Frequently Asked Questions

Frequently Asked Questions SimFlow CFD Software

01What are the limitations of the Free version compared to a commercial license?

The Free version includes the same solvers and physical models as the commercial plans and has no time limit. It has the following limitations:

  • the mesh size is limited to 200,000 nodes,
  • no parallel meshing or computing (1 CPU only),
  • cases cannot be imported or exported.

Commercial licenses remove all of these limitations. The plan comparison on our website shows the details.

02What does the 30-day trial include, and how is it different from the Free version?

The Free version has no time limit, but it is limited to 200,000 mesh nodes and 1 CPU for meshing and computing. The 30-day trial gives you access to all SimFlow features: unlimited mesh size, unlimited CPU cores and parallel computing. After 30 days, the software reverts to the Free version. Use the trial request form to request a trial.

If you need more time to evaluate SimFlow on your own case, please contact us before the trial ends.

03What kind of license do you offer?

You can choose between a Single Seat license, bound to one computer, and a Floating license, which can be used on any computer in your network, one at a time. Licenses are offered as an annual subscription. Perpetual licenses are also available. A perpetual license includes one year of maintenance (updates and support) with optional yearly renewals. Plans and prices are listed on the pricing page on our website.

Universities and research institutions can get special pricing. Please contact us for details.

04Can several people share one license, for example in a university lab or an engineering team?

Yes. With a Floating license, the license is installed on a license server in your network and can be used from any computer in that network. Each floating license can be used by one user at a time. This user can run several SimFlow instances on one computer. If more people need to work at the same time, you need more floating licenses on the server.

The License Server application runs on Windows or Linux. It is included in the SimFlow installation package for Windows and Linux. A separate License Server installer for a dedicated server is also available on request. Each client computer connects to the license server in the License panel. If the connection to the license server is lost, SimFlow continues to work as the Free version until the license is available again.

05Does SimFlow require an internet connection?

With the default license, SimFlow connects to the internet only to validate the license. No user or project data is sent.

We also offer license versions that can be used on computers without network access. This option is agreed with the customer at the time of purchase.

With a Floating license, the situation is the same, but it applies only to the license server. The license server must be installed on one of the computers in your organization.

Please contact us if you need more details.

06What will happen after my SimFlow license expires?

After the licensing period expires, you can renew your license or use SimFlow as the Free version. Cases with a mesh larger than the Free version limit open in Viewer Mode, which is shown in the window title. In Viewer Mode, you cannot run computations or save the case, but you can view its settings and results.

07How do I know that I am running SimFlow in the commercial mode?

Look at the SimFlow logo. In the Free version, the remark Free Version is shown below the SimFlow logo. When this remark is not shown, your license has been detected by SimFlow, and the limitations of the Free version do not apply to you. The SimFlow Launcher also shows your license type and its features in the License panel.

08Can I use the Free version of SimFlow during classes at the university for teaching?

Yes. The Free version is intended for learning CFD and SimFlow, for teaching, and for evaluating and testing the software, so it is a good fit for classes. If your classes need larger meshes or parallel computing, we offer special pricing for universities. Please contact us for details.

01I am trying to install SimFlow on Linux, but it does not recognize the executable file, which I downloaded. Why?

During SimFlow installation on Linux, a few additional actions may be required from the user. Most often, you have to make the downloaded file executable. See the Linux installation guide for details.

02When I attempt to download SimFlow, I get the error message 'Signature corrupt or invalid'. Why?

Most likely this problem is caused by a bug in Microsoft’s web browser, which incorrectly interprets a valid certificate as corrupt or invalid. In order to avoid this problem, please use a different web browser when downloading the SimFlow installation package.

01Which geometry CAD file formats are supported by SimFlow?

Currently, SimFlow supports the following formats:

  • *.STL
  • *.OBJ
  • *.STEP
  • *.STP
  • *.IGES
  • *.IGS
  • *.BREP
  • *.DAT (airfoil profile)
02Can I import a mesh or a case created in other software, for example Fluent or CFX?

You can import meshes in the Import panel. The supported formats are:

  • Fluent: *.msh (ASCII)
  • Ansys: *.cdb, *.ans
  • I-DEAS: *.unv
  • Gambit: *.neu
  • Gmsh: *.msh
  • CFX: *.geo (CFX version 4 format)
  • native OpenFOAM meshes

For some formats you can specify the mesh units, so that the mesh is scaled automatically during import.

Only the mesh is imported. Boundary conditions, materials and solver settings have to be defined in SimFlow.

03It seems that SimFlow did not recognize that the geometry which I imported was created in millimeters, and it is 1000x greater in SimFlow. How can I deal with it?

SimFlow uses SI units, so the dimensions of the geometry must be in meters. Units are not saved in some CAD formats. If you have not created the mesh yet, scale the geometry:

  1. In the Geometry panel, right-click on the imported geometry name.
  2. Use the Scale option.

If you have already created the mesh, scale the mesh instead:

  1. In the Mesh panel, right-click on the default region.
  2. Use the Scale option.
01Can I simulate conjugate heat transfer and cooling problems, for example electronics cooling or heat exchangers?

Yes. Conjugate heat transfer (CHT) between solid and fluid regions is available in all SimFlow plans, including the Free version. Use the chtMultiRegionSimpleFoam solver for steady-state cases and chtMultiRegionFoam for transient cases. A CHT case requires a separate mesh region for each solid and fluid part. See how to create mesh regions for details.

Good starting points are the Electronics Cooling, Heat Exchanger, Cooling Channel and Cylinder Cooling tutorials, as well as the Heat Transfer at Pipe (CHT) validation case.

02Can SimFlow simulate solid particles or droplets carried by a fluid?

Yes. SimFlow offers Lagrangian particle tracking solvers, for example DPMFoam, which accounts for the particle volume fraction and particle collisions (dense particle flows), and MPPICFoam, which uses the Multiphase Particle-in-Cell method. Both handle laminar and turbulent flows of Newtonian and non-Newtonian fluids.

For dilute particle or droplet clouds in multicomponent and reacting flows, you can use the species and reactions solvers with Lagrangian parcels, for example:

Particles are introduced into the domain with injectors defined in the Discrete Phase panel: a Cone injector representing a nozzle, a Boundary injector, or a Manual injector at specified locations. See the Cyclone Separator tutorial for a complete example.

03How should I model rotating parts such as fans, impellers or rotors: MRF or a moving mesh?

Both approaches are available. The Multiple Reference Frames (MRF) model, defined in the Cell Zones panel, lets you solve a steady-state problem with a rotating frame for the rotor and a stationary frame for the rest of the domain. It is an approximation, but when there are no significant interactions between rotating and stationary parts, it gives sufficient accuracy at a relatively low computational cost (see the Marine Propeller tutorial).

When the rotor-stator interaction matters, use a transient simulation with a moving mesh defined in the Dynamic Mesh panel and a sliding mesh interface (cyclicAMI). See the Mixing Tank tutorial for an example. This approach is more accurate but considerably more expensive.

Another option for moving bodies is an overset mesh. An overset (Chimera) mesh is a separate mesh around the moving body that overlaps a background mesh and moves with the body, so large motions are possible without deforming the mesh. SimFlow supports overset meshes, for example with the overPimpleDyMFoam solver.

04Can I simulate non-Newtonian fluids?

Yes. For incompressible solvers, the viscosity model is selected as the Transport Model in the Transport Properties panel. The available models are:

  • Newtonian
  • Power Law
  • Cross-Power Law
  • Bird-Carreau
  • Herschel-Bulkley
  • Casson

See the Blood Flow tutorial for an example.

05How can I model filters, perforated plates, packed beds or other porous regions?

Use the Porosity model in the Cell Zones panel. It adds flow resistance in a selected cell zone, so small structures that would be impossible to resolve with the mesh do not have to be modeled explicitly. Two models are available: Darcy-Forchheimer and Power Law. Model coefficients are specified in a local coordinate system (Cartesian or cylindrical), which allows anisotropic resistance.

01Which units of physical quantities are used in SimFlow?

SimFlow uses OpenFOAM ® solvers, and therefore you must use SI units. It is important to remember that it also applies to the dimensions of the geometry, which must be scaled to meters.

02I am simulating incompressible flow using an incompressible flow solver. Why do I have to specify pressure values in a strange unit instead of Pa?

Incompressible flow solvers in OpenFOAM ®, and thus in SimFlow, operate using a kinematic pressure instead of a physical pressure in order to compute the Navier-Stokes equations without explicitly showing the constant fluid density in the equation.

Kinematic pressure is defined as pressure divided by fluid density, and it is expressed in \([m^2/s^2]\). Always input kinematic pressure values when using incompressible flow solvers in SimFlow to obtain correct results. When you analyze the results, remember that the pressure field in ParaView displays values of kinematic pressure. Therefore, you must multiply the values of kinematic pressure by the fluid density in order to calculate the pressure field expressed in \(Pa\). Read more about kinematic fluid properties on the SimFlow website.

03Forces acting on the geometry calculated during the simulation are way off what I expected. Did I do something wrong?

There are three main possibilities for incorrect values of forces:

  1. Your model was created in units other than meters.
  2. In the case of incompressible solvers, you need to multiply displayed values of monitored forces by fluid density.
  3. In SimFlow, as in OpenFOAM ®, even 2D meshes are computed as 3D meshes, so the forces shown correspond to the mesh thickness. To get the force per unit length for a 2D case, in \(N/m\), divide the result by the mesh thickness.
04What are the calculation methods of forces and force coefficients that can be monitored?

Forces are calculated by integrating the stress tensor over the selected boundaries, so they include both the pressure and the viscous contributions. You select these boundaries in the Forces tab of the Monitors panel. Because forces are monitored on mesh boundaries, it is worth creating a separate boundary (patch) for the surface where you want to monitor forces when you prepare the mesh.

If you select the Monitor Coefficients checkbox, the values of forces are divided by the reference area and reference dynamic pressure. Results of this operation correspond to force coefficients, and they are shown in the graph instead of values of the forces.

05The Mesh button is disabled and I cannot remesh the geometry. How to solve this problem?

The Mesh button is disabled if you have result files in your case directory. Results are always tied to the mesh they were calculated on, so deleting them has to be a deliberate step before you remesh. To delete the results, go to the Run panel and click the Reset Simulation button. Then you can remesh the geometry.

06I want to simulate a conjugate heat transfer problem, but solvers appropriate for this purpose are disabled in the list of available solvers. Why?

Conjugate heat transfer solvers require at least two mesh regions, in any combination of fluid and solid regions. For example, a case can have two fluid regions separated by a wall, or several solid regions with different material properties. Therefore, these solvers can be selected only after you create a mesh sub-region.

A mesh created in SimFlow is stored in the default region. To create a mesh sub-region:

  1. Create the mesh.
  2. In the Mesh panel, right-click on the default region and choose Make sub-region.
  3. Move the Point to a location inside the other region and create a mesh for it.

Then you can select one of the conjugate heat transfer solvers.

07I can’t calculate Wall Heat Flux, because the button in the Postprocessing panel is disabled.

Wall heat flux currently can only be calculated for compressible solvers. If you are using the Boussinesq approximation, this option will not be available as well.

08I constantly get a nan error in the SimFlow console. Why?

If you can see a line in the SimFlow console similar to:

smoothSolver: Solving for Ux, Initial residual = nan, Final residual = nan, No Iterations 1000

or another line containing the word "nan", it means that your simulation diverged. Divergence is usually caused by the simulation settings, for example mesh quality, a time step that is too large, boundary conditions or numerical schemes. To run the simulation again with corrected settings:

  1. Click the Reset Simulation button in the Run panel.
  2. Check the mesh quality, time step, boundary conditions and numerical schemes, and correct them where needed.
  3. Run the simulation again.

If the problem persists, send us your case so we can take a look.

09Why are my results different from the ones in the video tutorials?

There are a few possible reasons for this. Please check again step-by-step whether you correctly set up your simulation. If you cannot find a problem with your simulation settings, small differences may come from differences between OpenFOAM ® versions and default numerical settings in SimFlow, which can also vary between SimFlow versions. If you still need help, send us your case and we will take a look.

01Which version of OpenFOAM® is supported by SimFlow?

SimFlow aims to support the latest OpenFOAM ® versions. New SimFlow releases with an updated OpenFOAM ® version usually come out once a year, and sometimes every two years when OpenFOAM ® changes little between versions. Check which OpenFOAM ® versions are supported by different versions of SimFlow.

02Can I use both single-precision and double-precision OpenFOAM® solvers with SimFlow?

Yes, you can if you have single-precision or double-precision OpenFOAM ® compilation. It requires setting a proper path to the OpenFOAM ® directory in the SimFlow launcher settings.

03Which OpenFOAM® distribution does SimFlow work with?

SimFlow 5.1 works with the OpenFOAM ® releases from openfoam.com, developed by ESI-OpenCFD. These releases are named after the year and month of release, for example OpenFOAM ® 2512, which is the recommended version for SimFlow 5.1. SimFlow supports this line of OpenFOAM ® on an ongoing basis. The list of supported versions shows which releases work with each SimFlow version.

04Can I open an existing OpenFOAM® case in SimFlow?

Yes. You can import an OpenFOAM ® case packed in a ZIP archive into a SimFlow workspace. To import a case in the SimFlow launcher:

  1. Expand the options menu next to the New button and select Import Case.
  2. In the File (zip) field, select the ZIP archive with the case.
  3. Choose the target Folder, enter the Case Name and click the Import button.

The archive must contain the system/controlDict file. When you open the case, SimFlow reads the solver from controlDict, as well as the mesh, the case dictionaries and the field files. The solver must be one of the solvers available in SimFlow. Check the settings in each panel before you run the simulation.

Case import is available with paid licenses and is not included in the Free version.

05Can I export a SimFlow case to the native OpenFOAM® format?

Yes. SimFlow exports a case as a ZIP archive with the OpenFOAM ® case files. To export a case:

  1. In the top menu, select Case > Export Case (ZIP).
  2. Choose the target system and whether to include results and logs.
  3. Press OK and save the ZIP file.

Case export is available with paid licenses and is not included in the Free version.

01Which files should I include when sending a sample case?

If you have a problem with your simulation, export the case to a ZIP file:

  1. In the top menu, select Case > Export Case (ZIP).
  2. Make sure that Include Results is unchecked.
  3. Press OK and save the ZIP file.

If SimFlow itself does not work as expected, you can also send us diagnostic information:

  1. In the top menu, select Help > Send Diagnostics.
  2. Enter your email address in the My e-mail address field.
  3. Press Send to Support Team.

The diagnostic information contains your system and SimFlow configuration, the console output and the program logs. It does not contain your case files. You can also press Download ZIP to save this information on your computer.

Please do not send large files as email attachments, as we may not receive them due to technical limitations. Please contact us through the contact form on the SimFlow home page.

02Where can I find training materials?

Training materials dedicated to SimFlow are available in the form of User Guides, Tutorials for general understanding of the software and Documentation for single feature descriptions.

If you wish, we can customize training materials for your specific needs. Send us a quick note and we will get back to you with possible solutions.