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-   -   laminar pipe flow? Fluent gives wrong result (http://www.cfd-online.com/Forums/fluent/34998-laminar-pipe-flow-fluent-gives-wrong-result.html)

SAM November 4, 2004 19:44

laminar pipe flow? Fluent gives wrong result
 
hi

i am simulating cornel tutorial on laminar pipe flow.

i am using same boudnary condtions i.e

d=0.2 m length = 8 m velocity inelt= 1 m/s pressure outlet = 1 atmospheric density = 1 m3/kg viscosity = 2e-03 Reynolds number = 200

From books using formula for laminar pipe flow my answer is 12.8 for pressure drop and from cfd it is 3.1 wat is wrong


Philipp Beierer November 5, 2004 02:23

Re: laminar pipe flow? Fluent gives wrong result
 
Could it be that the solution of your book assumes a fully developed flow at the domain inlet? In case you use the figures as stated above for your CFD model, the flow is not developed at the inlet (check e.g. velocity vectors at the inlet). Now you can either add some extra pipe to your inlet in order to achieve a fully developed pipe flow in the range of interest, or you use a udf to define a velocity profile at the inlet that represents the fully developed flow.

Good luck!

SAM November 5, 2004 02:39

Re: laminar pipe flow? Fluent gives wrong result
 
problme solved

i have to multiply by 16/Re, but i dont know why in book other problme are solved by withouth mulitplying pressure drop by friction factor(16/Re).

yes this flow is fully developed as teh velocity is not changing axially

regards


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