LES about BC cyclic and turbulence
 

I'm ready to use LES to simulation a duct square turbulence in OF,inlet and outlet are cyclic , but there's something about BC cyclic and turbulence bother me .

Question 1：cyclic BC.
I manually set a cyclic BC wiyhout use any utility, but I saw the OF2.1/channelFoam/0.org/U ,the inlet and the outlet are divided into half,it's like inlet_half0、inlet_half1 and outlet_half0、outlet_half1 ,antbody could tell me ,why does it need divided into half,should I use any utility like createPatch or something to set cyclic ??How could I do that ?

Question 2:turbulence

Some page told me use the utility perturbU to create turbulence ,I compiled it correctly ,and use it in OF2.1.1，there are two questions I'm not clear
1.I used perturbU ,and it just created a new "U",but I saw the channelFoam,it created a new "0"folder ,the "k" "nusgs" "p" "U" became a new one ,original "0" became "0.org".why I use perturbU ,it just created a new "U" without a new "k" "nusgs" "p" ???
2.the "U" file just change the streamdirection value ,but in the channelFoam/0/U,all direction value changed ,why ??
or I should use other utility to create turbulence ??

anybody help me ?
best wishes .

anybody help me ??

Anybody knew that ??
I have the same problems

1) It is divided into 2 parts to get a concentration of points near the wall to resolve the gradients. For postprocessing the channel flow, you usually only plot one half.

It is possible to use only one block, but then you have to modify your blockMesh function to get a concentration in both directions. You can search the forum here, one user posted this function.

Nevertheless I would recommend you to keep the double parts because you can easily use the postChannel utility afterwards, that uses the symmetry.

2) the perturbU utility is to create a turbulent initial solution because it takes ages to get a proper initial solution from u=(0,0,0) or whatever.
The perturbU utiltiy was created by Eugene de Villers in his PhD thesis. You can find it on google and in several threads in this forum.

However, this utility may just be suitable for initial solution. In my simulations of the LES channel flow, I dont really trust it and I create my initial solutions from the values of the tutorial file and then simulate for a long time period with medium high Courant number.
After that, I decrease the maxCo to 0.3 or something and start averaging.

Decide yourselve if you like the perturbU utility or not. The thesis might be helpful for your decision.

I agree with Hans in Q1, while for Q2, perturbU can still be a good tool to generate your initial field, although I found that it just create almost the same field no matter what's the Reynolds number is:( If you don't have experiment data of the inlet ,perturbU is a good choice.

Hi, my friend,could I ask some questions about my simulation ,when you used the utility perturbU ,the streamwise velocity changed or all the direction velocity changed ??? The files "k""nusgs"also changed ???
I saw you are a ACU student ,I'm a Chinese student too ,could I contact you with E-mail or QQ ??thank you very much

only the velocity is changed,if you look into perturbU.C, you'll find that both the streamwise and spanwise velocity components are changed. My qq is 601369952, but I only keep online when I'm free.

OK,I'll just contact you use QQ-mail,you can answer me when you free .
best wishes

I'm sorry for a litter later reply .
Need I use the utility createPatch to create the cyclic BC?