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specifying turbulance from laminar

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Old   February 12, 2007, 06:48
Default specifying turbulance from laminar
  #1
asghari
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Hi all;

How can we distinguish between turbulance from laminar flows in CFD commercial softwares or another codes?

suppose in my case ,in the biginning, my code converges,then i increase the velocity in inlet as much as fluid place in the turbulent flows,if i use no turbulance model what event is possible to happend?

Thanks in advance for everybody help me.

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Old   February 12, 2007, 09:13
Default Re: specifying turbulance from laminar
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john deas
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It might have problems to converge, or, you might have results different from the experience, because one term of the equation which is negleted in laminar flow will be completely missing.

You won't be using the equations that describe your physical system.
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Old   February 13, 2007, 09:39
Default Re: specifying turbulance from laminar
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Asghari
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Thank you,

But you suppose a case where Reynolds number=500(Low Reynolds), how can i discover that it is turbulent or laminar? I usually solve it in laminar flow , whereas flow may be turbulent.

Thanks in advance for any help.
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Old   February 13, 2007, 14:08
Default Re: specifying turbulance from laminar
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John Deas
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You can make both calculation for one general case, and look at the turbulent energy for the turbulent case. Then you can extrapolate your results to similar geometries.
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Old   February 14, 2007, 03:32
Default Re: specifying turbulance from laminar
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asghari
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Ok,but I can't still underestand how can i specify that a sample case is laminar or turbulent flow. can you present for me a detailed discussion for this object. you tell me in previous message "You can make both calculation for one general case, and look at the turbulent energy for the turbulent case" , but you did'nt indicate to turbulent criterion .For example , suppose i compute a flow using laminar model , whereas flow might be turbulent , How is this capable of distinguish
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Old   February 14, 2007, 04:17
Default Re: specifying turbulance from laminar
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john deas
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For example, you can compare in your sample zone with obstacles and zones without obstacles. If in the obstacle zone you have significatly more turbulent energy, you can deduce that using a laminar model will cost you a lot of information in this zone. As for a quantitative criterion for this... Well I have none (I am a newly introduced to CFD )
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