[Harnoor]

Hi all,

I am trying to simulate a hot rising plume inside a cylindrical domain using buoyantBoussinesqPimpleFoam. But, the plume fails to transition inside the computational domain (since my Re is not very large). I read in a NASA research paper that you need to superimpose sinusoidal perturbations (corresponding to the most unsteady mode as per stability analysis) at the inlet velocity/temperature in order to achieve faster transition. This way I can capture turbulent regime inside my computational domain.

I am a beginner in OpenFoam and request someone to please tell me in detail "How I can superimpose sinusoidal perturbations at inlet velocity/temperature".

Tnx in advance.

[Harnoor]

I basically want to get an unsteady inlet BC as follows -

U_z = U_z + A sin(omega * t)

[HenningW]

I think what you are looking for is swak4foam and more specifik the groovyBC package it includes.

If installed (do not remember if it always is included), you should insert

libs (
      "libOpenFOAM.so"
      "libsimpleSwakFunctionObjects.so"
      "libswakFunctionObjects.so"
      "libgroovyBC.so"
     );

in your system/controlDict.

In your 0/U you should set your BC (lets say its named "inlet") like:

   inlet           
   {
     type            groovyBC;
     variables (
                       "U_x=10;"
                       "U_y=10;"
                       "U_z=10;"
                       "A=20;"
                       "f=50;"
                       "omega=2*pi*f;"
        );
     valueExpression "vector(U_x, U_y, U_z+A*sin(omega*time()))";
     value           uniform (0 0 0); // As far as I remember, this has to be here, but does nothing and can be ignored
   }

Of course you have to adapt your values. I haven't tested it, due to the lack of time, but it should set you up to a good start, I think. However, let me know if it worked or if you need additional help.

Also check out the following pages on the use of swak4foam/groovyBC:

https://openfoamwiki.net/index.php/Contrib/swak4Foam
http://openfoamwiki.net/index.php/Contrib/groovyBC