Optimal frequency resolution for spectral proper orthogonal decomposition

Abstract

We demonstrate that accurate computation of the spectral proper orthogonal decomposition (SPOD) critically depends on the choice of frequency resolution. Using both artificially generated data and large-eddy simulation data of a turbulent subsonic jet, we show that the optimal choice depends on how rapidly the SPOD modes change in space at adjacent frequencies. Previously employed values are found to be too high, resulting in unnecessarily biased results at physically important frequencies. A physics-informed adaptive frequency-resolution SPOD algorithm is developed that provides substantially less biased SPOD modes than the standard constant resolution method.