in the low Reynold number regime, which are largely missing in literature.