|October 2, 2001, 16:49||
Re: CFX 5.5
This upcoming release of CFX-5 has a lot to offer. What follows is rather long, but you asked...
CFX-5.5 is a major upgrade to CFX-5, bringing a range of new physical models and new tools to the CFX-5 system. As usual, all capabilities are available using the coupled multigrid and scalable parallelisation provided for CFX-5's solver technology.
<h3>Generalised Grid Interface (GGI)</h3>
The Generalised Grid Interface (GGI) capability significantly enhances the geometric flexibility of CFX-5, and allows a 'divide-and-conquer' approach for complex problems. With this capability a user can independently generate a set of meshes for different sections of a problem, using any tools or mesh structure within each component. The individual grids are then read into CFX-Build, positioned and scaled (if necessary), and combined into a single analysis using GGI to interface the mismatched grids.
Periodic GGI connections are also supported, allowing periodic flow between two sides of a domain with mismatched grids.
<h3>Multiple Frames of Reference</h3>
Multiple Frames of Reference (MFR) allows the analysis of situations involving domains that are rotating relative to one another. For CFX-5.5, this feature focuses on the investigation of rotor/stator interaction for rotating machinery using the Frozen Rotor frame change model. Since MFR is based on the GGI technology, the most appropriate meshing style may be used for each component in the analysis.
<h3>Combustion & Radiation</h3>
This release introduces gaseous combustion modelling capabilities to CFX-5. Single or multi-step reactions are solved using the Eddy Dissipation Model (EDM), with or without chemical kinetics. For multistep reactions, <ib>CFX-5's coupled solver technology is used to simultaneously solve all components and accelerate convergence when there is complex reaction mechanics</ib>. The modelling of flame ignition and extinction is also included through chemical timescale, temperature and mixing rate limiters.
Significant advances have been made in extending the range of applicability of the coupled multiphase modelling capability first introduced in CFX-5.4.1. The available interactions with other models in the solver have been significantly extended, and new modelling capabilities have been added.
<h4>Additional Variables & Multicomponent Fluids</h4>
Additional Variables and Multicomponent Fluids can now be used in a multiphase analysis. The additional variables can be transported and exchanged between fluids, and either phase may be defined with variable composition and density.
<h4>RFR & Periodicity</h4>
Single frame Rotating Frame of Reference is now supported for multiphase calculations, and node-to-node periodicity can be used in rotating or stationary cases.
An energy equation is now available in each phase (missing in CFX-5.4.1), and energy can be transferred between phases.
<h4>Momentum & Energy Sources</h4>
Users can define their own sources or sinks of momentum or energy in either phase in a multiphase analysis. The sources can have constant value, or be defined through the CFX Expression Language for a high degree of flexibility and user modelling capability.
<h4>Dense Particle Effects and Solid Pressure Forces</h4>
Models for dense particle effects within an Eulerian multiphase calculation are provided in CFX-5.5. The models include Wen Yu and Gidaspow drag models, as well as Solid Pressure Forces to limit packing density.
<h4>Turbulence Dispersion Forces</h4>
Dispersion forces due to turbulence in a particle phase can now be modelled in CFX-5.5
CFX-5.5 includes free surface modelling as a 'Visible Beta' feature.
The free surface implementation in CFX-5 is a homogeneous extension to Euler multiphase and solves a single set of momentum and volume fraction equations for free surface flows. CFX-5 uses a unique 'compressive' discretisation scheme to ensure sharp interface capture within 2-3 elements. Compressive transients are also used for unsteady cases.
Sources (or sinks) of Mass can now be defined within a sub-domain for single-phase calculations. Mass sources can be specified with incoming velocity, temperature, scalar concentration, etc.
To this point, sources in CFX-5 have been defined solely in volumetric sub-domains within the problem. With CFX-5.5, advanced users can use CCL to specify sources or sinks for any equation at a point in space.
CFX-5.5 includes the latest in two equation turbulence models and wall treatments. The SST and K-Omega turbulence models are now available within CFX-5. Turbulent wall treatments have been advanced to use the 'scaleable' wall function or low-Re integration to the wall. An 'automatic' near wall treatment option is also provided to allow the solver to locally pick the best option depending on local flow regime and near-wall mesh. The 'scaleable' wall function (now the default in CFX-5.5) is an extension to the traditional log-law and provides improved results and robustness over a broader range of near-wall grid spacing.
A number of other turbulence improvements have also been made. The "second moment closure" or "Reynolds Stress" model has been re-implemented and improved significantly in terms of robustness and accuracy. Boundary conditions for all turbulence models have been extended to include "viscosity ratio" specification. Finally, a Large Eddy Simulation (LES) model is available in the CFX-5.5 solver as a Beta capability.
CFX-5.5 includes a number of features to make the meshing of real-world geometries more automated and easier than ever.
<h4>Multiple Surface Meshing</h4>
Multiple surface meshing allows the user to group multiple surfaces together for the purposes of meshing, thereby significantly decreasing the sensitivity to the details of the CAD geometry. The user can define a group of surfaces, which is then automatically re-parameterised and can be meshed, ignoring any internal surface boundaries.
<h4>Small Edge Elimination</h4>
Very small CAD edges (usually artefacts from CAD import) can be automatically eliminated by specifying an edge tolerance. This prevents excessive refinement around these small edges and results in a high quality and more appropriately spaced mesh.
<h4>Sliver Surface Elimination</h4>
Some CAD geometry's contain very small sliver surfaces that cannot be meshed or re-parameterised in a multiple surface group. CFX-5.5 provides a sliver surface elimination tool that allows the user to specify surfaces to be meshed over by the surface mesher, addressing these problems without modification to the underlying CAD.
Automatic curvature sensitivity and edge proximity detection have long been useful tools for generating meshes in complex geometries with a minimal amount of user interaction. CFX-5.5 takes this one step further with the introduction of 3D proximity detection. This feature automatically refines the mesh in areas where geometric features come together and result in small spaces within the volume.
<h4>CAD Quality Check</h4>
The best place to find potential CAD problems is before they ever reach the mesher. CFX-5.5 provides a CAD quality check tool to identify sliver surfaces, poorly parameterised surfaces and other CAD problems that may cause difficulty in the mesher. The user can then fix the CAD or use some of the above tools to allow meshing to proceed as smoothly as possible.
<h3>CFX Expression Language Functions</h3>
The CFX Expression Language (CEL) has been extended with two new intrinsic functions that allow the value of an expression to be set via 1D or general profile data. In the Expression Editor you can now create '1D Interpolation' or 'Cloud Interpolation' functions, and then use these in any subsequent expression. The interpolation data can be entered manually, or imported from an external file.
<h4>Extended Data Evaluation</h4>
A large number of new features and functions have been added to CEL to allow the evaluation of flows, averages and geometric quantities from within expressions. For example, surface area, mass flow or variable averages can be evaluated over any boundary locator. With this capability it is now possible to (for example) compute an average of a variable on one boundary and use it in the expression for another boundary.
The MPI (Message Passing Interface) library is now available as an option for the parallel communication library within the CFX-5 Solver. MPI has been shown to improve parallel efficiency when running local or homogeneous distributed parallel on some systems.
Parallel partitioning algorithms have been improved. Advanced control of the Metis algorithm allows partitioning with user defined weighting factors, and the recursive bisection algorithm no longer limited to the number of partitions being a power of 2.
The transient evolution of flow quantities at a point in space can be monitored by creating 'Monitor Points' in a CFX-5 solver run. These are considered to be a Beta feature, as an interface for specifying monitor points does not exist in CFX-Build. Monitor points are defined by manually adding them to the CCL definition of the solver run.
CFX-5.5 allows users to create their own source code subroutines and link them into the CFX-5 solver for the creation of custom models, properties, boundary conditions, etc. In CFX-5.5 anything that can be set by an expression may use a user subroutine to define the value. A range of utility functions to access solver data is supplied and can be used in creating the user subroutines. In essence, users can create there own "built-in" functions for use in CEL expressions. A generic "junction box" routine can also be used to perform custom functions / control at various points in the solver.
Some numerics defaults have been changed for transient analyses to accelerate convergence within a timestep. Time accurate solutions can be obtained by running 3 inner iterations within a timestep.
<h4>Smart Start & Auto-timestepping</h4>
The default behaviour of Smart Start and Auto Timestep have been modified. Smart Start is the temporary modification of physical models and solver parameters to improve early convergence behaviour, and Auto Timestep allows the solver to derive a reasonable (but conservative) Physical Timestep during solution. In CFX-5.4.1 these were coupled (Smart Start was automatically chosen when Auto Timestep was enabled), and could not be controlled in any other manner. In CFX-5.5 these have been separated and the user has separate control of the timestep and smart start strategy. The internal algorithms for each have also been improved.
CFX-Build now provides a widget to request the regular backup RES file as the solution proceeds. These backup files are written to the temporary run directory and are available in the event of a catastrophic solver or system failure.
<h4>Double Precision and Optimised Solvers</h4>
Double precision versions of the CFX-5 solver executable are now provided for some system architectures. In addition to the existing optimised solvers for the HP PA2 architecture, an optimised solver for Pentium III/IV processors running Linux provides an additional 20-30% performance improvement.
The CGNS (CFD General Notational System) format is now supported for grid import and results export.
<h4>DEF File Editor</h4>
The handling of expert parameters is significantly improved, and a list of the most commonly used parameters and their values is accessible directly from within the editor.
As with all releases, CFX-5.5 provides the latest version of Patran as the basis for the meshing and physics pre-processor CFX-Build. In this release, CFX-Build is based on Patran 2000 (a.k.a. Patran 9.5), and provides updated CAD interface tools as well as the following benefits.
<h4>Windows NT/2000 Implementation</h4>
For the first time, Patran 2000 provides a native Windows NT/2000 implementation of CFX-Build. This means the look and feel of CFX-Build has changed significantly on Windows platforms to be more consistent and comfortable to Windows users. The look and feel on Unix platforms remains unchanged. <bi>As of CFX-5.5, the Exceed product from Hummingbird is no longer required to run CFX-Build, and is not supplied as part of the CFX-5 product.</bi>
To facilitate the generation of meshes for MFR and GGI analyses, CFX-Build can be run in meshing-only mode. This allows the generation of meshes and labelled regions on created or imported geometries, without the specification of any physics information. The result is a DEF file containing just mesh information for import into a subsequent CFX-Build session.
<h4>Patran Native Meshing</h4>
Meshing-only mode also provides advanced users with access to all of the native surface and volume meshing tools available in native Patran. This allows the creation of hexahedral meshes, extruded meshes and other mesh types not available with CFX-5's unstructured mesher. Some advanced knowledge of CFX-Build is required as regions are defined as node/elements groups, and import/export is done via the Patran neutral formal.
The relationship between domains and subdomains can be a tricky issue when dealing with many domains of complex topology. CFX-Build now provides a Domain/Verify feature that can be run after domain and sub-domain creation, to graphically examine the resulting domain topology and boundary surfaces.
CFX-5.5 is the introduction of CFX-Post as the primary post-processing tool for CFX-5 simulations. As the successor to CFX-Visualise, CFX-Post uses modern user interface paradigms that will be immediately familiar to many users. The user interface is highly configurable and can be easily switched between Windows and Motif styles. As well as the standard interactive mode, CFX-Post will also easily execute post-processing session files in batch mode to quickly reproduce output for a series of runs.
CFX-Post aims to provide our users with all the graphical features they have come to expect. Isosurfaces, planes, vectors, surface plots and streamlines will be available to display the flows within the user's domain. Flexible region creation includes the ability to generate Boundary/Plane intersection curves and to limit the extents of slice planes using circular or rectangular bounds. The latest in key-frame animation capabilities are also available.
As well as the 'usual' visualisation features, a key objective of CFX-Post is to provide flexible and accurate quantitative post-processing of CFX-5 results. CFX-Post enables the full power of the CFX Expression Language within the post-processor, and extends it with a range of post-processing specific functions such as exact mass flow, area, length and volume integrals and averages of any quantity. Expressions can also be used to define new variables for the presentation of user specified quantities. Advanced users can also use 'Power Syntax' within CFX-Post session and state files. Power Syntax provides access to a complete programming language (the Perl scripting language), to allow the creation of subroutines, loops, logic and file I/O for maximum customisability and automation of quantitative and graphical post-processing.
Post is also extended to the control of the CFX-5 Solver, with the introduction of a new solver manager for CFX-5.5. This new solver manager offers simplified run definition and control, user configurable graphs, and ability to monitor multiple runs simultaneously. With the new solver manager, not only residuals, but also boundary flows, forces, balances and user-defined monitor points can be dynamically displayed and monitored as the run proceeds.
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