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October 12, 2012, 17:24 
Shear stress in perforated pipe for horizontal wells

#1 
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Mohammed
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I am working on the wellbore (perforated pipe) for horizontal wells. I want to calculate the shear stress tau w and friction factor f from CFX.


October 13, 2012, 03:27 

#2 
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S.Bogoda
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As far as I know, it is not easy to find friction factor by CFX as when you model it you should input streamwise and transverse loss coefficients. Without knowing them you cannot model it. So better to do a simulation or get experimental data.
Pls. this is according to my knowledge and experiences. 

October 13, 2012, 05:32 

#3 
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Glenn Horrocks
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What friction factor are you looking for? There are many definitions of it.
Wall shear stress is easy to extract  is this what you mean by shear stress tau w? 

October 13, 2012, 10:28 

#4 
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Mohammed
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Hi ghorrocks.
I mean how can I calculate the shear stress inside the pipe wall due pressure drop due to wall friction and then calculate friction factor f for turbulent flow. I am using CFX kepsilon model. Regards. 

October 13, 2012, 10:31 

#5 
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Mohammed
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Hi Sakurabogoda.
How can I input streamwise and transverse loss coefficients. Regards. 

October 14, 2012, 04:13 

#6 
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Glenn Horrocks
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Getting the wall shear stress is simple, it is a variable in the results file by default. Then you just need to get an average of it at the representative point along the length, and you can get the pressure drop from that. This is all pretty standard postprocessing.
Sorry, what is stream wise and transverse loss coefficients? How are you defining these terms? 

October 15, 2012, 00:54 

#7 
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S.Bogoda
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When you do a porous or perforated design, you have to input directional losses; streamwise and transverse. Both are related to pressure drop and transverse loss can be take in terms of Streamwise coefficient. That is why I told to do simulation or experiment, to get pressure drop.
Dear Glenn, I am doubt about how to get pressure drop by CFX without knowing directional losses. I would really appreciate your advice. 

October 15, 2012, 02:52 

#8  
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Mohammed
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Quote:
Sorry how can I do to input directional losses; streamwise and trasverse by CFX? I mean where? do you have toturial about this? 

October 15, 2012, 04:20 

#9 
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S.Bogoda
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Dear Mohammed,
Refer "Flow in a Catalytic Converter" in tutorial manual. It is about a porous domain, but you can get an idea how to modify it into your model. 

October 15, 2012, 05:22 

#10 
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Glenn Horrocks
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Assuming you have a normal fluid domain (not a porous domain) then can't you simply put a series of points (or maybe a line) along the centre line of the pipe and monitor points at the periphery? Then your streamwise loss coefficient can be calculated from the pressure drop along the pipe, and the transverse loss can be calculated from the pressure drop from inside the pipe to outside?
This is just straight forward postprocessing. 

October 19, 2012, 16:58 

#11  
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Mohammed
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Quote:
How can I do it at the postprocessing without fix it at preprocessing? 

October 19, 2012, 17:06 

#12  
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Mohammed
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Quote:
When I consider my geometry (perforated pipe) as a Catalytic Converter I have some questions 1 There is domain named (Subtarte) but how can I put in my model like that. 2 How much the value of volume porosity? 3 Set streamwise loss which one I will choose? 4 Can I use the Quadratic Resistance coefficient or another one? 5 How much value use to the streamwise coefficient Multiplier? thanks 

October 20, 2012, 05:20 

#13  
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Glenn Horrocks
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Quote:


October 21, 2012, 21:16 

#14 
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S.Bogoda
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Dear Mohammed,
All parameters depend on your design. Read CFX theory guide and there it specified how to create the domain and loss model, with/without the effect of volume porosity. Other setting has to be define by you. You should have a stramwise loss due to the wall shear. 

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