Tutorial: perpendicularFlap

This tutorial demonstrates a two-dimensional fluid-solid interaction between a steady channel flow and a rigid flap that protrudes perpendicularly from the lower wall. The fluid is incompressible and Newtonian (rho = 1, nu = 1) with a uniform inflow of (10, 0, 0) m/s. The solid is a linear-elastic flap (rho = 3000 kg/m³, E = 4e6 Pa, nu = 0.3) that is free to rotate about its fixed root and lies on the flap interface patch. The frontAndBack patch is marked empty, so the simulation is purely two-dimensional.

The coupling interface uses solidPatch interface and fluidPatch flap, while the kinematic and dynamic conditions are enforced by the partitioned solids4Foam solver. Strong coupling occurs early in the unsteady response, which is why most benchmarking focuses on the first second of the simulation, even though the control dictionary extends to t = 10 s.

Coupling options

This case ships with a tuned IQNILS configuration as the default (./Allrun). The new Allrun script can also run the original Aitken under-relaxation scheme and control whether the solver runs serially or in parallel:

  • ./Allrun (default): IQNILS coupling.
  • ./Allrun aitken: original Aitken relaxation scheme.
  • ./Allrun parallel: run in parallel (can be combined with either coupling option).

The script uses foamDictionary to update constant/fsiProperties on the fly and resets the dictionary back to the IQNILS default after the run. This means you can easily reproduce either algorithm without manually editing dictionaries.

Running the case

  1. Source your OpenFOAM environment (so that solids4Foam and foamDictionary are on PATH) and ensure PETSc is available.
  2. Optional: reduce system/controlDict → endTime to 1.0 if you only want to probe the strongly-coupled transient window.
  3. Run ./Allrun [coupling] [parallel].

solids4Foam will build the solid and fluid meshes, execute the coupling loop, and, if requested, run in parallel with automatic decompose/reconstruct steps.

More background on the available coupling methods and fluidSolidInterface options can be found in src/solids4FoamModels/fluidSolidInterfaces/README.md.