# y+ and velocity magnitude

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 December 10, 2008, 04:44 y+ and velocity magnitude #1 Simone Guest   Posts: n/a Hi I've a case that have a yplus value very high (y+=2000) because the flow is high Reynolds (6 x 10^8). Previously I run a simulation with Re=1.12 x 10^7, so my y+=50. My request is: with y+=2000, the velocity magnitude is sufficient defined for initial Boundary Condition for another case?? Thank a lot

 December 10, 2008, 07:40 Re: y+ and velocity magnitude #2 Julien Guest   Posts: n/a Are you asking if having your first grid point off the wall at y+=2000 ok for high Reynolds number flow? If so, it depends on the wall function boundary condition. They typically require that the first grid point be in log-law region or below. You would have to confirm that this is the case with your boundary condition and grid. The one thing you have going for you is that the log-law region gets larger with higher Reynolds number, reaching to higher y+. You have to crunch the numbers.

 December 10, 2008, 07:47 Re: y+ and velocity magnitude #3 simone b. Guest   Posts: n/a Ok, thanks, but now i'm interested only in velocity magnitude and not in friction resistance, because i need to use that velocity for inlet for another case

 December 12, 2008, 07:44 Re: y+ and velocity magnitude #4 Philipp Guest   Posts: n/a I am not sure if I can follow you. You write that you are only interested in velocity (profile?) and not in friction. The thing is that you can not have one without the other. To get the velocities right you have to ensure that the near wall flow (friction effects) is modeled adequately -> see the comment from Julien. BR, Philipp

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