Unsteady Aerodynamics And Nonlinear Dynamics Of Free-Falling Rotating Seeds

This work presents a three-dimensional numerical tool that is suitable for studying the aerodynamics and nonlinear dynamics of free-falling rotating seeds like samaras. The proposed simulation framework consists of a modified version of the unsteady vortex-lattice method (enhanced by including a diffusion model and the leading-edge vortex contribution by means of the Polhamus analogy) coupled with a multibody rigid dynamic model for the whole seed. The numerical scheme adopted by the aerodynamic subsystem is based on an explicit low-order integrator (Euler's explicit first-order method). On the other hand, the equations of motion associated with the structural part are integrated in the time domain using a second-order Lie group integrator based on an extension of the classical generalized-a method for dynamical systems. Among the main results obtained, it is found that the predicted terminal descending velocity and angular velocity (around the vertical axis) are in close agreement with experimental results reported in the literature.