Spectral analysis of turbulence in jets
Oliver Schmidt and coauthors posted a new paper on arXiv on spectral analysis of jet turbulence. Data from several LES (computed at Cascade Technologies) across a range of Mech numbers was examined using spectral POD. The data highlight that, from a global point of view, there are frequency/azimuthal-mode regimes where the jet exhibits either low-rank or non-low-rank behavior. The low rank structures are Kelvin-Helmholtz wavepackets that have been observed in past and previously modeled with parabolized stability equations. The non-low-rank behavior is associated with Orr-like wavepackets which dominate the downstream, fully developed jet and, as suboptimal modes, exist also in the potential core region. The work helps explain previous successes and failures at modeling structures in jets, and points to resolvent-based models for future progress.