# Is Fluent valid for low Re condition?

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 January 13, 2005, 04:26 Is Fluent valid for low Re condition? #1 REACTION Guest   Posts: n/a I hear from someone that fluent results are quite bad for low Re fluid. Is it true? Thanks for all replies!

 January 13, 2005, 04:28 Re: Is Fluent valid for low Re condition? #2 Sundar Guest   Posts: n/a Not really !

 January 13, 2005, 05:04 Re: Is Fluent valid for low Re condition? #3 REACTION Guest   Posts: n/a So how is the deviation of the fluent results? Thanks, Sundar

 January 13, 2005, 05:07 Re: Is Fluent valid for low Re condition? #4 Sundar Guest   Posts: n/a Hey, Are you looking at turbulent flows ? Let me know. Would you like meet me at hotmail msn ? Sundar

 January 17, 2005, 09:00 Re: Is Fluent valid for low Re condition? #5 REACTION Guest   Posts: n/a Not turbulent. The laminar flow is not accurate with big deviation.

 January 20, 2005, 23:37 Re: Is Fluent valid for low Re condition? #6 swarup Guest   Posts: n/a 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.

 February 5, 2005, 03:25 Re: Is Fluent valid for low Re condition? #7 REACTION Guest   Posts: n/a 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.

 February 5, 2005, 03:28 Re: Is Fluent valid for low Re condition? #8 REACTION Guest   Posts: n/a Has somebody used fluent to simulate flow in channel with the dimension of tens microns? Thanks for reply!

 February 6, 2005, 00:52 Re: Is Fluent valid for low Re condition? #9 swarup Guest   Posts: n/a 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.

 February 6, 2005, 01:03 Re: Is Fluent valid for low Re condition? #10 swarup Guest   Posts: n/a 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.

 February 6, 2005, 07:40 Re: Is Fluent valid for low Re condition? #11 REACTION Guest   Posts: n/a 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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