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December 12, 2012, 06:13 
why low reynolds number?

#1 
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Hey,
I simulate a water stream through a pipe with 20mm bore. I chose the realizable ke Model and enabled enhancedwall treatment. In boundary conditions I chose the ke model with k=e=1 as turbulence specification. The incomming flow rate is 2 m/s. I calculated that there must be a turbulent flow with a flow rate of 0,0755m/s so that 2 m/s should bring reynolds numbers over 2300. But the reynoldsnumbers are maximal about 800. Maybe you can help me and tell me what I do wrong. Thank you=) 

December 12, 2012, 07:11 

#3 
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The reynolds numbers in the whole pipe


December 12, 2012, 07:19 

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I see them when I go to Results>Graphics and Animations>Contours and then Counters of Velocity> cell Reynolds Number


December 14, 2012, 00:12 

#7  
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Lucky Tran
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Quote:
It is not quite Peclet number but similar. Quote:
This is a local Reynolds number. It uses the local cell velocity, length scale and properties. The length scale is the cube root of the volume of the cell. 

December 14, 2012, 04:27 

#8  
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Quote:
Thanks It was a long time when I read them in CFD course. Thanks again. 

December 14, 2012, 06:02 

#9 
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Thank you both for your help=)
Lucky Train, can you tell me what I have to do to see the "real" reynolds number so that I can see if the flow is laminar or turbulent? 

December 14, 2012, 06:11 

#11 
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but I haven't specified the reynoldsnumber because that is my variable. I want to see how the reynoldsnumber changes when I have a different geometry.


December 14, 2012, 07:02 

#13 
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Philipp
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Re = density * velocity * length / viscosity.
Density and viscosity are material properties. Take them from the material you chose. Velocity is what you set as inlet velocity of your pipe. "Lenght" is a typical length scale of your domain. For pipes one usually takes the diameter of the pipe. Now calculate. What people here were trying to explain: Fluent can't tell you "the Reynold's number" because there is no single Reynold's number. It allways depends on the lengthscale you choose. You could also take the radius for a pipe. It's more or less arbitrary what you take...
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December 18, 2012, 06:44 

#14 
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Thank you all for your help!
I found the solution: When you look on the turbulent reynolds number Re_y it is already turbulent with a value about 200. So my flow is turbulent=) 

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