Aerodynamic Characteristics of a Tandem Flapping Wing in Inclined Stroke Plane Hovering with Ground Effect

The present two-dimensional study investigates the ground effect on the aerodynamic characteristics of a tandem flapping wing in inclined stroke plane hovering using ANSYS Fluent. The role of various wing kinematics parameters (flapping frequency f, stroke amplitude A_o/c, and phase difference ψ = 0° and 180°), in combination with ground distance (D* = D/c), is studied. The results reveal that a large stroke amplitude A_o/c decreases vertical force generation for both in-phase and counter-stroking patterns. The vertical force notably increases for both in-phase and counter-stroking wings when D* is extremely small (D* = 0.5). A maximum vertical force enhancement of approximately 65% and 35% is observed for in-phase and counter-stroking patterns, respectively, at D* = 0.5. This enhancement is primarily attributed to the strengthening of detached vortices on the lower surface of the wings during the middle of the downstroke when flapping at extremely small ground distances. In addition, the wing-wing interaction and secondary rebound vortex, caused by wing-ground interaction, also play a key role in vertical force generation. The wing-ground interaction positively influences both vertical and thrust force generation for in-phase and counter-stroking wings at small ground distances. In general, the vertical and thrust forces generated by in-phase stroking wings are greater than those produced by counter-stroking wings.