4,636 research outputs found
An algebraic-closure-based momentmethod for unsteady Eulerian modeling of non-isothermal particle-laden turbulent flows in very dilute regime and high Stokes number
An algebraic-closure-based moment method (ACBMM) is developed for unsteady Eulerian particle simulations coupled with direct numerical simulations (DNS) of non-isothermal fluid turbulent flows, in very dilute regime and for large Stokes numbers. It is based on a conditional statistical approach which provides a local instantaneous characterization of the dynamic of the dispersed phase accounting for the effect of crossing between particle trajectories which occurs for large Stokes numbers
Fully coupled simulations of monodisperse and bidisperse suspensions in a linear shear flow
The dynamics of macroscopically homogenous sheared suspensions of neutrally buoyant, non-Brownian spheres is investigated in the limit of very small Reynolds and Stokes numbers using the Force Coupling Model (Lomholt & Maxey1). In this numerical approach, the velocity disturbance is obtained by a low order multipole expansion (particle forcing on the flow is represented by monopole and dipole terms spread on a finite volume envelop related to particle radius)
NEPTUNE_CFD High Parallel Computing Performances for Particle-Laden Reactive Flows
This paper presents high performance computing of NEPTUNE_CFD V1.07@Tlse. NEPTUNE_CFD is an unstructured
parallelized code (MPI) using unsteady Eulerian multi-fluid approach for dilute and dense particle-laden reactive
flows. Three-dimensional numerical simulations of two test cases have been carried out. The first one, a uniform
granular shear flow exhibits an excellent scalability of NEPTUNE_CFD up to 1024 cores, and demonstrates the
good agreement between the parallel simulation results and the analytical solutions. Strong scaling and weak scaling
benchmarks have been performed. The second test case, a realistic dense fluidized bed shows the code computing
performances on an industrial geometry
Development of filtered Euler–Euler two-phase model for circulating fluidised bed: High resolution simulation, formulation and a priori analyses
Euler–Euler two-phase model simulations are usually performed with mesh sizes larger than the smallscale structure size of gas–solid flows in industrial fluidised beds because of computational resource limitation. Thus, these simulations do not fully account for the particle segregation effect at the small scale and this causes poor prediction of bed hydrodynamics. An appropriate modelling approach accounting for the influence of unresolved structures needs to be proposed for practical simulations. For this purpose, computational grids are refined to a cell size of a few particle diameters to obtain mesh-independent results requiring up to 17 million cells in a 3D periodic circulating fluidised bed. These mesh-independent results are filtered by volume averaging and used to perform a priori analyses on the filtered phase balance equations. Results show that filtered momentum equations can be used for practical simulations but must take account of a drift velocity due to the sub-grid correlation between the local fluid velocity and the local particle volume fraction, and particle sub-grid stresses due to the filtering of the non-linear convection term. This paper proposes models for sub-grid drift velocity and particle sub-grid stresses and assesses these models by a priori tests
Connecting dispersion models and wall temperature prediction for laminar and turbulent flows in channels
In a former paper, Drouin et al. (2010) proposed a model for dispersion phenomena in heated channels that works for both laminar and turbulent regimes. This model, derived according to the double averaging procedure, leads to satisfactory predictions of mean temperature. In order to derive dispersion coefficients, the so called ‘‘closure problem’’ was solved, which gave us access to the temperature deviation at sub filter scale. We now propose to capitalize on this useful information in order to connect dispersion modeling to wall temperature prediction. As a first step, we use the temperature deviation modeling in order to connect wall to mean temperatures within the asymptotic limit of well established pipe flows. Since temperature in wall vicinity is mostly controlled by boundary conditions, it might evolve according to different time and length scales than averaged temperature. Hence, this asymptotic limit provides poor prediction of wall temperature when flow conditions encounter fast transients and stiff heat flux gradients. To overcome this limitation we derive a transport equation for temperature deviation. The resulting two-temperature model is then compared with fine scale simulations used as reference results. Wall temperature predictions are found to be in good agreement for various Prandtl and Reynolds numbers, from laminar to fully turbulent regimes and improvement with respect to classical models is noticeable
Shear-induced self-diffusion of inertial particles in a viscous fluid
We propose a theoretical prediction of the self-diffusion tensor of inertial particles embedded in a viscous fluid. The derivation of the model is based on the kinetic theory for granular media including the effects of finite particle inertia and drag. The self-diffusion coefficients are expressed in terms of the components of the kinetic stress tensor in a general formulation. The model is valid from dilute to dense suspensions and its accuracy is verified in a pure shear flow. The theoretical prediction is compared to simulations of discrete particle trajectories assuming Stokes drag and binary collisions. We show that the prediction of the self-diffusion tensor is accurate provided that the kinetic stress components are correctly predicted
A posteriori study of filtered Euler-Euler two-phase model using a high resolution simulation of a 3D periodic circulating fluidized bed
Gas-particle flows in vertical risers are involved in many industrial scale fluidized bed applications such as catalytic cracking, fossil or biomass combustion. Risers flows are often simulated by two-fluid model equations coupled with closures developed in the frame the kinetic theory of granular media. However, two-fluid model discretized over coarse mesh with respect to particle clustering size are performed for large units because of limited computational resources. Now, it is well established that meso-scales cancelled out by coarse mesh simulations have dramatic effect on overall behaviour of flows. This study proposed a sub-grid modeling approach for effective drag force and particle stresses which accounts for the effects of unresolved structures on the resolved flows
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