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-   -   How to create velocity profile using the previous time step ones (http://www.cfd-online.com/Forums/openfoam-solving/98511-how-create-velocity-profile-using-previous-time-step-ones.html)

 ngcw1986 March 12, 2012 23:47

How to create velocity profile using the previous time step ones

Dear all,

I am doing a large eddy simulation case, and I run into a trouble to define inlet conditions, explicitly the turbulent velocity.

The turbulent velocity has such a formation: u'(t)=u'(t-delta_t)*exp(-t/T). For u'(t) is not a direct function of time, it causes a great pain to rebuild such a inlet turbulent velocity for me.

I tried a lot using groovyBC of swak4FOAM, used to extract the previous time step value of u@inlet but failed. I wondering anyone can help me out.

Considering my poor skill using swak4FOAM and little experience with openFOAM, I hope I did not propose a stupid questions!

Thank you in advance! Great regard and best wishes!

 gschaider March 13, 2012 19:00

Quote:
 Originally Posted by ngcw1986 (Post 349050) Dear all, I am doing a large eddy simulation case, and I run into a trouble to define inlet conditions, explicitly the turbulent velocity. The turbulent velocity has such a formation: u'(t)=u'(t-delta_t)*exp(-t/T). For u'(t) is not a direct function of time, it causes a great pain to rebuild such a inlet turbulent velocity for me. I tried a lot using groovyBC of swak4FOAM, used to extract the previous time step value of u@inlet but failed. I wondering anyone can help me out. Considering my poor skill using swak4FOAM and little experience with openFOAM, I hope I did not propose a stupid questions! Thank you in advance! Great regard and best wishes!
I don't really understand what you're trying to do. Anyway. The development version (the one downloaded by mercurial) has a function has a function oldTime(U) that gives you the value of a field at the last time-step. Use with care

 ngcw1986 March 13, 2012 22:53

Quote:
 Originally Posted by gschaider (Post 349293) I don't really understand what you're trying to do. Anyway. The development version (the one downloaded by mercurial) has a function has a function oldTime(U) that gives you the value of a field at the last time-step. Use with care

Thanks for your quick reply,Bernhard. Thanks very much!

Okay, well, it's time for me to improve my English. I am sorry for my vague expressions.

What I really want to do is using the old time step value of U at inlet to construct a "new" U for the new time step at the same inlet patch. I am not quite familar with the OpenFOAM variable and swak4FOAM functions and tried and failed may times.

It is excited to hear your news! May be I can download it and try this new feature.

Great regards and best wishes!

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