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A note for CFD developers and the Spalart-Allmaras model

Posted June 12, 2021 at 13:06 by sbaffini (NuTBox)
Updated June 15, 2021 at 07:00 by sbaffini

This is a pretty specific issue which relates to my experience working on wall functions and the Spalart-Allmaras model, but might be useful to others or, more importantly, the users of their code.

If you followed my previous posts here, you know I developed a wall function formulation based on the Musker wall function which, thanks to a math trick, is integrable also for arbitrary Pr/Pr_t (Sc/Sc_t) numbers and also for some forms of non equilibrium terms.

One of the...
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Connecting Fortran with VTK - the MPI way

Posted May 24, 2019 at 12:12 by sbaffini (NuTBox)

I wrote a little couple of programs, respectively in Fortran and C++, as a proof of concept for connecting a Fortran program to a sort of visualization server based on VTK. The nice thing is that it uses MPI for the connection, so on the Fortran side nothing new and scary.

The code (you can find it at https://github.com/plampite/vtkForMPI) and the idea strongly predate a similar example in Using Advanced MPI by W. Gropp et al., but makes it more concrete by adding actual visualization...
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A generalized thermal/dynamic wall function: Part 4

Posted February 7, 2019 at 10:29 by sbaffini (NuTBox)

In previous posts of this series I presented an elaboration of the Musker-Monkewitz analytical wall function that allowed extensions to non equilibrium cases and to thermal (scalar) cases with, in theory, arbitrary Pr/Pr_t (Sc/Sc_t) ratios.

In the meanwhile, I worked on a rationalization and generalization of the framework, derivation of averaged production term for the TKE equation, etc.

While the new material is presented in a substantially different manner and will...
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File Type: txt comparewf.txt (2.0 KB, 382 views)
File Type: txt musker.txt (930 Bytes, 392 views)
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A generalized thermal/dynamic wall function: Part 3

Posted October 17, 2016 at 11:25 by sbaffini (NuTBox)
Updated November 18, 2018 at 05:57 by sbaffini

In this post i summarize the initial problem and the procedure to determine the wall function value (i.e., the solution) for given y^+,F_T^+,Pr and Pr_t.

We looked for a solution T^+\left(y^+,F_T^+,Pr,Pr_t\right) to the problem:

\frac{dT^+}{dy^+}=\frac{Pr\left(1+F_T^+y^+\right)}{\left[1+\left(\frac{Pr}{Pr_t}\right)\left(\frac{\mu_t}{\mu}\right)\right]}

with:

\frac{\mu_t}{\mu}=\frac{\left(ky^+\right)^3}{\left(ky^+\right)^2+\left(ka_0\right)^3-\left(ka_0\right)^2}...
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A generalized thermal/dynamic wall function: Part 2

Posted October 17, 2016 at 08:24 by sbaffini (NuTBox)
Updated December 21, 2016 at 09:07 by sbaffini

In the first part of this post we left with the problem of computing the following integral:

f^+\left(y^+,\frac{Pr}{Pr_t}\right)=\int_0^{y+}{\frac{1}{\left[1+\left(\frac{Pr}{Pr_t}\right)\left(\frac{\mu_t}{\mu}\right)\right]}dz^+}

with:

\frac{\mu_t}{\mu}\left(y^+,a,k\right)=\frac{\left(ky^+\right)^3}{\left(ky^+\right)^2+\left(ka\right)^3-\left(ka\right)^2}

I added all the explicit functional dependencies here because we know f^+\left(y^+,1\right)...
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