Grids, Numerics & Parallel Processing
Several enhancements to the numerics in FLUENT 6.2 result in improved solver accuracy and efficiency. For the segregated solver, an improved Rhie-Chow interpolation technique has been implemented that can significantly improve accuracy on tetrahedral meshes. In addition, a new locally 3rd order discretization scheme has been implemented for both the segregated and coupled solvers.
FLUENT 6.2 provides significant improvements for transient simulations with the implementation of non-iterative transient solution methods. A non-iterative PISO solution scheme is available as well as an implicit fractional step method. Both methods are applicable for incompressible and mildly compressible flows and result in significant speed-ups compared with the iterative transient solution method.
Improvements have been made to the coupled solver that result in better accuracy along with a speed-up in the time required per iteration. Additional modifications were made for unsteady cases that result in improved accuracy and convergence for the coupled solver when implicit time-stepping is used. In particular, the coupled implicit solver now captures pressure wave propagation with accuracy similar to the coupled explicit solver. Further, the number of iterations required for these problems is significantly reduced.
Of particular interest to turbomachinery users is automated full multigrid initialization. This feature allows an initial solution field to be computed so that a higher Courant number can be used with the coupled implicit solver, resulting in faster overall convergence. Non-reflecting boundary conditions are now supported for unsteady flows.
FLUENT 6.2 also includes substantial improvements to the speed of reading cases files into the parallel version of FLUENT.
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Liquid free surface predicted using VOF and non-iterative time advancement
Heat Transfer, Phase Change & Radiation
A new solar load model has been implemented in FLUENT 6.2. The solar load model allows the radiant energy transport between the sun and a wall surface to be solved, based on the intensity and position of the sun. This model is important for automotive and building climate control applications.
For the discrete ordinates (DO) model, a second order discretization option is now available for obtaining more accurate results, particularly for cases with high optical thickness. A UDF can be used to customize the absorption coefficient for each band with the gray-banded DO model. Several improvements have also been made to the surface-to-surface radiation model, including the ability to specify the number of faces per surface cluster for different boundaries, allowing fine clustering to be used only where it is needed. The result is a more accurate solution without the memory penalty associated with using fine clustering everywhere.
A wet steam model has been implemented in FLUENT 6.2. Two-phase flow in steam turbine applications is one area that will benefit. Cases with shell conduction no longer require encapsulation in parallel; this significantly improves calculation efficiency. Several enhancements have also been made to both the cavitation and heat exchanger models.
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Solar heat flux in an automobile cabin
Courtesy of National Renewable Energy Laboratory
Dynamic & Moving Mesh
While the dynamic mesh model has served as the foundation for automotive in-cylinder applications, it has been widely used for other industrial applications as well, ranging from chemical process to biomedical. Dynamic hanging node adaption, new in FLUENT 6.2, allows for more accurate solutions with lower overall cell counts. The remeshing and layering capabilities have been expanded, and include the use of symmetry boundary conditions with local re-meshing, and a flexible “2.5-D” remeshing technique that is particularly useful for simulating certain types of pumps. A new built-in six-degrees-of-freedom solver is also available for applications with unconstrained motion, including store separation, missile launch, and tank sloshing. Parallel scalability has also been improved.
A new sliding mesh model is available in FLUENT 6.2 that addresses robustness issues associated with earlier versions of the model. The improvements also apply to non-conformal interfaces in general.
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Prediction of wall shear stress for a lobed pump
Reacting Flow
FLUENT 6.2 includes models for diesel autoignition and gasoline spark ignition. A new stiff chemistry algorithm for the segregated solver is available for laminar flows. When combined with ISAT, laminar finite rate chemistry problems can be solved more quickly and efficiently. Several enhancements have also been added to the NOx model. Surface chemistry mechanisms can be imported in the Surface CHEMKIN format. Another useful new feature is the ability to create custom material databases. This allows material properties and reaction mechanisms that have been specified in one case to be used again in a different case. PrePDF has been completely integrated into FLUENT 6.2. In addition to improved usability, the integration has also resulted in reduced computation times.
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Temperatures on a flame surface
Turbulence & Acoustics
In the area of turbulence modeling, there is an effort underway to improve the large eddy simulation (LES) capability. FLUENT 6.2 includes several new sub-grid scale viscosity models, including two dynamic models that improve the quality of LES predictions. To help accelerate convergence, an LES simulation can be launched from a steady-state RANS solution using turbulence synthesization. Two new methods for specifying the stochastic velocity boundary condition at inlets, more rigorous than previous offerings, are now available. The usability of the detached eddy simulation (DES) model has also been enhanced.
FLUENT 6.2 provides an unparalleled suite of acoustics capabilities. The Ffowcs-Williams Hawkings (FW-H) model that was introduced in FLUENT 6.1 has been extended to handle rotating surfaces, so that fan noise can be modeled. When used in conjunction with rotating reference frames, fan noise predictions can be obtained based on a steady-state simulation, providing an efficient and powerful tool. The FW-H model is now also available with the coupled solver. A new set of broadband source models allows acoustic sources based on the results of steady-state simulations to be estimated. These models are practical tools for evaluating design modifications.
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Acoustic power level on the surface of a sedan
Multiphase
A major new improvement for multiphase systems is the ability to include species transport and homogeneous reactions with all multiphase models, including the Eulerian and VOF models. For heterogeneous reactions, the reaction rates must be specified in a user-defined function (UDF); however, the stoichiometry is easily specified in the graphical user interface (GUI). The Reynolds stress turbulence model can now be used in conjunction with the Eulerian model for the prediction of highly swirling multiphase mixtures. Several enhancements have been added to the granular model to produce more realistic results in certain circumstances. The granular model is now available with the mixture model, providing an economical alternative to the full Eulerian model when appropriate.
Several improvements have been made to the VOF model. A new variable time-stepping scheme provides improved robustness and efficiency for cases where the velocity changes significantly with time, as with tank sloshing and filling. An interface-capture scheme provides more efficient convergence for free surface problems in which the final steady state solution is more important than intermediate solutions, as is common in certain ship hydrodynamics applications. An open channel boundary condition and support for inviscid flows further improves FLUENT’s capabilities for marine applications.
A new wall film model has been added to FLUENT’s suite of spray models. It is particularly important for in-cylinder combustion simulations. New tracking schemes, automated tracking scheme selection, and error-controlled time-step adaption result in more accurate and efficient particle tracking with the discrete phase model.
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Breaking ocean waves on an oil platform
Postprocessing
FLUENT 6.2 has some new tools for post-processing and reporting. Users can view multiple monitor quantities in a single window. The autosave capability for case and data files has been made more flexible and is also available for mesh motion preview calculations.
Several enhancements have been made in the area of particle and pathline postprocessing. Users can export particle and pathline trajectories to a file that can be imported and redisplayed, allowing for different injection conditions to be compared without having to recompute the trajectories. In addition, pathline coordinates can be imported by GAMBIT so that geometry can be generated and used for design refinement.
Animations of particle trajectories and pathline trajectories can be created during both steady and unsteady simulations. New options for particle trajectory display provide improved efficiency. The ability to skip a specified number of particle injection locations during display makes it easier to see trajectories in cases with many injections, and coarsening the plotting of each trajectory allows users to speed up the display of trajectories.
There are also enhancements to FLUENT’s data export capabilities to both Fieldview and Ensight. For Fieldview, this includes support for region and surface-based results as well as the ability to export 2D results. For EnSight, new transient export options have been provided.
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Fine and coarse particle migration through a patient's airway during a breathing cycle
Courtesy of Materialise Ltd
Customized Tools
FLUENT 6.2 includes add-on modules for proton-exchange membrane (PEM) fuel cells and solid oxide fuel cells (SOFC). The modules will be included on the FLUENT 6.2 CD, but a special license will be required to activate them. A new kinetics add-on module from Reaction Design is available for FLUENT 6.2. In addition to handling stiff laminar kinetics, it will also handle turbulence-chemistry interaction. This allows users to use consistent kinetics between CHEMKIN and FLUENT simulations.
FLUENT 6.2 allows you to load and manage multiple UDF libraries instead of having to include all of the functions that you need to use in a single library. New or improved UDF hooks are also available for several features in FLUENT 6.2, including NOx modeling, granular physics, discrete phase modeling, multiphase reactions, radiation modeling and more, in order to continue broadening the wide range of customization possibilities available to users.
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Hydrogen distribution on a solid oxide fuel cell
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