[smaru]

Hello Everybody,

actually I'm trying to model a fluid flow over a pipe in icem and convert it into cfx. It's my first try to do some simulation in ansys software.

I decide to do a tetra mesh in the volume and a prism layer on the walls of the pipe. I wondered how big the cells in the prism layer has to be and found out that there is a size called y plus. I understand the theory of boundaries.
I searched a long time for the calculation and I think my calculating method is right. The simulation is an exercise for university so it would be very nice if someone could confirm my method.
At first I calculate the Reynolds number of the system:
- Re (= ~1e4 => turbulent) , and the velocity v [m/s]
- lambda [1]
- tau [N/m^2]
- y [m] for y+=5
- delta= (12.64*D)/(Re)^(3/4) [m]
- y=h0 * (q^n-1)/(q-1) = h0*7.4416 with q=1.2 and n=5
- height of the wall nearest cell: h0=y/7.4416

1.:
Now I'm not sure if I can explain (especially with my english) where my problem is. So the boundary layer theory says there are 3 layers (sublayer, bufferlayer, loglayer) and for these 3 layers there are defined y+ values (0-5, 5-30, >30). Do I have to calculate different y values with the different y+ values? But in icem I can only define the 'height' (height of the first cell, so h0) and the 'height ratio' (= q, so 1.2). Am I right?

2.:
I defined here n=5, so there are 5 layers of the prism layer. How can I find out how many layers I need?

3.:
What does the size delta mean? Theoretically it's the height of the viscous layer. It's independent of y+, but depends on the Reynolds number. So does it mean, that I have to do such a big prism layer? And then in some way to calculate how many layers I need and how big is the height h0?

I'm still not sure which turbulence model I have to choose, but I think k-omega would be good for good resolution of near-wall regions. How does the choosed turbulence model effects my calculation of y+?

It would be so great to get an answer!
I really tried to find solution for my own, but now I don't think I can find it by myself.
Thanks in advance!
greets
-smaru

[smaru]

Can someone help me?