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How to Create ROM for Transient Fluid Simulations in Fluent?

    • Zeyang Jiang

      I am currently working on transient fluid simulations using ANSYS Fluent, and I'm interested in using Reduced Order Models (ROMs) to reduce computation time and potentially create digital twin models. However, I've learned that Fluent's ROM Builder is primarily designed for steady-state simulations. What are the recommended approaches or alternative methods for creating ROMs in the context of transient fluid simulations? I would appreciate any insights or guidance on this matter.

      Specifically, I would like to know if there are any tools or techniques that can be used to build ROMs for transient simulations in Fluent, or if there are alternative software packages that are better suited for this purpose. Any tips or best practices in creating ROMs for transient fluid dynamics would be highly valuable.

      Thank you for your assistance!

      Additional Context:

      • I am working on a project involving time-varying flow phenomena.
      • I have experience with Fluent's ROM Builder for steady-state simulations.
      • I am open to exploring other simulation software if it offers better support for transient ROMs.
      • Any relevant research papers or resources on this topic would also be greatly appreciated.

    • SRP
      Ansys Employee


      I suggest you to check fluent beta feature manual : 19.1. Manual Production of ROM Files from Stand-Alone Fluent (ansys.com)

      And and fluent use's guide: Chapter 34: Creating Reduced Order Models (ROMs) (ansys.com)

      Hope this helps you.

      Thank you.



      • Zeyang Jiang

        Thank you for the information!

    • Edward Carman


      There are generally three ROM methods that can be applied to dynamic problems, depending on the problem type:

      1. Linear Time Invariation (LTI) ROM - applicable to systems whose behaviour satisfies the linear and time-invariant assumptions. Typically this is applied to conduction-only thermal problems e.g. forced-cooled systems where the flow field is a assumed to be constant and only temperature varies. This would cover applications like battery packs are power electronics.
        These are built by sequentially applying step inputs
      2. Linear Parameter Varying (LPV) ROM - applicable to systems whose behaviour is nonlinear, but could satisfy the linear and time-invariant assumptions if one of the input parameters was fixed. Typically this applied to similar applications as LTI, but where the cooling flow rate varies e.g. battery packs or power electronics with a varying flowrate going into the cooling plate.
      3. Nonlinear Dynamic ROM - general nonlinear dynamic systems. Applied to nonlinear dynamic applications whose behaviour is well outside the range of the LTI and LPV assumptions. These could be systems with significant radiation or natural convection or other forms of nonlinearity.
      All three methods can build ROMs based on point probe (scalar / 0D) or full field (vector / 3D) data. To generate scalar training data, you can simple export report plots to .csv files. There is also an add-on package on the Customer Portal called 'ROM Builder Preprocessing for Fluent'. This automates some of the scalar data export and is also the preferred method for 3D data export (both for static and dynamic ROMs).
      The ROMs themselves are built using Ansys Twin Builder (installed as part of the AEDT installation package).
      Some documentation for the Dynamic ROM can be found here:
      The LTI and LPV wizards are accessed under Toolkits:
      There are also examples included with the installation under "\Win64\Examples\Twin Builder\Applications" e.g. "C:\Program Files\AnsysEM\v232\Win64\Examples\Twin Builder\Applications"
      • Zeyang Jiang

        Thank you for providing this detailed information regarding the three different Reduced Order Model (ROM) methods for dynamic problems in ANSYS, as well as the resources and tools available to create these ROMs.

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