On the stabilization of the leading edge vortex of an auto-rotating winged seed

Direct numerical simulations of the auto-rotation of a winged-seed model are performed at Reynolds number between 80 and 240. The simulations are performed by coupling the Navier-Stokes equations with the Newton-Euler equations of the seed. Due to this coupling, the flow around the seed and the kinematics of the seed change with Re. In particular, as the Reynolds number increases, the coning angle decreases and the angular velocity of the seed increases. In terms of the flow characterization, it is observed that a stable leading edge vortex (LEV) develops on the upper surface of the wing of the auto-rotating seed, in accordance to existing literature. Using a reference frame attached to the seed, the effect of the Reynolds number in the relative velocity, relative vorticity and pressure is analyzed. Three possible stabilization mechanisms for the LEV are evaluated (i.e., Coriolis/centrifugal accelerations, vorticity transport along the LEV and viscous effects). The results suggest that, for the present geometry and range of Reynolds number, only the effect of Coriolis/centrifugal accelerations is relevant in the stabilization of the LEV.