Zeren, Zafer. Lagrangian stochastic modeling of turbulent gassolid flows with twoway coupling in homogeneous isotropic turbulence. PhD, Institut National Polytechnique de Toulouse, 2010

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Official URL: http://ethesis.inptoulouse.fr/archive/00001478/
Abstract
In this thesis, performed in IMFT, we are interested in the turbulent gassolid flows and more specifically, in the phenomenon of turbulence modulation which is the modification of the structure of the turbulence due to the solid particles. This mechanism is crucial in flows with high particle massloadings. In this work, we considered a homogeneous isotropic turbulence without gravity kept stationary with stochastic type forcing. Discrete particles are tracked individually in Lagrangian manner. Turbulence of the carrier phase is obtained by using DNS. The particles are spherical, rigid and of a diameter smaller than the smallest scales of turbulence. Their density is very large in comparison to the density of the fluid. In this configuration the only force acting on the particles is the drag force. Volume fraction of particles is very small and interparticle interactions are not considered. To model this type of flow, a stochastic approach is used where the fluid element accel eration is modeled using stochastic Langevin equation. The originality in this work is an additional term in the stochastic equation which integrates the effect of the particles on the trajectory of fluid elements. To model this term, we proposed two types of modeling: a mean drag model which is defined using the mean velocities from the mean transport equations of the both phases and an instantaneous drag term which is written with the help of the Mesoscopic Eulerian Approach. The closure of the models is based on the Lagrangian auto correlation function of the fluid velocity and on the transport equation of the fluid kinetic energies. The models are tested in terms of the fluidparticle correlations and fluidparticle turbulent drift velocity. The results show that the mean model, simple, takes into account the principal physical mechanism of turbulence modulation. However, practical closure problem is brought forward to the Lagrangian integral scale and the fluid kinetic energy of the fluid turbulence viewed by the particles.
Item Type:  PhD Thesis 

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Institution:  Université de Toulouse > Institut National Polytechnique de Toulouse  INPT 
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Research Director:  Simonin, Olivier and Bédat, Benoît 
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