Application of Proper Orthogonal Decomposition to Study the Flow Over an Oscillating Flag

Abstract

Abstract Fluid-Structure-Interaction (FSI) is the coupling between a flowing fluid and a structure that results in either a static or dynamic structure deformation. This investigation focused on applying Proper Orthogonal Decomposition (POD) to study the fluid flow behavior of an oscillating flag and using POD modes to quantify the changes in flow behavior associated with the change in flag oscillation modes. For this purpose, aerodynamic load, membrane location, and Particle Image Velocimetry (PIV) measurements were performed for a selected flag model. The flag location measurements helped identify the change in oscillation shapes and modes with change in flow conditions, while the aerodynamic load data allowed us to quantify the impact of flag oscillations on the aerodynamic load experienced by the flag. The PIV data provide flow field information around the oscillating flag and were used to perform POD analysis. We observed that the POD mode, energy, and time-varying coefficients changed with change in the oscillation modes of the flag (i.e., change from mode-2 to mode-3 oscillations). Flow reconstruction using the first three POD modes allowed us to capture changes generated in large-scale structures in the flow due to changes in the oscillation modes. Flow reconstruction using the remaining POD modes allowed us to observe the behavior of small-scale flow structures and K-H vortices in the wake of the flag. The POD approach used here allowed us to quantify the change in flow behavior and understand the underlying FSI mechanism therein.