Spectral kinetic energy budget in bubble swarm with DNS and Front-Tracking method
Résumé
A close look at the interaction between bubble-induced agitation and a turbulent flow forced at large scalesis necessary to identify the key mechanism at play in the kinetic energy budget1. It is of an especially stronginterest for the Euler-Euler two-fluid RANS modeling to correctly capture the level of turbulent kinetic energyin the flow as its value is used as an input in other models. Several models with more or less complexity havebeen proposed with, for instance, an additional source terms in two-equations models or Reynolds-stress-basedmodels. However, all these models still lack a proper breakdown of the mechanisms by which fluctuations areproduced.To disentangle the origin and effect of those fluctuations and improve modeling, we performed numericalsimulations of bubbly flows using a one-fluid Navier-Stokes solver and a front-tracking method in a tripleperiodicdomain. To produce turbulent bubbly flow, a large-scale forcing is added to the swarm simulations.Our objective is to characterise the scale-by-scale interaction between fluctuations. Three volume fractions arestudied ([3, 6, 12]%) with a forcing equivalent to a Reλ = 150 flow. A precise parametrisation allows to placethe bubble diameter at the bottom of the inertial range of the single-phase flow enabling a direct interaction.The probability density function (PDF) of vertical velocity on Figure 1a shows that liquid velocity fluctuationsin the coupled simulation (HIT, 3 %) is almost identical to the single phase forced simulation (HIT).The significant asymmetry of the bubbles-only simulation (3 %) is wiped by the forcing. But thescale-by-scale budget shows that the spectral signature of the bubbles still plays a major role in the dynamics ofthe fluctuations.After detailing the simulation definition and post-processing procedure4, those results will be discussed withan emphasis on the RANS modeling consequences.
Fichier principal
Spectral_analysis_of_a_forced_turbulent_bubbly_flow.pdf (116.55 Ko)
Télécharger le fichier
Origine | Fichiers produits par l'(les) auteur(s) |
---|