Posts

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.
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Spectral POD

Aaron Towne et al. have posted a new paper on spectral proper orthogonal decomposition (SPOD) on arXiv .   SPOD refers to space-time POD modes in a statistically stationary process, which can be readily estimated from the eigensystem of the cross-spectral-density matrix (in frequency space).  This form of POD goes back to the early work of John Lumley, Bill George, Joel Delville, Mark Glauser and other researchers, but has been largely overshadowed by 'snapshot' POD modes based on a space-only decomposition.  The paper derives both old and new results about SPOD, and highlights some nice properties of SPOD including a close relation with DMD, Koopman modes, and resolvent analysis.
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Welcome Dr. Kevin Schmidmayer

Welcome Kevin Schmidmayer to the CFPG! Kevin is a new postdoc who will be working on simulating cavitating flow in both engineering and medical applications. He recently received his PhD from Aix-Marseille Universite, where he studied numerical methods for compressible multicomponent flows, and adaptive mesh refinement.
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Welcome Dr. Erick Salcedo

Join me in welcoming Erick Salcedo to Caltech!  Erick is joining our group after completing his PhD at the National Autonomous University of Mexico.  Erick studied mixed convection in flow around circular cylinders for his PhD using both numerical simulations and experiments.  He is joining the CFPG group to work on the flow energy harvesting project.
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Congratulations *Dr* Goza!

Congratulations to Dr. Andres Goza, who successfully defended his thesis today!  Andres made important contributions to algorithms for flow-structure interaction, and used them to study the regimes of oscillation of so-called 'inverted flags'. Andres is joining Princeton University as a postdoc in Prof. Clancy Rowley's group. We will miss him, but wish him the best in his new job!
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