A Comparative Modal Analysis of the Interaction of Flow with Tandem Cylinders

Modal decomposition techniques are widely employed to analyze turbulent flows by identify- ing coherent structures, which are often linked to key flow features, such as unsteady loading and pressure fluctuations. Modal decomposition offers a powerful framework for uncovering these structures and interpreting their role in flow dynamics. The most popular methods include POD (proper orthogonal decomposition), SPOD (spectral proper orthogonal decomposition), and DMD (dynamic mode decomposition). In this paper, we explore the flow interaction with tandem cylinders arranged in a bi-stable configuration. The velocity field, unsteady surface pressure, and far-field acoustic pressure of a tandem cylinder configuration are measured simultaneously using a high-speed PIV system, a remote microphone technique, and a far-field microphone, respectively. We utilize POD, SPOD and kEDMD (kernelized extended DMD) to identify coherent structures in the vorticity field. These three methods are compared to relate the vertical structures associated with the key flow regimes to surface and far-field pressure measurements. Results show that POD and SPOD offer insight into the important frequencies in an efficient manner, whilst the versatility of DMD-based methods offers further clarity into the dynamics of the system via the Koopman modes.