Altair Flow Simulator 2025 Release Notes

Highlights

  • Flow Simulator API
  • GUI dark mode
  • Solver accuracy improvement for real gasses

New Features

Flow Simulator API
The Flow Simulator solver can now be run from a user-defined program using a set of functions to load and run a Flow Simulator model. A dynamic link library (DLL) file containing the Flow Simulator solver can be linked to a user-defined program. Several simple functions are available so that the user-defined program can interact with the Flow Simulator model: FS_LOAD_MODEL, FS_RUN_MODEL, FS_GET, FS_SET, and FS_END. C, C++, and Fortran programing languages have been tested and examples are supplied with the Flow Simulator installation (<install_directory>/FlowSimulator/Resources/Solver_API_Examples).
GUI Dark Mode
The Flow Simulator GUI display can be toggled to dark mode. The dark mode uses a black background with lighter text colors.


Figure 1. GUI Dark Mode

Enhancements

Solver Accuracy Improvement for Real Gasses
Since version 2022, Flow Simulator has used the compressibility factor, z, to adjust the ideal gas relationship for density. The compressibility factor improves the accuracy for fluids that are at pressures and temperatures where they do not behave like an ideal gas.
In version 2025, Flow Simulator has an improved accuracy option for fluids that do not behave as an ideal gas. This new approach uses modified exponents for the isentropic equations. It still uses the compressibility factor as before. As before, only fluids using Coolprop can model the real gas effects. Most, but not all elements, have been updated. See convhist_fi.out for a warning message if the model uses an element that has not been updated.


Figure 2. Real Gas Gammas
Text Magnified During Hover
An object’s text can be magnified temporarily when the mouse pointer is on the object. This is useful if the text size is too small to read at the current zoom level or model scale. You can toggle this behavior in the User Settings.


Figure 3. Text Magnified During Hover
Fan, Compressor, and Turbine Efficiency Calculations
The total temperature exiting a fan, compressor, or turbine is a function of the total pressure change and polytropic efficiency of the component. The calculation methods have been updated to consider real gas effects. If real gas effects are required, the Schultz or Small Step method should be used for an accurate exit temperature. The Small Step method is the most accurate but can also increase solver run times. The Schultz method is less accurate but is fast. The “Auto” method is the default. It uses the standard ideal gas equations for ideal gasses and the Schultz method for real gas. Coolprop must be the fluid property source for the Schultz and Small Step methods.


Figure 4. Fan, Compressor, and Turbine Efficiency
Heat Transfer Coefficients (HTC) for Rotating Cavities
Four new HTC correlations for rotating surfaces have been added. These correlations are useful for rotating machines such as gas turbines and electric motors.
  1. Rotating Cavity Using Duct Flow: Uses the Dittus-Boelter duct flow correlation for general cavities with rotating flow and surfaces.


    Figure 5. Rotating Cavity Using Duct Flow
  2. Rotor Disk with Bore Flow: Correlation for cavities typically found in gas turbine compressors. Use correlation on rotating disk surfaces with axial flow at the bore. The correlation can be used with convectors and is based on the paper by P.R. Farthing.


    Figure 6.
  3. Free Rotating Disk: Use this HTC correlation on an isolated rotating disk. An isolated disk has no through flow, other than the flow induced by the disk rotation, and the far field ambient fluid has no swirl. The correlation can be used with convectors.


    Figure 7.
  4. Free Rotating Cylinder: Use this HTC correlation on the inner or outer surface of a rotating cylinder. The correlation can be used with convectors.


    Figure 8.
Thermal Node and Flow Chamber Rotor Index Color Plot
From the GUI, you can now plot color contours of the Rotor Index for thermal nodes and flow chambers. From the color contour panel, use the Rotation Rotor Index option. Use this to quickly check model inputs.


Figure 9. Rotor Index Color Plot
Color Cavity Surface by Force Direction
From the GUI, you can now color the cavity surface lines by the force direction. Use this to quickly check the surface axial force direction input.


Figure 10. Color Cavity Surface by Axial Force Direction
Advanced and Incompressible Tube - New Inlet Head Loss Options
The advanced and incompressible tube elements now have head loss options for abrupt transition, rotating annulus, and rotating parallel tube. You can combine the abrupt transition loss with the rotating annulus or rotating parallel tube.


Figure 11. New Inlet Head Loss Options for the AT and IT
Advanced Tube - New Friction Option
The advanced tube has a new wall friction option for a rotating tube that is offset and parallel to the rotation center line. It is based on a paper by Johnson.


Figure 12. AT new Friction Option
Automatic Area Option for Several Elements
The amount of user input has been reduced by introducing an automatic area option for several elements. This option only works if an element is attached to a single element upstream and downstream that has a specified geometry (area or diameter). Two elements that use the automatic area option cannot be attached to the same fluid chamber. The automatic option is now the default for these elements. The areas are extracted at solver run time. Check the *.res file for areas used for the element.


Figure 13. New Automatic Area Retrieval Options
Orifice Plate Element Grill K Loss
New K loss options have been added to the Screen subtype of the orifice plate element. These options use a K loss based on the ratio of the free (or open) area to the pipe area. The losses are different if the grill is at the inlet (from ambient to the pipe) or the exit (from the pipe to ambient).


Figure 14. Grill K Loss for Orifice Plate Element
Automatic Flow Equation (Fluid) Type for Element
Most elements have flow equations for compressible gas and incompressible liquids. The type of equation used can now be automatic and based on the fluid entering the element. Compressible gas elements are used for gases such as air, while the incompressible liquid options are used for liquids, such as water. The benefit of the automatic option is for models that may have phase change or if the fluid phase is not known before the run. Elements with the automatic flow equation option include: valves, transitions, bends, junctions, elevation, and orifice plate.
Note: The orifice elements automatically use incompressible equations if a liquid is entering the element.


Figure 15.
Generic Fixed Volume (GFV) Accumulator Improvements
Two changes have been made that make it easier to use GFV accumulators to represent the fluid volume of piping systems for transient analysis. The first change is the option to convert a momentum chamber to a GFV. The automatic element creation tool creates momentum chambers. The new change makes it easy to convert these to GFV. The second change is the option to use the volume of the attached elements instead of a user-supplied volume. This option uses half the volume of all elements attached to the GFV. Only elements that have geometry information to calculate a volume are valid: tubes, conical transitions, and bends. The *.res file contains the volume found in the attached elements.


Figure 16. GFV Accumulator Improvements
Element and Resistor Connections
Version 2024.1 introduced the option to change the element and resistor connection chambers (and nodes) in the Property Editor. Now, the connecting chambers (and nodes) can be selected from the modeling window.
Note: The Element Connections tool will be deprecated in the future.


Figure 17. Element and Resistor Connection Edits

Known Issues

The following known issues will be addressed in a future release as we continuously improve performance of the software:
  • Some very large models or models using a small screen unit (like millimeters) can have text that is too small to read. The maximum size of 80 may be too small. Using a different screen unit may allow for larger text.
  • Visibility of some items in dark mode will be improved in future releases.

Resolved Issues

  • GUI problem with the tube element bend table always changing to four bends when edited.
  • GUI crash in the Customization Manager.
  • Problems with the GUI Goal Seek tool not using the number of streams when using flow rate as the target.
  • GUI problem for controllers using linear relationships.
  • GUI problem when copying items that are in a flow group.
  • GUI problem when creating elements directly from geometry. The GUI creates less short tube elements and uses the screen unit for radius limits.
  • GUI now sets the screen unit to the unit of the geometry file when reading for the first time.
  • The GUI text for the vortex element flow flag is now more descriptive for the option that uses another flow element.
  • GUI problem with the arrowhead sizes after multi-editing resistor connections.
  • GUI problem with the defaults for drop-down lists in the Analysis Controls.
  • GUI problem with units of Tube Station coordinates.
  • Updated Coolprop from version 6.4.3 to version 6.6.