Spectral decomposition of the turbulent self-similar jet and recomposition using linear dynamics

Coherent structures in the far field of a round turbulent jet at exit Reynolds number Re = 17 000 are investigated experimentally by means of time-resolved 2D-3C PIV in stream-wise and cross-stream sections of the flow. Empirical mode shapes are extracted via spectral proper orthogonal decomposition and the results are compared to two modelling approaches. A local quasi-parallel stability analysis is carried out based on the self-similar velocity profiles and a global optimal response analysis is performed. For both analyses, an eddy viscosity model is employed. The results of both models compare well with the experiments for azimuthal wavenumbers m = 0 to m = ±3 over a wide frequency range. In particular, the optimal response modes show an excellent agreement of up to 98% with the empirical modes, even representing dynamics in the inertial subrange. Within the resolvent framework, non-modal effects are indirectly accounted for and the non-parallelism of the flow does not constitute a restriction to the results as opposed to the quasi-parallel analysis which shows an agreement of up to 95% with the experiments.