Chronos-Koopman spectral analysis of bidimensional turbulent flows

AULIEL, M.I.; CAMMILLERI, A.; MININNI, P. D. ; ARTANA, G. O

Sao Jose dos Campos

Congreso; 10th ABCM Spring School on Transition and Turbulence; 2016

Associacao Brasileira de Ciencias Mecanicas, ABCM

We undertake a spectral analysis of a turbulent flow in a soap film using a Chronos-Koopman (CK) technique. Compared to the usual Eulerian spectral analysis based on the Fourier transform, the CK decomposition has multiple advantages: the flow is decomposed into an empirical basis, it does not require a steady state of velocity fluctuations, it can handle signals with temporal localized events, and the mean kinetic energy can be obtained from the statistics of well defined spatial structures. The methodology is applied to a dataset stemming from a soap film experiment. This approach enables us to identify modes corresponding to spatial structures evolving with a single frequency, their associated energy, and energy transfer mechanisms compatible with an inverse energy and a direct enstrophy cascade, as well as kinematic couplings within modes associated with sweeping by 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 absent intermittencyin the case under study.