[jnanabrao]

Dear Foamers,
I need to implement a very specific velocity boundary condition for my LES simulation. The velocity should be decomposed into a mean velocity obtained from a RANS simulation and velocity fluctuations that are calculated as a Fourier sum. The velocity fluctuations should be as described by Smirnov(2001) This boundary condition is different to the boxTurb method implemented in OpenFOAM, in that, in Smirnov's method an orthogonal transformation and scaling of the Fourier amplitudes is performed based on the Reynold's stress calculated from a previous RANS simulation. Can anyone guide me as to where I could find such an implementation in OpenFOAM or which boundary condition could be a good starting point for developing something like this?


Ideally, I would like to code a boundary condition that generates the normalized random wavenumbers, frequencies and amplitudes as described in the paper and stores them at the start of the simulation. Then at each time step it simply uses the Fourier expansion to return the velocity fluctuations at a patch location based on the value of time and position. The final velocity would then add the velocity fluctuations and mean velocity and set that to the 'U' value at the patch.


I can code this in python but I have very limited understanding of the OpenFOAM speicific data types to write the code efficiently. I can't even figure out which existing boundary condition would be a good starting point. I'm currently working with OF-6 but any boundary condition in any release that might get me started would be helpful.


Regards,
JBR

[mAlletto]

The digital filter method of Castro and a divergence free synthetic eddy method is available in openfoam.com. you may start to look at this implementation

[jnanabrao]

Thanks...that is quite helpful.

[jnanabrao]

I was able to compile the boundary condition as I required. However, when trying to access the Reynold's stress tensor R in the 0 folder, for calculations within my boundary condition object, I get the error that no such object exists in the objectRegistry. On reading about objectRegistry class of OpenFOAM, I understood that this is perfectly sensible as the objectRegistry is usually populated by the solver and the solver doesn't require the R field when it is trying to read/calculate U, so it is not present in the registry. Is there a method to read a field, that has been manually copied to the cases directory, by a private function of my custom boundary function class?



P.S: The interpolateorRead() method used by the digitalFilterInlet boundary condition class doesn't work for me. It provides an undefined symbol error that i couldn't understand.