Study of Aerodynamic and Heat-Exhaust Characteristics for a High-Altitude Long-Endurance Unmanned-Aerial-Vehicle Airfoil

This paper identifies exhaust heat characteristics depending on airfoil shapes at low Reynolds number to design a high-altitude long-endurance unmanned aerial vehicle with a wing-surface heat exchanger. In the first step, computational fluid dynamics simulations are conducted for different airfoils, each of which exhausts heat from different regions on the upper surface, at different angles of attack. This parametric study reveals that early transition near the leading edge is favorable to improve heat-exhaust characteristics, although it may increase skin friction. In addition, heat exhaust should be conducted only in the region of turbulent boundary layer behind the transition point. From these results, the airfoil shape significantly affects the Nusselt-number distribution along the upper wing surface due to the change in the location of laminar-turbulent transition and turbulent boundary-layer separation. In the next step, multi-objective optimization of an airfoil shape, which balances aerodynamic performance and heat-exhaust performance, is carried out. The obtained nondominated solutions show the tradeoffs between aerodynamic performance and heat-exhaust performance. It was confirmed that heat-exhaust performance can be controlled by the location of the laminar-turbulent transition, and improved without sacrificing aerodynamic performance at the cruising condition.