Decomposition of wake dynamics in fluid-structure interaction via low-dimensional models

We present a dynamic decomposition analysis of wake flow in fluid-structure interaction (FSI) systems under both laminar and turbulent flow conditions. Of particular interest is to present the interaction dynamics of low-dimensional features to sustain the free vibration of a low mass ratio square cylinder. The snapshot data from high-dimensional FSI simulations are projected to a low-dimensional subspace using the proper orthogonal decomposition (POD). We utilize the corresponding POD modes to detect features e.g. vortex street, shear layer and near-wake bubble. The vortex shedding modes contribute solely to the lift force while the near-wake and shear layer modes contribute to the drag force. We ascertain quantitatively that the shear layer feeds vorticity flux to the wake vortices and the near-wake bubble during wake-body synchronization. We propose an interaction cycle to provide the inter-relationship between high amplitude motion and wake features. This wake-synchronization cycle is also found to be valid for turbulent wake flow. We discover that, for below critical Re flows the bluff body undergoes a high-amplitude vibration due to flexibility-induced unsteadiness.