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Power Law Velocity Profiled UDF

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Old   May 9, 2014, 22:48
Default Power Law Velocity Profiled UDF
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Patrick Wayne
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Hello,

I'm going crazy trying to figure out how to program a 1/7th power law velocity profile (FD) for my inlet on simple duct flow in Star-CCM+. I have very little experience in programming in general and even less experience in field functions, so I really don't know what to do. I tried going off of something in the "Help" section:

[(($$Position[1] <= 0.0025) ?
1.0752*1.143*pow(($$Position[1]/0.0025),0.143) :
1.0752*1.143*pow(((0.005-$$Position[1])/0.0025),0.143)), 0, 0]

Basically, it's u(y) = u_bar*(y/delta)^(1/7) for y <= 0.0025 m. and u(y) = u_bar*((h-y)/delta)^(1/7) for y > 0.0025 m. I know this is wrong because my simulation won't run with this. Can anyone help me?

Thanks,
P. Wayne

p.s. The entire height of the duct is only 5 mm.....just in case you were wondering

Last edited by pwayne; May 9, 2014 at 22:54. Reason: Forgot Something
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Old   May 11, 2014, 06:43
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Could you please post the error message from Star-CCM+ in order to understand what is not working.

Cheers
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Old   May 12, 2014, 12:53
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Patrick Wayne
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I'll upload that as soon as possible. What I remember is that it says a floating point error has occured in regards to the segregated flow solver. Maybe that helps?

P.Wayne
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Old   May 12, 2014, 19:50
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Your field function looks fine. The problem probably lies with the mesh or BCs.
Does it blow up immediately or after some iteration?
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Old   May 12, 2014, 20:10
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It blows up just after the first iteration. It's a relief to know the function is fine though, so thank you. I'll work on the Mesh, BCs, then we'll see what happens. I didn't gfet a chance to work on it today, but I'll dive into it tomorrow.

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