ETD

Archivio digitale delle tesi discusse presso l'Università di Pisa

Tesi etd-06202012-201915


Tipo di tesi
Tesi di laurea specialistica
Autore
TESONE, MARIO
URN
etd-06202012-201915
Titolo
Lagrangian characterization of intrinsic filtering errors in inertial particle tracking in LES flow fields
Dipartimento
INGEGNERIA
Corso di studi
INGEGNERIA AEROSPAZIALE
Relatori
relatore Salvetti, Maria Vittoria
relatore Chibbaro, Sergio
Parole chiave
  • two-phase flows
  • pure filtering error
  • Lagrangian particle tracking
Data inizio appello
10/07/2012
Consultabilità
Non consultabile
Data di rilascio
10/07/2052
Riassunto
Particle transport, dispersion, and segregation in turbulent flows are highly nonuniform and intermittent phenomena which are recognized to depend on the local dynamics of turbulence structures. The dispersion of small inertial particles in inhomogeneous turbulent flows is important in many industrial applications and environmental phenomena, such as, for instance, mixing, combustion, depulveration, spray dynamics, pollutant dispersion or cloud dynamics.
Direct Numerical Simulations (DNS) of turbulence coupled with Lagrangian Particle Tracking (LPT) have shown their capability to capture the mechanisms characterizing particle dynamics in turbulent flows. Because of the computational requirements of DNS the analysis of problems characterized by complex geometries and high Reynolds numbers demands alternative approaches: for instance, Large-Eddy Simulation (LES) is increasingly gaining in popularity, especially for cases where the large flow scales control particle motion.
LES is based on a filtering approach of the fluid phase governing equations in which the unresolved Sub-Grid Scales (SGS) of turbulence must be modeled.
The output of LES is therefeore the filtered velocity field. If particles are tracked in the LES fluid velocity fields, inaccurate predictions of particle dispersion and near-wall accumulation are obtained. Therefore, closure models are needed also in the particle motion equations, in order to reintroduce the effects of the SGS
fluid velocity fluctuations. The quantification and the analysis of the errors present in LPT in LES flow fields is necessary to develop efficient SGS closure models.
In this work we focus on the error purely due to filtering of the fluid velocity field seen by the particles. The aim is to model these effects through a statistical Lagrangian description of the relevant geometrical features of turbulence in the near-wall region, where preferential concentration and accumulation are controlled by structures like sweeps and ejections.
The purpose of this work is to characterize the statistical properties (in terms of PDFs) of the pure filtering error computed along the Lagrangian particle trajectories and conditioned to the initial position of particles. In the first analyzed case, in DNS particles are initially released in three regions of the channel: near the wall, at the channel centerline and in an intermediate region. In a second set of DNS particles are initially released in regions sampling sweep or ejections events. The statistical properties of the particle dynamics in DNS and of the pure filtering error are characterized from a Lagrangian point of view along the particle trajectories for all the considered initial conditions.
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