Altair Virtual Wind Tunnel for ultraFluidX 2022 Release Notes


Virtual Wind Tunnel 2022 brings significant improvements when working with STL files and adds features towards the needs of aero-acoustics simulations.

Highlights include:
  • Improved performance with STL files
  • Higher frequency sampling through sub-time step support
  • User friendly output control with an updated microdialog and table view
  • Improvements to support fan noise simulations
  • Visualization support via HyperWorks CFD Post
  • Improved batch capability

New Features

Improved performance with STL files
A new, lightweight triangle-based model representation dramatically improves STL file I/O performance, especially for large models. Model import and load times are now twice as fast. Vwt/stmod file save time is three to four times faster for large model files. File sizes and application memory usage have been reduced to half the previous usage.
Benchmarks from a medium sized pickup truck model with 12 million triangles tabulated below summarizes the improvements:
  VWT 2021.2 VWT 2022 Improvement
Model Impot Time 66 30 2x faster
Memory Usage 4.3 GB 2.25 GB 0.5x usage
File Save Time 46 s 11 s 4x faster
File Size 250 MB 105 MB 0.4x usage
File Reload Time 50 s 22 s 2x faster
The performance improvements from VWT 2021.2 to 2022 across three different models are show below:
Model Description STL File Size Import Speed Up Save Speed Up Load Speed Up File Size Reduction Memory Reduction
Minivan 5.2 GB 2.38 3.82 2.97 2.44 1.8
Van 1.67 GB 1.84 2.30 1.14 2.30 2.0
Pickup 2.28 GB 2.20 4.18 2.27 2.38 1.9
Improved batch capability
Virtual Wind Tunnel can now be launched in batch mode with and without the GUI. Batch mode enables you to import a model, import and apply a full simulation template, and export simulation files. These output files can subsequently be run with ultraFluidX.


Higher frequency sampling through sub-time step support
ultraFluidX allows much finer output data from refined mesh regions in the form of fractional output intervals. These are now specified in floating point format. These are automatically rounded to the nearest supported fractions. A new microdialog shows the output interval specified as 0.25 below that corresponds to the fraction ¼. The corresponding physical frequency is also shown as a visual aid.

Figure 1.
Improved output control
Post-processing data output controls now allow unit-based inputs, in addition to solver-based iterations. Start time for recording outputs can be specified in physical time or solver iterations. High frequency sampling via sub-time steps is supported through three input choices:
  • Fractional output intervals
  • Mesh refinement levels
  • Frequency-based input
As shown previously, the microdialog for outputs has been enhanced so you can select your preferred input mode. Choosing the clock icon on the top left will allow you to a input start time in seconds, as shown below. Instead of fractional output interval, you can specify the mesh refinement level by selecting the mesh icon in the left center to set the correct fractional output interval.

Figure 2.
Alternatively, you can select the Hz icon to directly specify your preferred sampling frequency in Hertz. This input is automatically rounded to the closest fraction supported by the solver and mesh refinement level. The actual sampling frequency and fractional output interval are shown right below the user requested target frequency.

Figure 3.
While all outputs support this new microdialog design, monitoring surface has a subtle difference. Since it doesn’t support fractional output intervals, calculations are rounded to whole numbers and mesh refinement level selector is unavailable. In addition, it uses a drop-down menu to select Visual and Summary output modes. Previously, the Visual and Summary outputs were stacked one below the other.

Figure 4.
The Output Table view allows you to work with all this information in the same window. Multiple outputs can be selected in this view which makes bulk changes easy to perform.

Figure 5.
Simulation mode to support Fan Noise simulations
A simulation mode has been introduced in the Run dialog that can be used to indicate you are performing a fan noise simulation. This tells the ultraFluidX solver to automatically reconfigure default settings from external aerodynamics to fan noise and saves the user from having to do them manually.
Smooth ramp up for fans
The simulation can now be smoothly ramped up with user specified iterations in the Run dialog. This smoothly increases the fan rotation speed and inflow velocity for the Wind Tunnel.

Figure 6.
Support for precision and scientific notation for Probe output data
As part of enhancements needed to improve fan noise simulations, probe output data is now written out in scientific notation and the output data precision has been increased to eight significant digits. You can override these settings in the Output Controls panel.
Improved default settings
The default window-averaging window size is now computed as a function of inflow velocity and object length.

Figure 7.
Visualize results with HyperWorks CFD Post
The uFX results files can now be visualized in HyperWorks CFD Post. The Show Analysis button will prompt you to select *.case or *.sos files that are then loaded into HyperWorks CFD Post. HyperWorks Desktop will need to be installed separately for this to function seamlessly. This replaces Fieldview which is no longer available from within Virtual Wind Tunnel.

Figure 8.
Support for binary STL files
Binary STL files can now be imported into Virtual Wind Tunnel. Note that binary STLs do not support multiple parts or names in a single file. All triangles in a single binary file are imported as a single part.

Known Issues

The following known issues will be addressed in a future release as we continuously improve performance of the software:
  • Modifying units on importing STL/NAS files.
  • In rare occasions selecting the split intersected parts advanced option for a fan overset mesh volume can cause errors.

Resolved Issues

  • Divide by zero errors are protected in case of zero inflow velocity.
  • Run settings are saved correctly in the *.vwt database format.
  • Probes created on overset volume no longer gets transformed into Point objects.
  • Gap finder tool has been removed.