Updates to FF_PMF exercises

• Split the Readme into three readmes for the separate subexercises.
• for sub-exercises use ## as headline and for tasks ### to be consistent with other exercises
• Overview readme
  • More basic information in the top readme
  • referencing to excercise for main file, when stating the special differences for coupled setup
  • maybe include some short code snippets s.t. it is easier to follow and one does not have to switch force and back to the code for every single thing
• Task 1: interfaces
  • state some assumptions in readme (e.g. stationary, 2D, no gravity)
  • add to readme to check results with e.g. paraview if the applied changes make sense
  • make task stationary (no initAtPos() function needed, no "initial" output needed)
  • change permeability for BJS task1b so that things are actually visible (-> velocity does not change close to interface, why?)
• Task 2: models
  • state some assumptions in readme (e.g. transient, 2D, with gravity)
  • For task 2-A: Set the parameters to not write or plot any output when the task hasn't started yet
  • Fix the way in which the values.setState(2); is explained in the text. Not clear.
  • For evaluateWaterMassStorageTerm() in task 2.B: give a hint that volume is a property of the scv and porosity, saturation etc can be obtained through volVars (functions can be found in porousmediumflow/2pnc/volumevariables.hh header)
  • For evaluateInterfaceFluxes() in task 2.B: it should say molarMass instead of massFraction
  • maybe state explicitly how to run/call the python script python3 ./plotFluxes.py and that this script is reading the data stored in the flux_models_coupling.json-file
  • For task 2.C: update readme and input file to use VanGenuchtenPcLowSweThreshold and VanGenuchtenPcLowSweThreshold instead of outdated and not-used params pcLowSw and pcHighSw
  • as well the sentance "to look at how the regularization is set in the 2pspatialparams.hh" is not really up-to-date as the class VanGenuchtenDefault in material/fluidmatrixinteractions/2p/vangenuchten.hh is used instead of doing the regularization within the spatial params
  • For task 2.C: add TODO dumux-course-task 2.C in initialAtPos
• Task 3: turbulence
  • update text for saying which turbulence model is used: "...compositional zero equation turbulence model...", but the code snippet says "sstncmodel"
  • maybe give a short reference for the used model (dissertation/paper/book/website?) for interested people
  • For Task 3.A, when saying "Make sure your free flow problem inherits from the correct parent type:" and then introducing RANSProblem -> state before that k-\omega SST model is a specific RANS model. Otherwise the RANSProblem as a parent type appears from nowhere.
  • For Task 3.A: mention to change the NavierStokesBoundaryTypes to RANSBoundaryTypes (can be forgotten easily as just stated in code, but not in the intructions)
  • For Task 3.A: name the parameters k (turbulent kinetic energy) and \omega (specific turbulent dissipation rate) and give a hint where to find the names of the indices to set BCs (dumux/freeflow/rans/twoeq/indices.hh)
  • For Task 3.A: Change "set both variables on all walls to be dirichlet, except for the right boundary" to "set both variables on all free-flow boundaries to be dirichlet, except for the right boundary"
  • For Task 3.A: Change "then apply the ... variables to their primary variables in all locations" to "then apply the ... variables to their primary variables for the initial state in all spatial locations"
  • For Task 3.A: First boundaryTypes are adapted, then initial conditions are set and finally the boundary conditions are set. It would make more sense to set the boundary conditions for k and \omega directly after adapting the boundary condition types and after that adapting the initial conditions
  • For Task 3.A: Add that the parameter RANS.IsFlatWalBounded=True has to be added to the params.input as this parameter is required for using RANS models.
  • For task 3.A: Adapt this sentence "The result for the turbulent viscosity should look like this:" to "The result for the turbulent diffusivity should look like this:"
  • For task 3.B: maybe only use half of the FF domain in y direction to make advantage of symmetry BCs
  • For task 3.B: mention to look at results with paraview
  • For task 3.D: mention how velocity over y can be plotted with paraview and compared