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

3D numerical simulation of Circulating Fluidized Bed: comparison between theoretical results and experimental measurements of hydrodynamic

This work was realized in the frame of the European GAYA project supported by ADEME. This paper presents a description of the hydrodynamic into a CFB according to experimental measurements of gas pressure and solid mass flux. These experimental data are compared to three dimensional numerical simulation with an Eulerian approach. The obtained numerical results show that the applied mathematical models are able to predict the complex gas-solid behavior in the CFB and highlight the large influence of the particle wall boundary condition. Indeed, it is shown that free slip wall boundary condition gives a good prediction a solid mass flux profile in comparison with experimental measurements nevertheless a convex shape. Moreover, the numerical solid hold-up is underestimated compared to the experimental data. On the contrary, a no-slip boundary condition improves the profile shape of solid mass flux but highly overestimates its intensity and the solid hold-up. A compromise appears to be a friction particle-wall boundary condition such as Johnson and Jackson (1) but the model parameters have to be chosen very carefully especially the restitution coefficient

Numerical study of solid particle axial mixing in a fixed cylindrical drum with rotating paddles

Axial mixture characterization is a wide spread problem in granular particle blending processes such as in an horizontal drum mixer. The homogeneous mixture of particles is obtained by blending the particles via rotating paddles in a fixed cylindrical drum. This problem, common to many technological devices, is crucial in the manufacture of a broad variety of industrial products, such as polypropylene. The granular flow behavior in these systems is still poorly understood and the numerical study of such configurations receives increasing academic and industrial attention. In this paper, a study is conducted to investigate the effects of different aspects of the reactor design on the axial transport of monodisperse, uniform density and spherical polypropylene particles. Results show that principally the shape of the paddles is the important design consideration to enhance the axial transport of particles

Numerical simulation of a 3D unsteady two-phase flow in the filling cavity in oxygen of a cryogenic rocket-engine

The feeding of the LOX dome of a cryogenic rocket-engine is a decisive stage of the transient engine ignition. However flight conditions are difficult to reproduce by experimental ground tests. The work reported here is part of an ongoing research effort to develop a robust method for prediction and understanding the LOX dome feeding. In the framework of this project, experiments with substition fluids (air and water) are conducted, without mass and energy transfer. This work presented here intends to reproduce these experiments through incompressible two-phase flow CFD simulations, in an industrial geometry equivalent to the experimental mock-up, made up of a feeding piper, a dome and 122 injectors. More precisely, the aim is to compare the numerical results obtained with NEPTUNE CFD code with the experimental results, through the dome pressure and the mass flow rate of water at the outlet. An important work was made to obtain the same inlet conditions in NEPTUNE CFD code as the experimenters, in order to compare the numerical results with the experimental results for the best. The influence of the interfacial momentum transfer modeling and turbulence modeling are also studied here. The turbulence modeling plays no macroscopic or local role on the mass flow rate of water, on the mass of water in dome and on the dome pressure. The drag model has a major impact on our results as well globally as locally, unlike the turbulence modeling. The Simmer-like model is prefered in comparison to the Large Interface called LIM, because it is in better agreement with experimental data. Moreover, it has to be highlighted that the Simmer-like model is very sensitive to its parameter d, the inclusion diameter

HPC large scale simulation of an industrial fluidized bed and applications to chemical engineering processes with NEPTUNE_CFD

Fluidized beds and more broadly dilute and dense particle-laden reactive flows are encountered in a wide range of industrial chemical engineering applications such as catalytic polymerization, coal combustion … Nowadays, it is possible to perform realistic 3D simulations of industrial configurations using an unsteady Eulerian multi-fluid approach for polydisperse reactive flows with a good physical modelling. Hence CFD is a powerful tool for studying the optimization of chemical processes, new designs and scaling-up. To obtain numerical results in an acceptable CPU time, it is important to check the feasibility of CFD simulation of fluidized bed flows in complex geometries at industrial scale. Also we need to estimate HPC capacities of CFD tools. Numerical simulations have been performed with the solver NEPTUNE_CFD: parallelized unstructured code (MPI) using unsteady Eulerian multi-fluid approach. NEPTUNE_CFD is based on the same numerical methods than Code_Saturne. Code_Saturne is an open source CFD software code ready to run on petascale machines. NEPTUNE_CFD’s high parallel computing performances for particle-laden flows have been demonstrated over last years. Recent developments allow overtaking NEPTUNE_CFD’s limitations making it fit for massive parallel computing. Please click Additional Files below to see the full abstract

High performance computing (HPC) for the fluidization of particle-laden reactive flows

The present paper shows the parallel computing performance (up to 4,096 cores) of a numerical solver for simulation of dense reactive multiphase reactive flow such as fluidized bed reactor. NEPTUNE_CFD V1.08 is a parallelized unstructured code solving unsteady Eulerian multi-fluid approach. The meshes have up to 38,000,000 cells. The simulations show an excellent scalability up to 2,536 cores

Numerical simulation of unsteady dense granular flows with rotating geometries.

In chemical engineering applications, it is not uncommon to encounter reactors featuring rotating parts. As these rotating parts are present in order to enhance processes such as chemical reactions and/or ensure homogeneity, it is essential to take them into account to perform predictive numerical simulations. This aspect can be particularly challenging, even more so when complex industrial geometries are to be treated.In this paper a numerical methodology for simulating unsteady granular flow in rotating geometries is presented. The method is based on splitting the domain into static and rotating parts. The information between rotating and static parts is passed by a non-conformal mesh matching technique. The presented methodology is validated numerically by comparing its results with other conventional methods. The method is then applied to an industrial scale problem. The applicability of the method and the way it may be used to investigate complex flow is demonstrated. Therefore this approach enables to consider the full geometry of complex reactors. It opens the door to further investigation, optimization and design of industrial scale chemical processes

Computational study of dense granular flows in stirred reactors

In chemical engineering applications, reactors featuring rotating parts are common practice. As these rotating parts are present in order to enhance chemical reactions, it is essential to take them into account when performing predictive numerical simulations. This aspect can be particularly challenging, even more so when complex industrial geometries are to be treated. In this communication the rotating mesh numerical methodology of NEPTUNE_CFD V3.0 (an Eulerian n-fluid multiphase flow CFD code) is presented. The method is based on splitting the domain into static and rotating parts. The information between rotating and static parts is passed thanks to a non-conformal mesh matching technique. The methodology is first validated, both numerically and experimentally using the classical rotating drum case. The high degree of compaction of the flow is taken into account thanks to a frictional stress tensor. The method is then pushed further and used to investigate the hydrodynamics of dry granular beds in stirred vessels. The results show that the rotating mesh method can effectively treat such configurations, hence offering interesting insight concerning the dynamics of the flow

Numerical simulation of dome filling in an experimental rocket engine mockup

Experiments are carried out with substitution fluids (air and water), without heat and mass transfer on a rocket engine mockup. The work presented here intends to reproduce the experimental results using incompressible twophase flow simulations. The geometry used is representative of the experimental mockupcomposed of a feeding pipe, a dome, and a number of injectors. The objective of the paper is to adapt a Eulerian–Eulerian two-fluid model approach to simulate the filling of a dome and to test its ability to reproduce some experimental evidences. The main difficulties to be faced are the fast transients in a complex geometry, including in particular the valve opening sequence, and the drastic evolution of the two-phase flow regime as the flow evolves from gas only to liquid only. An important work has been conducted to obtain the proper inlet conditions to be imposed in the code in coherence with the experiments. The influences of the turbulence modeling and the interfacial momentum transfer modeling are also studied. The former has no macroscopic or local effect on the mass flow rate of water, the mass of water in the dome, and the dome pressure. The drag model, however, has a major impact on the results as much globally as locally. The Simmer-like drag model is preferred in comparison to the Large Interface Model, due to a better agreement with the experimental data. Moreover, it has to be highlighted that the Simmer-like model is very sensitive to the inclusion diameter

The emptying of a bottle as a test case for assessing interfacial momentum exchange models for Euler–Euler simulations of multi-scale gas-liquid flows

Simulating gas-liquid flows involving a wide range of spatial and temporal scales and multiple topological changes remains a major challenge nowadays, as the computational cost associated with direct numeri- cal simulation still makes this approach unaffordable. A common alternative is the two-fluid Euler–Euler formulation that avoids solving all scales at the price of semi-empirical closures of mass, momentum and energy exchanges between the two fluids. Many of such closures are available but their performances in complex flows are still in debate. Closures considering separately large gas structures and smaller bub- bles and making these two populations evolve and possibly exchange mass according to their interac- tions with the surrounding liquid have recently been proposed. In order to assess the validity of some of these closures, we carry out an original experiment in a simple configuration exhibiting a rich succes- sion of hydrodynamic events, namely the emptying of a water bottle. We simulate this experiment with the NEPTUNE_CFD code, using three different closure approaches aimed at modelling interfacial momen- tum exchanges with various degrees of complexity. Based on experimental results, we perform a detailed analysis of global and local flow characteristics predicted by each approach to unveil its potentialities and shortcomings. Although all of them are found to predict correctly the overall features of the emp- tying process, striking differences are observed regarding the distribution of the dispersed phase and its consequences in terms of liquid entrainment