# Paper for boundary condition of turbulence intensity at inlet

 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 21, 2022, 11:32 #21 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,064 Rep Power: 60 Did you think that you need to take the average velocity over the cross section or something? At every boundary face, you need to take the local velocity and apply the formula. You are mapping a non-uniform velocity field, which means the velocity at every face is different. The velocity is not uniform and the k field is therefore not uniform. Your issue is you don't know how to calculate k correctly and provide that list in the values, and so you plot the wrong things and it changes. The list of k at any iteration that isn't 0 is calculated correctly by OpenFOAM, which is your answer sheet to this problem! Whatever you do, you need to calculate k such that you get the same answer as the answer sheet. As soon as you calculate k correctly and put that list into the k file in the 0 directory, the k won't change anymore because it will be correct. FluidKo likes this.

June 26, 2022, 22:33
#22
Senior Member

Sangho Ko
Join Date: Oct 2021
Location: South Korea
Posts: 126
Rep Power: 3
Quote:
 Originally Posted by LuckyTran Did you think that you need to take the average velocity over the cross section or something? At every boundary face, you need to take the local velocity and apply the formula. You are mapping a non-uniform velocity field, which means the velocity at every face is different. The velocity is not uniform and the k field is therefore not uniform. Your issue is you don't know how to calculate k correctly and provide that list in the values, and so you plot the wrong things and it changes. The list of k at any iteration that isn't 0 is calculated correctly by OpenFOAM, which is your answer sheet to this problem! Whatever you do, you need to calculate k such that you get the same answer as the answer sheet. As soon as you calculate k correctly and put that list into the k file in the 0 directory, the k won't change anymore because it will be correct.
Oh I got it.
I've just slightly confused because of my bad english level.
I'm going to calculate k for inlet boundary(control surface of mesh)
by using formula and mapped velocity(uploade value).
Then I'm going to map this calculated k into 0 directiry.
After doing this I'm going to let you know ours following.
Attached Images
 Mapped velocity.jpg (65.2 KB, 0 views)

 June 27, 2022, 00:29 #23 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,064 Rep Power: 60 Keep in mind you have to get the turbulence intensity from the previous simulation also. You need to calculate k from the mapped velocity and mapped turbulence intensity. And similarly for epsilon. Btw this is purely for academic purposes and a learning exercise. As a best practice I still recommend you take map the k and epsilon fields from the previous simulation (just like you have mapped velocity). Because it doesn't just stop at velocity and turbulence; for any arbitrary number of transport models you might one day employ, you need to map everything over. For example... temperature and pressure... FluidKo likes this.

 Tags boundary condition, inlet, turbulence intensity