Hi Marc,

I have the following set up for a transitional flow and it works for me:

    <FUNCTION NAME="BodyForce">
      <E VAR="u" VALUE="0" />
      <E VAR="v" VALUE="0" />
      <E VAR="w" VALUE="0.5*Kinvis" />
    </FUNCTION>

    </CONDITIONS>

    <FORCING>
        <FORCE TYPE="Body">
            <BODYFORCE> BodyForce </BODYFORCE>
        </FORCE>
        <FORCE TYPE="Noise">
          <WHITENOISE> 0.005 </WHITENOISE>
          <UPDATEFREQ> 100 </UPDATEFREQ>
          <NSTEPS> 1000 </NSTEPS>
        </FORCE>
    </FORCING>

Compared to what you have, I have the NSTEPS to set the number of time steps over which forcing is applied (not sure what is the default). The value you put as White noise is (I think) variance. So putting to much does not necessarily yield the result I want.

Cheers!
Stan

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Hi All,

What is the proper way to specify a noise force and a body force at the same time?

I am new to Nektar++, and am attempting to run a simulation of turbulent channel flow using a body force to drive the bulk flow, and a noise force to generate some initial "turbulent-like" fluctuations of the velocity field.  However, when I setup the case based on the details found in the user guide (Forcing (nektar.info) ), the resulting flow field doesn't show any "noise component".  Is there some error in my settings for this case?:

<NEKTAR>

   <CONDITIONS>

      ...

     <FUNCTION NAME="BodyForce">

             <E VAR="u" VALUE="-(Re*Kinvis/H)^2/H" />

             <E VAR="v" VALUE="0" />

             <E VAR="w" VALUE="0" />

         </FUNCTION>

     </CONDITIONS>

     <FORCING>

         <FORCE TYPE="Body">

             <BODYFORCE> BodyForce </BODYFORCE>

         </FORCE>

         <FORCE TYPE="Noise">

             <WHITENOISE> 0.5 </WHITENOISE>

             <UPDATEFREQ> 10 </UPDATEFREQ>

         </FORCE>

     </FORCING>

 </NEKTAR>

Regards,

Marc Goldbach

PhD Student, Department of Mechanical Engineering

University of North Carolina at Charlotte

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