CFD Modeling

CFD Modeling Software in:Flux is an advanced Computational Fluid Dynamics (CFD) software that simulates ventilation and dispersion in complex geometries by solving the 3D Reynolds-Averaged Navier Stokes (RANS) equations. It includes a level of automation that is virtually unheard of in traditional CFD software – all domain sizing, meshing, numerical setup and solution monitoring is handled automatically, meaning that the software can be used by the CFD experts and non-experts alike. With just a few clicks, hundreds of CFD simulations can be scheduled to run. Thanks to the compact mesh adaption, simulations usually complete in just a few minutes even for highly complex geometries.

Ventilation and Dispersion

Running ventilation and dispersion simulations in in:Flux is easy. Once a CAD file has been imported, the user simply selects the wind direction and speed, and the software handles the rest. In this way, multiple ventilation cases can be set up in seconds, and the scheduler runs the first simulations immediately.

While the ventilation simulations are running, “inflows” can be defined representing high pressure gas leaks, controlled blowdown events or exhaust emissions. The locations of the inflows are set by clicking on the CAD file. The properties of the inflow, such as velocity, temperature and composition, can either be specified directly, or using the in-build isentropic expansion calculator for high pressure leaks. Setting up dispersion simulations is a simple operation: just select the inflows and select the ventilation, and in:Flux will automatically set up the dispersion cases. This process can occur while the ventilation simulations are running, and the new dispersion simulations will automatically start once the ventilation has complete.

When the simulations are converged, the results can be visualized using contours, streamlines, vectors and isosurfaces. Images can be output directly or to the clipboard, enabling simple reporting. Further processing is available using monitor points and regions, and the results are exportable to Excel.

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Automatic Meshing and Domain Sizing

Automatic Meshing and Domain Sizing Creating a mesh for CFD simulations is normally a laborious process and can take hours with traditional CFD software, but with in:Flux it is done automatically in seconds. To size the domain that contains the mesh, the CAD geometry is analyzed to determine the size of obstructing features in the direction of the wind. Based on this analysis, the domain is expanded around the geometry such that the sides of the domain are positioned optimally. The mesh is then established by successive refinements around the CAD, including boundary layer grading close to the bottom wall. None of this requires any user interaction or setup.

When the simulation is running, in:Flux analyzes the regions of high gradients and automatically refines the mesh so that the accuracy is improved. Conversely, where the mesh contains too much refinement relatively to the gradients, it will the mesh will coarsen. This redistribution of mesh density ensures that the solver converges on accurate solutions with appropriately refined grids.

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Automatic Numerical Setup

Automatic Numerical Setup The appropriate numerical setup for CFD modeling of ventilation and dispersion have been well established, and are automated in in:Flux to ensure the highest quality solutions. The boundary conditions are set such that the upstream face uses a logarithmic expression for the Atmospheric Boundary Layer (ABL), while the remaining boundaries are zero-pressure openings except for the bottom boundary which is a wall. CAD geometry is accounted for using the Immersed Boundary Method (IBM).

All terms of the governing equations are discretized using at least second-order accuracy, with the UMIST TVD scheme providing second-order accuracy for the convection term. Closure of the RANS equations is provided using the SST Turbulence Model. Buoyancy forces are included in the momentum equations, and turbulence production from buoyancy is included in the k-equation.

All of this setup is performed in the background by default and does not require any interaction or choices from the user. This makes in:Flux accessible to the non CFD expert, as high quality numerical setup is the normal mode of operation.

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Multi-Component Releases and Fluids Database

Simulated gas leaks can be setup as pure or multi-components gases. There is no limit to the number of components can be specified. Properties of the multi-component gas, such as the LFL, UFL and Stoichiometric concentrations, are automatically calculated. In addition, multiple gas mixtures can be specified in a single simulation, which may be useful for modeling controlled blowdown events. The DIPPR fluids database provides a comprehensive set of gases to choose from – the user can also create their own gases if needed.

Simulation Scheduler

Simulation Scheduler in:Flux automatically handles the scheduling of simulations, allowing the user to set up hundreds of CFD simulations without the need for writing complex scripts or batch files. By default, simulations are queued such that one will start when the previous one completes. The user can prioritize simulations if results are required early.  The scheduler can be started or stopped at any time.

Post-processing

Post Processing A wide range of visualizations are included with in:Flux, including contours, vectors, streamlines and isovolumes. These provide immediate insight into flow in the domain, whether for ventilation or dispersion. Many variables are available automatically for ease of use. For example, mean age-of-air contours and isosurfaces show regions of poor ventilation for worst-case gas leaks. For dispersion, gas concentrations can be shown either by percent volume, or by percent LFL or UFL.

Monitor Points and Regions

Monitor Points and Regions Monitor points and regions can be added to the in:Flux project at any time. By opening the monitor point analysis window, users have easy access to any variable for all the monitor points. This feature is extremely useful for gas detection, or scenarios based gas mapping studies, as the monitor points can show the gas concentration for each dispersion simulation. Monitor regions provide information about gas volume and mass, and can be used for sizing gas clouds for explosion studies or geographic gas mapping. All data collected in the monitor points and regions can be exported to Excel for further processing.

CAD Integration

CAD Integration in:Flux uses the same powerful CAD importer as Detect3D, supporting the integration of Microstation® (DGN), Autodesk AutoCAD® (DWG, DXF), STEP, IGES, OBJ and STL files. The DGN file format is available as an export option from PDMS software and SmartPlant. CAD objects can be edited and created in the software, either using the 3D interface, or built up from 2D CAD files and images. The import of very complex CAD files is fast even for full models of onshore or offshore facilities. 

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