Influence of ground and ceiling effect on the aerodynamic characteristics of flapping wings

Flapping wing vehicles offer several advantages due to their agility and capacity to manoeuvre through tight spaces. While many studies have investigated the performance of flapping wings near surfaces such as the ground, their interaction with ceiling remains underexplored. Here, we experimentally compared the aerodynamic characteristics of flapping wings operating in close proximity to the ground and ceiling respectively. Experiments were performed using a dynamically-scaled flapping wing apparatus at Re = 3600. At clearances relative to wing-chord of h/c < 1, both ground and ceiling caused an increase in both lift and drag force but, the ceiling had a significantly larger effect on the mean and instantaneous forces over the wing. At lower clearances to the ceiling (h/c < 0.2), the wing produced over 50% more lift and drag compared to that in free hover condition, while the lift to drag ratio remained unchanged. Examining the stroke-phase averaged forces revealed a peak in aerodynamic forces during the early stages of the stroke when the wings was at h/c < 0.3 to ceiling. Analyses of the flow features over the wing during the stroke at h/c < 1 to ground and ceiling revealed that the underlying flow profile between the two conditions maybe significantly different.