• .msh.h5 (Common Fluids Format)

• .msh (legacy)

• .msh.gz (legacy, compressed version of .msh)

• .cas.h5 (Common Fluids Format)

• .cas (legacy)

• .cas.gz (legacy; compressed version of .cas)

• .dat.h5 (Common Fluids Format)

• .dat (legacy)

• .dat.gz (legacy; compressed)

• .cdat (legacy; variables interpolated to nodes specifically for CFD-Post)

• .cdat.gz (legacy; compressed version of .cdat)

• You need to be careful when choosing geometry names in Fluent when the file will be read in CFD-Post. The geometry names must not contain special characters such as '-', '|', and ':'. All such characters will be replaced by a space (which is allowed in names in CFD-Post).

• There might be problems postprocessing transient Fluent cases that involve changes of geometry name or changes of boundary type at intermediate time steps.

File-based Limitations

• The restrictions on loading CFF files also apply to Fluent CFF Case and Mesh (.h5) files. For details, see Limitations with Ansys CFF Files.

• CFD-Post can read Fluent case files that have imprinted surfaces defined in them. However, the imprinted surfaces are ignored in CFD-Post.

Limited support of files from Previous Versions

• Grid interfaces from Fluent versions 6.3 and older are not supported by CFD-Post. If your .cas file has old grid interfaces, read the .cas and .dat file into Fluent Release 12.0 (or later), run at least one iteration, and save the file to change to the new grid interfaces. This converts grid interfaces to use the virtual polygon method and makes the file readable in CFD-Post. Attempting to read old grid interfaces may cause CFD-Post to exit.

• To postprocess forces or fluxes using the DBNS solver of Fluent for cases from versions prior to Release 12.0, you must read the case into Fluent Release 12.0 (or later), iterate at least once, and then write out the .cas and .dat files.

• Holes may appear in Planes/iso-surfaces created using old Fluent mesh/case files (from earlier than Release 14.5) for hex-core/cut-cell mesh cases.

Limitations When Loading Fluent Files

• There is no support for loading of a subset of domains. All domains are always loaded by CFD-Post.

• CFD-Post cannot read Fluent cases that have CAS and DAT files output in different directories.

• For transient Fluent cases, there is no support for adding or removing time steps in the timestep selector.

Mesh Limitations

• The number of nodes, faces and cells that can be read from files written by Fluent may exceed the number supported by CFD-Post.

• In Ansys Fluent, any cell can have any number of faces. The maximum number of nodes in a polyhedron cell is 256 and in a polygon face is 128 (however the contour-creation algorithm has a limit of 64 nodes per face).

• For some cases (for example, shell conduction model), the number of cells/elements reported by Fluent is more than that of CFD-Post. This difference is due to the additional cells Fluent creates internally for solving some physics; these are never written into the case file. Fluent reports include these cells in addition to those available to CFD-Post.

Limitations With Fluent Cases Defining Rigid Body Motion

• CFD-Post can read zone-motion variables (origin, axis, omega, grid-velocity) on profile boundaries from Fluent files only if the variables are constants. For cases where any of these values are specified as non-constants, CFD-Post ignores the variable. In such conditions, CFD-Post cannot transform the velocity from absolute to the relative frame or the reverse. Other dependent variables (such as Mach Number and Vorticity) will not be available unless explicitly exported from Fluent to a Fluent Postprocessing file or written as an additional variable (see Additional Variables). There will be a warning message issued when these files are read.

Limitations for 2D Cases

• Ansys Fluent can solve 2D problems. The mesh and data within the Ansys Fluent files for these cases is defined using 2D cells and faces.

  CFD-Post will extrude the 2D case on read so that it is displayed as a quasi-3D case.

  If the 2D case is axisymmetric, the extrusion will be performed about the Y-axis such that it forms a 3D wedge.

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  Note:  For axisymmetric cases, the point values in CFD-Post may differ from values reported in Fluent due to the extrusion of the 2D domain in the theta direction.

  ---

  If the case is not axisymmetric, the extrusion will be performed in the direction of the Z axis such that it uses the reference-depth.

• There are very small differences between Fluent and CFD-Post in the way that area is calculated for axisymmetric cases; this area is used in quantitative functions. Fluent calculates the area for any axisymmetric case as , where is centroid-y of the facet. CFD-Post extrudes the 2D geometry to create a 3D wedge (of wedge angle 7.5°) then calculates the area by repeating the wedge to create a 360° cylinder. This is similar to approximating the perimeter of a circle by measuring the perimeter of an inscribed uniform polygon.

• The results of calculations by CFD-Post for Fluent 2D cases are for a reference-depth from the Fluent case file. For axisymmetric cases, the reference-depth is ; that is, the results calculations are for the complete cylindrical region, and not what is shown in the viewer (which is a sector from the complete cylinder). This matches the behavior of Fluent.

  Results will be consistent for all quantitative calculations on all locations. For example, a slice plane will be assumed to be cutting the full cylinder.

Solution Quantities

• Fluent Restart files provide solution data at Cell and/or Face centers. Nodal values are not available. The data provided by Fluent has to be averaged to Node locations for use within CFD-Post.

  Faces in different surfaces that share one or more nodes may provide different face values or their parent cells provide different cell values. Boundaries are therefore given different priorities such that a value from a boundary with a higher priority will be used in the interpolation process over one of a lower priority.

  In a case with two or more domains, in Fluent the nodes on the boundary will get their values from the domain that has the higher priority; CFD-Post uses the average of the boundary values from both domains.

  Fluent Postprocessing files provide results data that may be available at nodal locations. If this is the case, these values will be read from the file and used by CFD-Post. In the absence of nodal data, face and cell data may be available and the use of this data will be governed by the same algorithms (with the same limitations) as those used for Fluent Restart files.

• Only nodal values are used for all qualitative purposes (except for contour plots) and for all quantitative purposes. It is expected that there may be differences in quantitative results when compared to Fluent.

Vector Quantities

• Averaging of vector quantities to nodes differs between CFD-Post and Fluent. In Fluent, vector magnitudes are averaged to nodes explicitly; in CFD-Post, only vector components are averaged to nodes, while the magnitude is calculated from the components at the nodes. The two magnitudes will differ in cases with sharp vector gradients or high face angles (usually due to a coarse mesh).

  For example, if a node has four faces attached that have shear stresses in directions radially away from the node, in CFD-Post the shear stress values at the node will be much smaller in magnitude compared with the face stresses because the stresses in opposite directions cancel out. In Fluent, the direction is ignored and only magnitude is taken into account while calculating the stress magnitude at the node.

• Due to differences between Fluent and CFD-Post in the handling of vector quantities, velocity values can be different on 'interior' zones (conformal domain interfaces).

Domains

• In a case with two domains, the nodes on the boundary in Fluent will get their values from the domain that has the higher priority; CFD-Post uses the average of the boundary values from both domains.

Boundaries

• On boundaries, CFD-Post produces more accurate quantitative results involving geometric variables (such as X, Y, Z) than Fluent reports. This is because Fluent uses geometric variable data from adjacent cell centers instead of the boundary face centers. However, you can get CFD-Post results to match Fluent results exactly by setting the environment variable CFDPOST_MATCH_FLUENT_RESULTS to 1 before running CFD-Post.

• In CFD-Post, on boundaries that have zero velocity, Total Temperature and Total Pressure will have the same values as Temperature and Pressure, respectively (as expected). In Fluent, Total Temperature is different from Temperature for boundaries that have zero velocity; similar differences apply between Total Pressure and Pressure. This is a limitation in Fluent.

  If you export 'Total Pressure' from Fluent, the CFD-Post results will be closer to what Fluent shows.

Periodic Boundaries

• When plotting velocity components on periodic boundaries, there may be differences in CFD-Post, when using Fluent Restart files, compared to Fluent. You should use Fluent Postprocessing files, as outlined in CDAT for CFD-Post and EnSight, to get the correct values.

• A periodic surface in Fluent is actually a pair of surfaces. In CFD-Post this pair appears as a Periodic object and a corresponding Periodic Shadow. When looking at quantitative results in CFD-Post, you need to look at a surface group that contains the "periodic/periodic-shadow" to see output that is in agreement with Fluent's results.

Hanging Nodes

• CFD-Post and Fluent display contours differently in the vicinity of a hanging node. Fluent takes values from cells only on one side, causing a discontinuity of contours. In CFD-Post, the hanging node is made to be a conformal node and takes values from cells on both sides, making a smoother contour.

Interfaces

• For cases with 1:1 interfaces, due to a difference in the handling on nodes at these interfaces, the number of nodes reported by CFD-Post will be different than the number reported by Fluent. However, the number of cells should match.

• Field variables may be discontinuous across an interface that joins domains of differing porosity. Variable values on the interface boundaries are not averaged across the interface. You can inspect variable values on each side of the interface separately.

Specific Variable Considerations when Postprocessing Fluent Results in CFD-Post

• For Fluent results loaded into CFD-Post, all variables, including X, Y, and Z, are stored at either cell centers (for 3D regions) or face centers (for boundary regions) — not at nodes. Fluent can export node based values to Fluent Postprocessing files as outlined in CDAT for CFD-Post and EnSight in the Fluent User's Guide, to get the correct values.

  As a result, when nodal data doesn't exist, the minVal() and maxVal() functions return minimum and maximum cell-centered values of X,Y, or Z on 3D locations, and minimum and maximum face-centered values of X, Y, or Z on boundary regions.

• The nodal based results in CFD-Post are similar but not always identical to those shown in Fluent because Fluent can apply some model-specific transformations not available in CFD-Post when cell and face values are mapped to node values.

• In CFD-Post, a node value on a wall boundary takes precedence over other values for the same node for other boundary types, so all wall nodes will have wall values irrespective of whether they are also used in any other boundary.

• CFD-Post does not smooth out values across non-conformal interface boundaries; that is, there must be a 1-1 mapping of nodes across the interface. As a result, contour and color plots as well as iso-surfaces are discontinuous across these interfaces. Therefore, the node values displayed by CFD-Post at non-conformal interfaces may differ from those shown by Fluent.

• Plots and calculations that are based on node values (rather than cell/face values) can have undesired results where nodes are shared by multiple boundaries at an adjoining edge.

• Also see Quantitative Differences Between CFD-Post and Fluent.

Gradients

• There may be substantial differences between gradients calculated in the Fluent solver and gradients calculated in CFD-Post. The Fluent solver uses options such as boundary treatments and limiters to calculate gradients; CFD-Post calculates gradients independently of the Fluent solver, and does not have access to all of the same data.

  The gradients computed by the Fluent solver can be transferred into CFD-Post by exporting them as variables and then loading them into CFD-Post.

• For Fluent files, the gradients computed by CFD-Post are discontinuous across domains.

Heat Flux

• The variable Boundary Heat Flux Sensible is available only for boundary types velocity-inlet, mass-flow-inlet, pressure-inlet, pressure-outlet, pressure-far-field, and outflow.

• For Fluent files using the energy model, Heat Flux is available for all boundaries and Wall Heat Flux is available only for walls. The values of these two variables will be the same on walls.

  Also see "Wall Heat Flux".

Mass Flow

• CFD-Post may report an incorrect sign for Mass Flow through a conformal internal boundary (known as an "interior" type in Fluent) that is located at the boundary between two domains. To determine the direction of mass flow, use a CEL expression based on the normalized dot product of the local velocity and the face normal. The equations for computing the corrected mass flow through a conformal internal boundary, based on the local mass flow summed over the boundary, are:

  Corrected Mass Flow = sum(abs(Mass Flow)*massFlowCorrectionNorm)@<region>
  massFlowCorrection = Normal X*u + Normal Y*v + Normal Z*w
  massFlowCorrectionNorm = -massFlowCorrection/abs(massFlowCorrection)

• For some cases, the fluxes (Mass Flow()@<surface> or AreaInt(Boundary Heat Flux)@<surface>) from CFD-Post are different from the values reported by the Flux Reports panel from Fluent.

  This is due to some additional physics model-based calculations done by Fluent that are not available in CFD-Post. However, you can use the Fluent Surface Integral or Volume Integral panel results for comparison with CFD-Post.

Mesh Variables

• You cannot use X, Y, or Z variables in expressions or plots in moving mesh transient cases. For example, instead of an Isosurface of X, use a YZ Plane.

Molar Weight

• Molar Weight will always have units of kg/mol in CFD-Post, but units of kg/kmol in Fluent. This will be true for all quantities involving 'mol' or 'kmol' in units.

  To learn how to control the units displayed by CFD-Post, see Setting the Display Units.

Pressure

• In the cavitation model in Fluent, the minimum value for Pressure is limited by the cavitation pressure; this is not done in CFD-Post.

Shear Stress

• CFD-Post will not display any Shear Stress values on coupled non-conformal interfaces as shear stresses are undefined on such interfaces.

• A DBNS solver with laminar flow will have no shear stress on any walls. Force calculations will not include any viscous component in such cases.

Species, Reaction, and VOF

• For Species, Reaction and VOF cases, values in CFD-Post results match with Fluent "Vertex" values instead of "Face" values.

  To have results from CFD-Post match results from Fluent, set the environment variable CFDPOST_BOUNDARY_DATA_FROM_ELEMENTS to 1.

Total Pressure

• CFD-Post reads Total Pressure from the Fluent results file if such data exists. However, if the data is not supplied in the file, Total Pressure is not calculated by CFD-Post.

Unsteady Statistics

• Unsteady statistic variables (such as Mean X Velocity and RMS Static Pressure) are not consistent when read from the standard Fluent Restart file. If needed, you can export these variables explicitly in a Fluent Postprocessing file or append the variables to the Fluent Restart file (see Additional Variables).

User-Defined Memory

• CFD-Post does not support User-Defined Node Memory (UDNM) variables from Fluent.

• CFD-Post reads User-Defined Memory (UDM) and User-Defined Scalars (UDS) as follows:

  • When Fluent Restart files are read into CFD-Post, UDM/UDS variables will appear with names like "User Defined Memory 0"/"Scalar 0".

  • When Fluent Postprocessing files are read into CFD-Post, CFD-Post will show all UDM/UDS variables that were exported to a Fluent Postprocessing file.

• Fluent files do not contain the units for user-defined scalars, user-defined memory, or custom field functions, so these will be dimensionless in CFD-Post.

Velocity

• For Eulerian multiphase cases, the velocity-related variables for secondary phases are incorrect in CFD-Post compared to Fluent when using Fluent Restart files. You should use Fluent Postprocessing files, as outlined in CDAT for CFD-Post and EnSight, to get the correct values.

• Plots of velocity vectors on wall boundaries do not match between CFD-Post and Fluent. Fluent always uses adjacent cell velocity for plotting vectors whereas CFD-Post uses node velocity (interpolated from cell/face values).

• Velocity magnitude values for Fluent in CFD-Post are not in good agreement with Fluent results for cases with multiple-frame-of-reference or sliding-mesh models.

  For cases solved with relative velocity:

  • The Velocity in Stn Frame plotted in CFD-Post is equivalent to Velocity Magnitude in Fluent. Similarly, other quantities dependent on Velocity, such as Total Pressure or Total Temperature, will have the suffix "in Stn Frame" (for example, Total Temperature in Stn Frame, corresponding to Total Temperature) for stationary frame variables in Fluent. Variables in the relative frame of motion will be without this suffix.

  • There is no Fluent equivalent for the CFD-Post variable Velocity because this represents a relative velocity in the local reference frame of the domain (which is not available for postprocessing in Fluent).

  • There is no CFD-Post equivalent for Fluent's Relative Velocity. In Fluent, Relative Velocity is always relative to a global frame of reference (which you can select in Fluent's Reference Values panel; if no reference frame is selected, an absolute velocity is used).

  • When loading Fluent results, CFD-Post does not calculate global ranges by default because this would be too time-consuming (there is a warning to this effect when you load a Fluent case). However, when the variable is used for the first time (for example, when it is plotted), and as timesteps are loaded, the global range will be continually updated.

Volume Fraction

• If Volume Fraction is not available in the list of variables for multiphase Fluent cases, the phase forces reported by CFD-Post will be the same as the total force.

• For the cavitation model, there are differences in the volume fraction values between Fluent and CFD-Post.

Wall Adjacent Temperature

• Nodal values for Wall Adjacent Temperature are only available on faces if they are supplied by Fluent.

  This might result in undefined plots on non-wall locations when using Wall Adjacent Temperature.

  Exporting Wall Adjacent Temperature on non-wall locations from CFD-Post might also show "null" values where data does not exist.

Wall Heat Flux

• The values of Wall Heat Flux reported by CFD-Post for moving and deforming mesh cases will not match those for Fluent. This is because Fluent adds pressure work to get the energy balance.

Wall Heat Transfer Coefficient

• The Global variable range for a Wall Heat Transfer Coefficient is incorrectly reported as zero; use the Local variable range instead.

Processing Fluent Data in CFD-Post

• Plot objects (other than Contour Plots) cannot display cell or face data directly; they can display only nodal averages. However, cell and face data will be used in quantitative reports on volumes, boundaries, planes, iso clips, and isosurfaces (averages, mass flows, integrals). Lines, polyline, and points will use only nodal averages for quantitative calculations.

• Global variable ranges shown in plots are nodal (averaged) ranges.

• CFD-Post does not account for surface tension forces.

• Certain real gas properties are not available for use in CFD-Post: gas constant, molecular viscosity, specific heat, and sound speed.

Case Comparison

• Case comparison is not available for face-based contours of Fluent results.

Contour Plots

• CFD-Post and Fluent might use different sources of data when generating contour plots. For details, see Variable Location: Vertex and Face Options.

• The value ranges shown in a contour plot might differ from the value ranges reported by the function calculator.

• Function calculator results are based on either cell/face values or nodal values, in accordance with how the variables are stored.

Function Calculator

• The Function Calculator might give variable averages on slice planes, isosurfaces, and interiors that are different from those given by Fluent.

  These differences might occur when the surface is cutting through a mesh face that joins two mesh elements. In this situation, CFD-Post might use the element-center data from a different element than Fluent uses.

  Note that as both elements are equally valid choices, both calculations are correct.

• Computing the sum of any variable on any surface returns a value in CFD-Post that is the Fluent value divided by .

Lines

• A line in CFD-Post of type Sample gives results that match with Fluent's 'line' if the environment variable CFDPOST_BOUNDARY_DATA_FROM_ELEMENTS is set to 1. However, a line in CFD-Post of type Cut gives results that do not match with Fluent's 'rake' because the former in infinite and the latter is clipped.

Streamlines

• Surface streamlines cannot be created on wall boundaries because wall velocities are zero.

  It is recommended that you create the streamline based on the Wall Shear vector. Ensure that Wall Shear is in the file; if it is not, return to Fluent and export that variable.

  Alternatively, you can use the near wall velocity for streamlines (and other plots) by setting CFDPOST_BOUNDARY_DATA_FROM_ELEMENTS before running CFD-Post.

• In the regions where the mesh is coarse and vector variable gradients are steep, streamlines in CFD-Post might hit walls earlier than similar streamlines in Fluent. This is due to a difference in computational methods, and can be avoided by refining the mesh.

• When creating Streamlines for Dual Cell heat exchanged Fluent cases, exclude Auxiliary Fluid domains from the Domains list because these domains can cause the streamlines to be terminated too early.

Turbo Workspace

• CFD-Post can initialize the turbo space only for domains that are enclosed with inlet, outlet, hub, and shroud regions. For more complex geometries, you must set up the problem such that the region of interest is isolated into a separate domain that can be initialized in CFD-Post.

• When choosing a report template for a Fluent turbo report, choose Release 12 templates (which do not have the word "Rotor" in the template name).

• Report templates that have "Rotor" in the name are from Release 11 and require variables that are not available from Fluent turbo files.

• For rotating machinery applications, identification of components and ordering, regions, rotation axis, number of passages, and interfaces cannot be done automatically; you must supply this information on the Turbo initialization panel. When generating turbo reports, select variables, instance transforms, and expressions will require manual updates; for details see Procedures for Using Turbo Reports when Turbomachinery Data is Missing.

• Also see "Velocity" in Quantitative Differences Between CFD-Post and Fluent.

Limitations in the Import and Display of Fluent Particle Tracks

• If particle track files from Fluent were written with rpvar dpm/io/cfd-post/export-int64? set to #t (default is #f), then, in order for CFD-Post to read the particle track files, you must have environment variable CFXPOST_READ_64BIT_FLUENT_PARTICLE_IDS set to 1.

• It is not possible to group or color transient particles by stream.

• The size of exported files and the intermediate history file is limited to 2 GB on architectures that have sizeof(long)==4 (for example: win64, ntx86, and lnx86).

• When Fluent particle tracks cross periodic boundaries, there will be a gap between the point on one side of the periodic boundary and the point on the other side. This is most visible if instancing is enabled, but appears only in transient cases.

• CFD-Post displays particle tracks as segments, whereas Ansys Fluent displays particle tracks as points. This is particularly shown by transient cases when viewing tracks for a particular timestep; CFD-Post displays tracks as segments of the track from the previous timestep to the current timestep, while Ansys Fluent shows points at the current timestep. Because of this, the range of the color variable will include data that is not included by Ansys Fluent when displaying particle tracks.

• Also see Exporting Steady-State Particle History Data in the Fluent User's Guide.

Polyflow Classic and FIDAP Limitations

• Some Polyflow Classic and FIDAP cases may have interior surfaces that are read into CFD-Post as boundaries. Unlike other boundaries, these "interior boundaries" cannot be used to create Polyline objects by intersecting them with a slice plane.

• CFX Results files generated by Polyflow Classic do not contain all the necessary information required for some automatic calculations in CFD-Post, including force and torque functions.

Limitations of Load Transfer to Mechanical

• In cases where forces on surfaces are transferred between Fluent and Mechanical, the forces displayed on the surface are read directly from the Fluent results file, while the forces on the corresponding Mechanical surface are averaged to the nodes. When viewed in CFD-Post, the values of the surface and Mechanical forces will not match.