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-   -   Can I use tabulated density data in FLUENT? (http://www.cfd-online.com/Forums/fluent/49655-can-i-use-tabulated-density-data-fluent.html)

Ellen October 29, 2008 14:06

Can I use tabulated density data in FLUENT?
 
Hi, I need to specify a temperature dependent density for a material, but the equation of d(T) is unknown, so can I use tabulated data in FLUENT? The only tabulated data I found for Fluent is the Boundary Profile, but it cannot be used for volumetric properties.

any answers would be appreciated, thank you.

Ellen

max October 30, 2008 03:53

Re: Can I use tabulated density data in FLUENT?
 
Hello Ellen,

not directly but you can use piecewise-linear to fit your tabulated date.

cheers Max

Ellen October 30, 2008 09:22

Re: Can I use tabulated density data in FLUENT?
 
thanks for your answer, Max, actually I tried curvefit my data using piecewise-polynomial in excel. it gave me perfect fit, but the regression equation doesn't seem correct. (when I fill in data that is in the same data set used for fitting, the result is way off!!) I couldn't figure out the problem.

I'll try fitting with piece-wise linear, but my data curve is kind of complicated.

max October 30, 2008 10:36

Re: Can I use tabulated density data in FLUENT?
 
Hi Ellen, i just want to make sure that fluent doesn't require a mathematical expression for piecewise linear. All you have to do is fill in all your discrete rho(T) data pairs. The more points you enter into the better will be the piecewise linear approximation of your actually polynomial density function.

cheers Max

Ellen October 30, 2008 14:26

Re: Can I use tabulated density data in FLUENT?
 
I didn't know I can directly fill in the data points! I thought I need a mathematical formula. Thank you so much!

However, what if I have a large quantity of data points, say, 200. It would be too lengthy to manually input. In that case, do I need to use UDF to read in the data table? then how would Fluent interpolate these data? do you have any experience or suggestions on that? Many thanks.

Ellen

max October 31, 2008 04:03

Re: Can I use tabulated density data in FLUENT?
 
sometimes a journal makes your life easier. in your case the journal file should look like this.:

/define/materials/change-create "your fluid" yes piecewise-linear 200 T1 rho1 T2 rho2 ...... T200 rho200 n n n n n n n n n n

where "your fluid" is the name of your working fluid and T1 rho1 .. T200 rho200 are your temperature-density data pairs. Create this .jou file with any text editor and read it into Fluent: File/Read-Journal

Max

ellen October 31, 2008 09:14

Re: Can I use tabulated density data in FLUENT?
 
I'll give it a try right now. Really appreciate your help!

Ellen


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