28.1. Overview and Limitations

Intrinsic fluid-structure interaction (FSI) capabilities allow you to simulate either one-way or two-way FSI problems completely within a Fluent session. One-way FSI problems assume that only the fluid side will have an impact on the solid side through the fluid force that acts on the structure. Since there is no feedback information from the solid side, for one-way FSI simulations you can either compute the fluid flow and structural deformation simultaneously, or compute the structural side independently after the fluid simulation is completed. However, if the solid domain influences the fluid side of the FSI simulation, then you must model it as a two-way FSI simulation by enabling mesh motion for the fluid domain through a dynamic mesh.

The solution of an FSI problem requires the solution of both the fluid flow problem as well as the structural problem. The solution of the structural equations is limited by following:

  • The structural model only supports the following cell types: in 2D, quadrilateral and/or triangular cell types; in 3D, hexahedral, tetrahedral, wedge, and/or pyramid cell types. The structural model does not support polyhedral cells. This applies only to the solid zones.

    Note:  If you use the meshing mode of Fluent to generate a hexcore mesh, the resulting mesh will not be suitable for the structural model, as such meshes contain small numbers of polyhedral cells.

  • You are not allowed to replace the mesh once an FSI solution has been initialized and/or started. This is due to the fact that the new mesh will be partitioned and the subsequent data migration is not supported in FEA cases. Re-partitioning fluid zones is allowed, however, since it does not affect solid zone partitioning.

  • The fluid and solid zones must be separated by two-sided walls (that is, wall / wall-shadow pairs).

  • At least one solid zone must be present in the domain in order to enable the structural model.

  • The following dynamic mesh options are not supported for intrinsic FSI problems:

    • In-Cylinder

    • Six DOF

    • Contact Detection

  • The Intrinsic FSI type can only be selected in the Dynamic Mesh Zones dialog box for the side of a two-sided wall (that is, the wall or wall-shadow) that is immediately adjacent to the fluid cell zone (as indicated by the Adjacent Cell Zone field in the Wall dialog box).

  • For a wall that is adjacent to a solid zone or between a solid and fluid zone:

    • The only user-defined functions (UDFs) that are supported for displacement and force are DEFINE_SOURCE_FE, DEFINE_WALL_NODAL_DISP and DEFINE_WALL_NODAL_FORCE, respectively (as described in DEFINE_WALL_NODAL_DISP and DEFINE_WALL_NODAL_FORCE). All other boundary condition profiles or UDFs (such as DEFINE_PROFILE) will produce an error message.

    • The Shell Conduction option is not supported.

  • The structural model is not compatible with:

    • mesh adaption

    • the mesh morpher/optimizer

    • British or centimeter-gram-second (CGS) units

    • FMG initialization

    • adaptive time stepping

  • The structural model is not available when running Fluent under Ansys Workbench.

  • The Linear Elasticity structural model is only appropriate when the stress loading does not exceed the yield strength of the solid material.

  • The Linear Elasticity structural model is compatible with the 2D Axisymmetric or Axisymmetric Swirl option.

  • Postprocessing variables related to structures and the Structural Model are only available on solid cell zones. Therefore, any computations made on variables available under Structure... should only include solid zones to ensure they are evaluated correctly.

  • For solid structural solutions, there is no special treatment for periodic boundary conditions. The structural solver will treat such boundary as stress free.