Comparing SPOD and POD for Wake Flow of Tandem Oscillating Cylinders

Spectral Proper Orthogonal Decomposition (SPOD) is the form of proper orthogonal decomposition performed in the frequency domain. It is capable of sifting frequency contents from large data sets and preserving and revealing structures dependent on frequency. Proper Orthogonal Decomposition (POD) is a highly versatile and popular reduced order method that can quickly find structures in flow data. In this study, SPOD and POD analyses are performed on simulated flow around tandem oscillating cylinders to compare the effectiveness of both methods. Reconstructions are performed using select SPOD and POD modes of the spectral data to observe the ability of each method to preserve important flow structures and physics. SPOD is shown to be more effective at extracting smaller flow structures of which POD is likely to mix with larger structures, creating distortions. The reconstructed flow is shown to preserve important structures in the time domain which demonstrates that extraction of flow structures using either POD or SPOD can be properly mapped back to the physical domain.