3D Computational Studies of Flapping Wing in Frontal Gusty Shear Flow

The present paper reports findings of the 3D computational studies of the effect of frontal gusty shear flow on the force patterns of a flapping wing. A rigid wing with semi-elliptical wing planform with asymmetric 1 DoF flapping kinematics was exposed to a gusty shear flow. The shear gradient of the flow was varied from −10 to +10 in steps of 5. Computation studies were carried out for Re = 150 which lies in the typical flight Reynolds number range of natural flyers like a fruit fly and anthropogenic flyers like a Pico Aerial Vehicle. 3D, unsteady, laminar, and incompressible Navier-Stokes equations were solved using finite volume formulation based commercial code ANSYS Fluent. Wing kinematics and gusty inflow conditions were modelled into the solver by User Defined Functions (UDFs). Wing motion was simulated using the dynamic meshing technique. The effect due to variation in the frontal inflow condition was studied quantitatively and qualitatively. Comparisons of the instantaneous and gust cycle averaged forces and moment coefficients about the wing root mid chord point and 3D phase space projections of the forces and moment coefficients was carried out. Qualitative studies were carried out by comparing the static pressure over both the surfaces of the wing and the vortex patterns near the flapping wing using λ2–criteria. It was observed from these studies that negative shear gradient resulted in a rise in the vertical force and moment and a minor reduction in the horizontal force. Positive shear gradient resulted in a minor rise in horizontal force and a significant reduction in vertical force and moment.