Distributed electric propulsion slipstream aerodynamic effects at low Reynolds number

Based on the research of the high altitude long endurance (HALE) solar-powered unmanned aerial vehicles (UAVs), the low Reynolds aerodynamic properties of three different propeller-wing configurations are numerically simulated by quasi-steadily solving the Reynolds averaged Navier-Stokes (RANS) equations of multiple reference frames (MRF) based on the hybrid grid technology and k-k_L-ω transition model. Under the request of equal thrust, the distributed electric propulsion (DEP) slipstream effects on the FX 63-137 wing are analyzed by the comparison of the aerodynamic forces and flow characteristics between different configurations. It shows that the application of DEP is supposed to improve the lift property but to worsen the drag property heavily, which is mainly due to the increase of the flow speed and total pressure; the propeller slipstream helps expand the area of turbulent adherent flow by bringing turbulent energy into the boundary layer to sustain strong adverse pressure gradient; the appearance of vortex structures at the boundaries of slipstream regions indicates that multiple propellers' slipstream regions strongly interact with the flow field on the wing at low Reynolds numbers.