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Is Fluent valid for low Re condition?

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Old   January 13, 2005, 04:26
Default Is Fluent valid for low Re condition?
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I hear from someone that fluent results are quite bad for low Re fluid. Is it true?

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Old   January 13, 2005, 04:28
Default Re: Is Fluent valid for low Re condition?
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Sundar
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Not really !
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Old   January 13, 2005, 05:04
Default Re: Is Fluent valid for low Re condition?
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So how is the deviation of the fluent results? Thanks, Sundar
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Old   January 13, 2005, 05:07
Default Re: Is Fluent valid for low Re condition?
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Sundar
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Hey, Are you looking at turbulent flows ? Let me know. Would you like meet me at hotmail msn ? Sundar
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Old   January 17, 2005, 09:00
Default Re: Is Fluent valid for low Re condition?
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Not turbulent. The laminar flow is not accurate with big deviation.
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Old   January 20, 2005, 23:37
Default Re: Is Fluent valid for low Re condition?
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swarup
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Fluent is very well applicable for low Re flows. are you using very small dimensions in geometry say 40 micron or so? if so, and if you are treating a gas flow (check even if liquid flow is treated), then you should check whether Knudsen number is greater than 0.01. if so, continuum assumption may break down and deviations may be observed.
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Old   February 5, 2005, 03:25
Default Re: Is Fluent valid for low Re condition?
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How to check Knudsen Number? Yes, you are right. My computational domain is around 40*40*40 micron. It is just a simple water flow past a sphere with radius 1 micron. But I think for such a dimension the N-S equation should be applicable.
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Old   February 5, 2005, 03:28
Default Re: Is Fluent valid for low Re condition?
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Has somebody used fluent to simulate flow in channel with the dimension of tens microns?

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Old   February 6, 2005, 00:52
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swarup
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Hi i am simulating a microchannel with liquid phase reaction in single phase. However, my channel is not 10 micron width/dia. actually, continuum assumption holds for Knudesen number less than 0.01 and Knudesen number depends upon characteristic channel dimension and mean free path or an equivalent measure of intercollision distance between molecules. thus, Kn=lambda/characteristic dimension(e.g. width or dia of channel). if my guess is right, 10 micron may be too a small dimension for gas flow but may work for liquids depending upon Kn. in Nguyen's book "Fundamentals and Applications of Microfluidics", a chart explaining Kn and continuum assumption applicability is given. you may consult that. regards, swarup.
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Old   February 6, 2005, 01:03
Default Re: Is Fluent valid for low Re condition?
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swarup
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Hi, The Knudsen number is Kn=(intercollision distance or mean free path of molecules)/(characteristic channel dimension). i guess the particle is confined in a channel/cavity. you may choose the characteristic dimension according to your flow geometry. validity of NSE will depend upon Kn. regards swarup.
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Old   February 6, 2005, 07:40
Default Re: Is Fluent valid for low Re condition?
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Thanks, swarup. I have checked the mean free path of water fluid is about 3x1e-10m, and the Knudesen number is quite smaller than 0.01. I have given you an email, we can disscuss this problem.
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