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Calculate k and epsilon for a turbulent multphase simulartion

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Old   February 4, 2018, 13:10
Default Calculate k and epsilon for a turbulent multphase simulartion
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Kai
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Hey Guys,
im very new in CFD and have some problems too calculate k and epsilon for my simulation.
I would like to simulate a sewershaft, with a multiphase run. I use SimScale witch based on OpenFoam. For the first run i use laminar flow, now i like to use a k-epsilon turbulance simulation.
The inlet diameter is 0,3m and der velocity is 4m/s in the y direction.
With this values i got a Re Number of 1.290.000, is it a little bit high? Sorry i dont have much experince with Re numbers.

In an older thread i found this Wikisite https://www.cfd-online.com/Wiki/Turb...ary_conditions ,but the formular dosent help me much further.

The calculation for k is k= (3/2)*(UI)^2
I think U is 4m/s, I is the turbulence intensity, the formular is I=u'/U with u'=sqrt(1/3(u'+u'+u')), in my case is u' also 4m/s? I really dont know.

This is only my first question, i would really lucky if you help me .

Thank you
Kai
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Old   February 20, 2018, 23:29
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Chen Sihe
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Hi Kai, I am also quite new here. Sry I don't have much experience for the k epsilon model, but I think your Reynolds Number is not right. For your case you may actually expect a much smaller one.
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Old   February 21, 2018, 13:57
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Kai
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Hey cshsgy,
thank you for your answer. I have used this Formular with this Numbers.

(4,0 m/s * 0,3 m ) / 0,000000933 m/s

= 1,29e+6

i use water in my simulation.

Is my calculation incorrect ?

Greetz Kai
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Old   August 5, 2019, 05:19
Default Re in pipes
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Chris
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Hey there,

For the Re you got the formula but please bear in mind that you should consider the geometry you have. With that being said the range for the pipe flow to be Turbulent is Re>2900 which is the case for you. It is completely to get such Re especially when you assume your fluid is water. This results in a Xe-6 for kinematic viscosity and hence the high values of Re.

But I did not get the full picture of your problem.
Usually, there is a way you should ask your questions in such forums to get an answer. A tip would be to include a complete description of your simulation when you open the thread. By doing so, you will save time for everyone and can get a proper (and sometimes professional) answer.
All in all, do not lose hope if you do not get anything, just do your research before asking so that you have an in-depth issue.

Regards,

Chris
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