[s&m]

Hi to everyone!
I would like to create a turbulent initial condition for my channel flow simulation.. but i don't know how to do it! I used foamCalc randomise 0.2 U for creating a perturbation inside the velocity field.. but after few time-steps (10= 1 sec), the flow became laminar again.. So i try to perturb the flow every 10 time step.. but now i'm at 20 sec and if i don't perturb the flow, it returns laminar again (after 30 time steps= 3 second)... what i have to do?
thx

[alberto]

You probably want perturbU for the channel...

http://www.cfd-online.com/Forums/ope...-perturbu.html

[Tarak]

Hii Alberto,

Can you please let me know the best way to get an initial perturbed field for starting a LES simulation? Just like perturbU, which is for channel flow, I need to know a generalized way to get the preturbations. Presently I am using the turbulentinlet boundary condition, with 2% fluctuation. Is it a good way to generate instabilities?

Thanks,
Tarak

[alberto]

Originally Posted by Tarak

Hii Alberto,

Can you please let me know the best way to get an initial perturbed field for starting a LES simulation? Just like perturbU, which is for channel flow, I need to know a generalized way to get the preturbations. Presently I am using the turbulentinlet boundary condition, with 2% fluctuation. Is it a good way to generate instabilities?

No, turbulentInlet basically adds noise, so it's not really a good way to initialise turbulence.

The initialisation depends on the case you are considering. If you have an inlet, and have detailed information on the flow conditions there, you might want to consider synthetic turbulence BC's (you'll have to implement them). If you are interested, you should check the literature on the topic. Some OF users were working on that too, so the Turbulence SIG (see wiki) might be of help.

Best,