Spectral proper orthogonal decomposition and resolvent analysis of near-wall coherent structures in turbulent pipe flows

• DOI: 10.1017/jfm.2020.445
• Publication Date: 2020-08-12T13:26:38Z
• Authors: Leandra I. Abreu; André V. G. Caval...; Philipp Schlatter; Ricardo Vinuesa; Dan S. Henningson
• Keywords: Proper orthogonal decomposition; Lagrangian Coherent Structures

Direct numerical simulations, performed with a high-order spectral-element method, are used to study coherent structures in turbulent pipe flow at friction Reynolds numbers $Re_{\tau} = 180$ and $550$. The database was analysed using spectral proper orthogonal decomposition (SPOD) identify energetically dominant structures, most of which turn out be streaks quasi-streamwise vortices. To understand how such can modelled, the linear responses harmonic forcing were computed singular value resolvent operator, mean field as base flow. SPOD analysis calculated for several combinations frequencies wavenumbers, allowing map similarities between modes optimal wide range relevant scales flows. In order explore physical reasons behind agreement both methods, an indicator lift-up mechanism introduced, activated when represents vortices associated response corresponds streaks. Good leading is observed large region parameter space. this region, significant gain separation found analysis, may attributed strong amplification mechanism. For numbers, concordances generally energy buffer layer. results highlight pertinent reduced-order model wall-bounded turbulence, particularly streamwise elongated corresponding near-wall