English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Response modes computed via linear resolvent analysis of a turbulentmean-flow field have been shown to qualitatively capture characteristics of theobserved turbulent coherent structures in both wall-bounded and free shearflows. To make such resolvent models predictive, the nonlinear forcing termmust be closed. Strategies to do so include imposing self-consistent sets oftriadic interactions, proposing various source models, or through turbulencemodelling. For the latter, several investigators have proposed using themean-field eddy viscosity acting linearly on the fluctuation field. In thisstudy, a data-driven approach is taken to quantitatively improve linearresolvent models by deducing an optimal eddy-viscosity field that maximizes theprojection of the dominant resolvent mode to the energy-optimal coherentstructure educed using spectral proper orthogonal decomposition (SPOD) of datafrom high-fidelity simulations. We use large-eddy simulation databases forround isothermal jets at subsonic, transonic, and supersonic conditions andshow that the optimal eddy viscosity substantially improves the alignmentbetween resolvent and SPOD modes, reaching over 90% alignment at thosefrequencies where the jet exhibits a low-rank response. We then consider afixed model for the eddy viscosity and show that with the calibration of asingle constant, the results are generally close to the optimal one. Inparticular, the use of a standard Reynolds-Averaged-Navier-Stokes (RANS)eddy-viscosity resolvent model, with a single coefficient, provides substantialagreement between SPOD and resolvent modes for three turbulent jets and acrossthe most energetic wavenumbers and frequencies.

Optimal eddy viscosity for resolvent-based models of coherent structures in turbulent jets