Chronos-Koopman spectral analysis of bidimensional turbulent flows

We undertake a spectral analysis of a turbulent flow in a soap film using a Chronos-Koopman (CK) technique. The approach enables us to extract modes corresponding to spatial structures evolving with a single frequency, quantify their associated energy, and identify energy transfer mechanisms compatible with an inverse energy and a direct enstrophy cascade. We link the kinematic coupling between modes with sweeping associated with the mean flow. Inspection of eigenvalue maps of the CK decomposition does not show evidence of any significant amplifying or evanescent modes, suggesting negligible or the absence of on–off intermittency and spatial inhomogeneities in the case under study.