Experimental investigation of the fluttering flag using FSI-POD

Fluttering flag exhibit complex behavior due to the continuous energy exchange between a deforming structure and a flowing fluid. Fluid-structure interaction-proper orthogonal decomposition (FSI-POD) was proposed by Goza & Colonius [JF&S:2018], and they successfully applied it to a computational flag FSI studies. One benefit of using FSI-POD is that it couples the fluid and structure energy together, elucidating the interplay between the fluid and structure observed in FSI problems. This study focuses on developing FSI-POD for the experimental investigation of a fluttering flag. For this purpose, particle image velocimetry (PIV) measurements were performed on the flag fluttering in an open jet. The flag had a mass ratio of 1.47, an aspect ratio of 0.25, a dimensionless rigidity of , and a Reynolds number based on flag length is . The raw PIV images were used to estimate the position and velocity of the structure using an algorithm developed in-house. The position and velocity of the flag allowed for the estimation of the energy of the structure required for the FSI-POD implementation. The velocity flow field data were obtained using the traditional PIV cross-correlation technique. These results showed it is possible to implement FSI-POD for fluttering flags using only the PIV measurements. Additionally, the results highlight the complex energy exchange between the fluid and flag during limit-cycle oscillation, which would not have been possible otherwise.