Getting started

[AndreWeiner]

Hi @JihooKang-KOR,

to get started with this project, I suggest the following:

• study the flat plate test case carefully and execute it as described in the main README.md
• improve the description of the test case in test_cases/turbulentFlatPlate/README (what happens in the Allrun script? Which function objects are executed? What is the purpose of the test case?)
• add a function object to write out the residuals as described here; plot the initial residuals against the iterations
• use Markdown syntax such that the description will be rendered properly on Github
• create a Jupyter notebook for visualizing the results instead of using the plot script
• in fvSolution, the SIMPLE solution control is currently commented out; use the solution control and check how the tolerance affects the results

If questions come up, feel free to use this issue to discuss them.

Best, Andre

[AndreWeiner]

Hi @JihooKang-KOR,

a couple of minor comments on the latest commits:

• when you write the commit message, please mention the associated issue; for example: Add Jupyter notebook for plotting residuals; related to issue #1.; the commit is then automatically attached to this issue, and I get notified
• the resulting matplotlib plots look better with the following tricks

  # increase dpi and use latex rendering; include once at the beginning of each notebook
  import matplotlib as mpl
  mpl.rcParams['figure.dpi'] = 160
  mpl.rc('text', usetex=True)
  ...
  # typical figure with one subplot
  fig, ax = plt.subplots(1, 1, figsize=(8, 3))
  ax.plot(..., label=r"$c_f$")
  ax.set_xlabel(r"$\tilde{x}$")
  ...
  # tight layout for saving as PDF
  plt.savefig("output/example.pdf", bbox_inches="tight")

Good work so far!

Best, Andre

[AndreWeiner]

Hi @JihooKang-KOR, I just finished checking the latest commits. Really great job! Everything nicely scripted and documented.

Regarding the results, I was surprised that the kink in the friction coefficient for small x-values did not disappear when switching off the wall functions. If you open the results with ParaView, you can see oscillations in the p and U fields. The kink in the shear stress is very likely related to those oscillations.

I tested a couple of changes in the settings and found sensitivity to the divergence scheme for U (entry grad(phi,U) bounded Gauss linearUpwind grad(U); in fvSchemes). I would like to investigate this issue further before moving on to the wall modeling.

Could you test how the following divergence schemes affect the friction coefficient and the oscillations?

// to compare
div(phi,U)      bounded Gauss linearUpwind grad(U);
div(phi,U)      bounded Gauss upwind;
div(phi,U)      bounded Gauss limitedLinear 1;
div(phi,U)      bounded Gauss linear;

To reduce the investigated settings, I suggest the following:

• no wall functions
• residual control at 10e-5
• k-omega-SST model

Regarding the implementation, I suggest adding another Allrun file to turbulentFlatPlate_noWallFunc, possibly called Allrun.divSchemes, to test the different divergence schemes.

Best, Andre

[AndreWeiner]

Dear Jihoo,

thanks for the update on the different divergence schemes. It might be that the oscillations arise from the omega solution. I found similar results in some of the original NASA test cases for the k-omega-SST model. We'll evaluate the results in more detail during our next meeting.

Next, I would like you to test how the Spalart-Almaras (SA) model performs. The SA model is simpler (only one additional transport equation) and might be easier at the beginning for our undertaking. The following two resources will help:

• SA setup in OpenFOAM; you can copy the necessary files from here
• NASA SA test cases; from there you get the boundary condition for nuTilda

Here are the main steps to modify the setup:

• in 0.orig, you need a new nuTilda file; if the boundary conditions are unclear, reply in this issue; the inlet value you find in the second link above; at the wall, nuTilda should be zero
• in constant/turbulence properties specify SpalartAllmaras
• add entries for nuTilda in fvSchemes and fvSolution

Please, test the setup with and without wall function, and let me know if issues come up. Again, great job so far!

Best, Andre