In the case of a body force, you have to create the body force inside the "forcing" flag outside "conditions", then make a function for it inside "conditions". Have you tried to put the "noise forcing" flag outside the "conditions"? I think that the place is there. If that doesn't work, I can share with you how to set the body force with a random number to trigger turbulence, that would work for your case, I guess. Anyway, check if there is an example/tutorial using the noise forcing method and check its xml file. Em qua., 18 de dez. de 2024 às 10:46, Alexander Schukmann < alexander.schukmann@protonmail.com> escreveu:

Hello Daniel,

thank you for your suggestions and sorry for the late reply. The user guide doesn't mention any additional flag to be set for the noise forcing, but I am not sure whether it is implemented for the incompressible solver. How would I look that up?

Thanks again and all the best Alex

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Daniel Garcia <ribeiro.danielg@gmail.com> schrieb am Montag, 16. Dezember 2024 um 19:10:

Hello Alexander.

I was not aware of this forcing method. However, towards triggering transition, I've successfully used the random number generator before. To do so, you would use the body force as the forcing type and then create the function based on your desired body force. Perhaps they work in a similar way. In any case, check if that "Noise" forcing type does not require another flag on the XML file or if it's implemented using your adopted solver/set up.

Cheers,

Daniel.

Em seg., 16 de dez. de 2024 às 16:35, Alexander Schukmann < alexander.schukmann@protonmail.com> escreveu:

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Hello everyone,

I would like to follow up on a post from Wed Oct 13 02:46:37 BST 2021 titled “Noise Force Specification” that was made by another user. I am using the incompressible solver in Nektar++ 5.5.0 and trying to trigger the transition of a flow between two parallel plates (2.5D case) using noise forcing. However, it seems that the forcing is not activated at all, since the velocity component along the homogeneous spatial direction is zero up to machine epsilon. Therefore, no superposed disturbance is recognizable.

I use the following lines within the CONDITIONS section of my session file: <!-- noise forcing --> <FORCING> <FORCE TYPE="Noise"> <WHITENOISE> 0.005 </WHITENOISE> <UPDATEFREQ> 10 </UPDATEFREQ> <NSTEPS> 5000 </NSTEPS> </FORCE> </FORCING>

The value for the WHITENOISE parameter was also used by Stan back then. I tried varying it, with no effect. Does anyone know whether this is this the variance or the amplitude?

Back then, the user wrote: *I tried your suggestions, but came up with the same results (a laminar flow profile without any "noise").*

However, there doesn't seem to be a reply to that. It looks like the problem still exists.

All the best, Alex

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