# Power Law Velocity Profiled UDF

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 May 9, 2014, 22:48 Power Law Velocity Profiled UDF #1 New Member   Patrick Wayne Join Date: Nov 2013 Posts: 3 Rep Power: 5 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

 May 11, 2014, 06:43 Error Message? #2 New Member   Join Date: Mar 2014 Location: Switzerland Posts: 10 Rep Power: 5 Could you please post the error message from Star-CCM+ in order to understand what is not working. Cheers

 May 12, 2014, 12:53 #3 New Member   Patrick Wayne Join Date: Nov 2013 Posts: 3 Rep Power: 5 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

 May 12, 2014, 19:50 #4 Senior Member   Join Date: Nov 2010 Location: USA Posts: 904 Rep Power: 13 Your field function looks fine. The problem probably lies with the mesh or BCs. Does it blow up immediately or after some iteration?

 May 12, 2014, 20:10 #5 New Member   Patrick Wayne Join Date: Nov 2013 Posts: 3 Rep Power: 5 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. P.Wayne

 Tags duct flow, field functions, power law, udf, velocity profile

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