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Effect of LES closures on the entrainment of a passive scalar in a turbulent planar jet

DOI: 10.1615/ICHMT.2012.ProcSevIntSympTurbHeatTransfPal.1660
pages 1615-1623

D. C. Lopes
Technical University of Lisbon, Instituto Superior Técnico, AV. Rovisco Pais, 1 - 1049-001, Lisboa, Portugal

Carlos B. da Silva
Department of Mechanical Engineering (DEM) IDMEC/IST, Technical University of Lisbon Av. Rovisco Pais, 1049-001 Lisbon, Portugal

Ricardo J. N. dos Reis
Mechanical Engineering Department Instituto Superior Tecnico Av. Rovisco Pais, 1049-001 Lisboa Portugal

Venkatramanan Raman
University of Texas at Austin, W. R. Woolrich Laboratories, 210 East 24th Street, Austin, Texas 78712-0235, USA

Sinopsis

Classical large-eddy simulation (LES) modelling assumes that the subgrid-scale (SGS) models do not influence large scale quantities, even though there is by now ample evidence of this influence in many flows. In this work we focus on the effect of SGS models on integral quantities as obtained in the simulation of turbulent jets with passive scalars, such as the velocity and scalar spreading and centreline decay rates. Detailed analysis of the thin layer bounding the turbulent and non-turbulent regions (the so called turbulent/non-turbulent interface) shows that this region raises challenges for classical subgrid-scale models. The small scales are very far from equilibrium and contain an high fraction of the total energy. The situation is worse for the scalar than for the velocity field. Large-eddy simulations (LES) of turbulent planar jets are used to show the effect of several subgrid-scale models in the integral quantities of planar jets e.g. spreading and centreline decay rates. Finally, the results suggest the existence of a critical resolution of the order of the Taylor scale for the scalar field i.e. coarser passive scalar LES above this limit results in dramatic changes in the integral quantities. This result is linked with the dynamics of the small scales near the jet interface analysed before.

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