Dynamics of sedimentation of flexible fibers in moderate Reynolds number flows

Direct simulations of dynamics of free falling of single and multi flexible cylindrical fibers in a finite Reynolds number flow are performed. Fiber flexibility and unsteady fluid dynamics are treated as a coupled system, utilizing a lattice Boltzmann (LB) equation and a flexible structure model. Effects of flexibility on unsteady dynamics are studied. It is demonstrated that not only flexible single fiber but also multi flexible diluted fibers have a larger settling velocity than stiff fibers. More streamlined fiber shape due to flexibility significantly reduces drag forces. It is shown that multi-fibers have a larger settling velocity than its corresponding single isolated fiber. It seems that diluted flexible fibers are flocculated more easily than stiff fibers.