Capturing the dynamical transitions in the flow-field of a flapping foil using Immersed Boundary Method

The present work investigates the underlying flow physics behind dynamical transitions that take place in the flow-field around a plunging foil as the nondimensional plunge velocity (κh) is increased. The unsteady flow-field is seen to undergo a transition from periodicity to chaos through a quasi-periodic route. Numerical simulations have been performed at different parametric regimes associated with the different dynamical states, using an in-house flow solver developed based on discrete forcing type Immersed Boundary Method (IBM). Results obtained using the IBM methodology are compared both qualitatively and quantitatively with those from a well-validated body-fitted Arbitrary Lagrangian-Eulerian (ALE) approach. This study explores the scope of body non-conformal mesh methods in comparison to body fitted approaches in capturing complex flow topologies, especially, during aperiodic flow regimes. In the discrete direct forcing type IBM solver developed in the present study, application of the momentum forcing and mass/source sink terms at all the grid points inside the solid domain is seen to capture various unsteady flow-mechanisms accurately. These mechanisms are crucial in dictating the dynamics and they play key roles in triggering the aperiodic onsets and sustaining them.