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Utility to initialize LES Simulation

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Old   October 14, 2013, 12:41
Default Utility to initialize LES Simulation
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Hi Foamers

I want to use my previous RANS results as an initial field for my LES simulation in an external flow problem.
As you know in the ANSYS FLUENT, there is a:
solve/initialize/ init-instantaneous-vel
text command to generate the instantaneous velocity field out of the steady-state RANS results.

is there any analogous utility (available in OpenFOAM or written by users) that generate instantaneous velocity field from the mean RANS results for external flows?

Any help regarding this matter is appriciated
Thanks in advance
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Old   October 20, 2013, 02:21
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Nima Samkhaniani
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you can create two cases: RANS and LES
then using mapField utility to map result from RANS to LES

Usage: mapFields [OPTIONS] <sourceCase>
-case <dir> specify alternate case directory, default is the cwd
-consistent source and target geometry and boundary conditions identical
-mapMethod <word>
specify the mapping method
do not execute functionObjects
-parallelSource the source is decomposed
-parallelTarget the target is decomposed
-sourceRegion <word>
specify the source region
-sourceTime <scalar|'latestTime'>
specify the source time
-subtract subtract mapped source from target
-targetRegion <word>
specify the target region
-srcDoc display source code in browser
-doc display application documentation in browser
-help print the usage
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Old   October 20, 2013, 08:50
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Thanks Nima

I know about mapField utility. since I use the same mesh for both RANS and LES, I can simply replace my last time step from RANS to 0 folder in LES without using mapField.

My problem is that RANS calculations only gave mean values but for LES we need instantaneous values (mean+fluctuations). as I told in the 1st post in ANSYS FLUENT we can add random fluctuations to our previous RANS results by
solve/initialize/ init-instantaneous-vel
then this instantaneous values (mean+fluctuations) is used as an initial guess for LES (in 0 Folder).
I know that for channel flow there is a utility called PerturbU that is written by Eugene De Villers for LES initializations.
Is there a similar utility for External Flows?
can mapField utility add random fluctuations to our entire field?
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