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[ICEM] yplus calculation & transmission into icem cfd 

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May 7, 2016, 06:22 
yplus calculation & transmission into icem cfd

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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^n1)/(q1) = 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 (05, 530, >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 komega would be good for good resolution of nearwall 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 

May 9, 2016, 02:56 

#2 
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Can someone help me?


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boundary layer, calculate, wall, yplus 
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