Aero-propulsive integration effects of an overwing distributed electric propulsion system

A series of experiments were conducted on a quasi-2D S8036 airfoil with a distributed electric propulsion (DEP) system. An overwing ducted fan system was tested with varied thrust angles achieved by deflecting the fan exit flow direction. The DEP system was comprised of five electric fans mounted on the upper surface of the airfoil trailing edge. The electric ducted fans were sized with a diameter-to-chord ratio of 19.7%, and five fans were installed to cover 70.3% of the airfoil model span. Aerodynamic forces and moments were recorded for the airfoil in a static condition, as well as across a range of Reynolds numbers, angles of attack, tip speed ratios, and nozzle deflection angles. It was found that nozzle deflection led to a significant increase in the stream-normal force due to an increase in circulation-based lift and direct thrust force. At low thrust deflection angles, increases in stream-normal forces were also observed, alongside significant amounts of forward thrust, with increased fan tip speed ratio. At a given nozzle defleciton angle and fan tip speed ratio, minimal variations in pressure distributions were found across the spanwise region covered by the center-fan radius, suggesting a reasonably spanwise-invariant loading produced by the installation of the overwing ducted fan DEP system. Thrust vectoring was also observed to increase the magnitude of the overall pitching moment, and this effect was significantly amplified by the tip speed ratio of the fans. These observations were attributed to the role of the vectored nozzle system in producing a jet-flap system, with varying induced circulation effects brought about by control of the nozzle deflection angle and the fan tip speed ratio.