preCICE-adapter for the CFD code ANSYS Fluent

Developed by Bernhard Gatzhammer

Go to tools/adapters/fluent
Create a subdirectory lnamd64/2ddp/ for serial execution and for parallel execution add a /2ddp_host/ and /2ddp_node/.
Put the libraries of preCICE and python2.7 (libpython2.7.so) into the lnamd64 folder.
Adapt src/makefile line 14 "SOURCES=...": There are several main udf files
- fsi_udf.c: For FSI simulations. Needs fsi.c.
- wave_profile_udf.c: For wave simulations with inflow profile. Needs wave_profile.c.
- wave_maker_udf.c: For wave simulations with moving wall. Needs wave_maker.c.
- fsi_and_wave_profile_udf.c: For FSI + wave simulations. Needs fsi.c and wave_profile.c. The variable SOURCES needs one one main udf file and the correspoding .c files.
Type: make "FLUENT_ARCH=lnamd64" to start the build. Add a "clean" to clean it.

2.1 How to start Fluent with GUI

start the binary "fluent" from your simulation folder
set double precision, processing options (serial or parallel) and the dimension (for parallel select also "show more", "parallel settings", "mpi types" -> open mpi

2.2 How to start Fluent without GUI

serial: fluent 2ddp -g < steer-fluent.txt
parallel: fluent 2ddp -g -t4 -mpi=openmpi < steer-fluent.txt (-t4 sets 4 processes for computations) (steer-fluent.txt drives Fluent, can also be done by hand)

Copy the lnamd64 udf lib folder to the simulation folder into /libudf/
Start Fluent and open the .msh or .cas file to be used
In Fluent, go to top menu Define->User Defined->Functions...->Manage... and load the libudf folder. The names of the udf functions should appear in the Fluent command line window. (only necessary if not yet included in the .cas file)
Define a function hook at Initialization. (see udf manueal, define -> user defined -> function hooks)
Define 1 user defined memory for the faces. (define -> user defined -> memory -> 1; adds one additional double to each face for precice face ids)

Perform the steps in 1.,2. and 3.
Set a user defined mesh motion according to function "gridmotions".
When the parabolic inflow profile is needed, you have to read it from file parabolic.prof, using the boundary conditions dialog box. Check, whether the number of points in parabolic.prof is way more than the elements at the inflow and that the velocities in the file are correct.

Go through the menus on the left and perform the following steps:

General: Set transient simulation and gravity in y-direction = -9.81
Models: Set Multiphase VOF explicit with Implicit body force formulation activated
Materials: Air and water-liquid (from Fluent Database) are needed
Phases: Name phases "phase-1-air" and set air as material, as well as "phase-2-water" with water as material
Cell Zone Conditions: Activate in operating conditions "Specified operating density" and keep default value.
Boundary Conditions:
- Set the top boundary to pressure outflow
- Set the left boundary to velocity inlet and set for Phase mixture the x- and y- velocity components to follow the corresponding UDFs, for Phase-2-water set the volume fraction UDF
Dynamic Mesh:
- Set the structure boundary to follow the UDF
- Set the domain to be deforming/remeshing as needed
Reference values: Only needed for writing output (since Fluent usese dimensionless values)
Solution methods:
- Set the PISO (pressure implicit) scheme and as volume fraction scheme the Modified HRIC scheme

Preparing the preCICE XML configuration:

The number of valid digits for the timestep length needs to be 8, since fluent has only a single precision timestep length. Set this in the tag <timestep-length ... valid-digits="8"/>

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