Background and Purpose
The turbulent fluid dynamic COM3D code was developed at the Institute for Thermal Energy Technology and Safety (ITES), in the Karlsruhe Institute of Technology (KIT) with the aim to simulate combustion including explosion and detonation, transport and mixing of hydrogen and other gases in nuclear reactor containments and other industrial facilities.
The turbulent reactive flow code is intended to model development of large-scale combustion events in geometrically complex environment with multiple compartments and internal structures in a multi-block computational domain.
Results
The COM3D code simulations provide the complete 3D fluid dynamic information of gas species and discrete particle distribution, including their velocities, densities, parameters of the flow turbulence, etc, and pressure and temperature loading on the walls and internal structures participating in an event.
Application
COM3D has been used in the simulations of the combustions and explosions, together with the system of industrial risk mitigation of hydrogen and burnable gases in nuclear containment and auxiliary buildings and in complex nonnuclear facilities.
It has been applied for parametric study of the influence of geometrical design and of the accident scenario details on the potential risk resulting from pressure and thermal loads in the conditions of severe accident. The code was used to study combustion of the gaseous systems in wide range of the initial and boundary conditions for different combustion regimes ranging from slow deflagration to strong flame acceleration and detonation.
Physical Models
COM3D is a finite-differences code based on well established numerical practice solving the compressible Navier-Stokes equations in three- dimensional Cartesian space. The code utilizes a set of transport equations for every gas species and for total energy, mass and momentum. The code takes into account the influence of the gravitation.
The COM3D code for the modeling of the flow turbulence can use either Reynolds Averaged Navier-Stokes (RANS) or Large Eddy Simulation (LES) method. Three turbulence models are available in COM3D in the frames of RANS approach:
• standard κ−ε model;
• renormalization group (RNG) κ−ε model;
• shear stress transport (SST) model;
and three sub-grid for LES method:
• eddy viscosity – eddy diffusivity method;
• mixed eddy viscosity – eddy diffusivity method;
• dynamic eddy viscosity – eddy diffusivity method.
Wall shear stresses are provided for both laminar and turbulent flow though wall functions.
The code includes well developed infrastructure for the combustion simulation. The combustion ignition starts with the ignition procedure which allows the control the intensity and the duration of the ignition, allowing, e.g., to mimic the spark and glow-plug- type of igniters.
A set of combustion models is available in the code; it incorporates both classic models and the newest developments, providing necessary flexibility and robustness in the calculations. The following models are at the moment offered for the combustion:
• integral combustion model KYLCOM;
• set of effective reaction rate models, as EBU, EBU-SB, Hjertager, Eddy-diffusivity, and other models;
• reduced and detailed kinetic mechanisms
• and detonation and DDT mechanisms.
For detonation simulation few models can be applied, e.g., one-step Arrhenius reaction and Heaviside-function model.
The particle model allows to reproduce discrete particle behavior, e.g., allowing the code to simulate missile movement history.
Thermodynamic properties of the gases are based on the linear approximation of the JANAF tables for the thermodynamic properties of the real gases, and one of several available equations of state.
Numerical Schemes
The mesh used in COM3D code is rectangular Cartesian equidistant uniform multi-block simply connected domain with cell-centered variables. The transport of the basic variables is provided using one of several available numerical algorithms:1st order upwind, 2nd order total variation diminishing (TVD), 2nd order van Leer, HLL, HLLC, AUSM, AUSM+ up.
The time integration accuracy depending on the selected method is either of the 2nd order or of the 4th order (Runge-Kutta method).
Platforms, Pre- and Postprocessing
The COM3D code is available for all UNIX based computers carrying one of the common implementation of MPI (OpenMPI). The code is written largely using C++ program language with some parts using FORTRAN and Python languages..
For the data input either a textual input or simplified GUI can be used, while for the Post-processing the commonly available tools as VisIt, Paraview, and others, can be used due to standardized data storage format.Documentation
The COM3D code is distributed with comprehensive User and Tutorial Guides. The current release includes documentation for version 5.0 not fully updated and partially for version 4.10.