Ceiling effects on the aerodynamics of a flapping wing at hovering condition

The ceiling effect on the aerodynamics of a hovering flapping wing is investigated by solving the three-dimensional incompressible Navier-Stokes equations. Computations have been carried out for some parameters including the distance between the wing and the ceiling, the Reynolds number, the stroke amplitude, and the mid-stroke angle of incidence. The ceiling effect on the force production and vortical structures around the wing is analyzed. It is shown that the ceiling effect increases the aerodynamic forces. This improvement in force production in the ceiling effect is caused by the increments both in the relative velocity of oncoming flow and the effective angle of attack of the wing. The underlying mechanism is that the presence of the ceiling acts as a mirror as if there exists a mirroring leading-edge vortex (LEV). This mirroring LEV not only increases the relative velocity of the oncoming flow ahead of the wing but also produces an upwash to the oncoming flow, hence increasing the effective angle of attack of the wing.