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-   -   more than 3 piecewise polynomial (https://www.cfd-online.com/Forums/fluent/50703-more-than-3-piecewise-polynomial.html)

 sangeeta February 27, 2009 03:35

more than 3 piecewise polynomial

I want to define a property which has more than 3 ranges of temperature. In fluent, for density if we choose piecewise polynomial then we can give maximum 3 ranges.

I want to use 5 ranges. then how could i input 2 more ranges. Can anyone help me with this?

 sathees kannan February 27, 2009 05:56

Re: more than 3 piecewise polynomial

udf can do

 sangeeta March 2, 2009 02:33

Re: more than 3 piecewise polynomial

i can use UDF for other properties. but not for Specific heat(Cp). For Cp i have 5 piece wise polynomial. So, kindly let me know how to use 5 piece wise polynomial or UDF to define Cp property.

Thank you.

 sathees kannan March 2, 2009 05:32

Re: more than 3 piecewise polynomial

sorry, I have never used UDF for Cp. but, I tried something by creating User-Defined Database. There we can give UDF for Cp, but I don't have any idea about which UDF we can use. Follow the screen-shot, it may give some clue. http://home.iitk.ac.in/~sathees/ Good Luck

 sangeeta March 3, 2009 09:54

Re: more than 3 piecewise polynomial

thanks, Do u think in similar way i can write a UDF for electrical conductivity, which is going to be part of source term in UDS for my vector potential equation.

How can i add entalpy udf. as there is no listing of enthalpy in properties list.

 agg March 12, 2009 10:04

Re: In v12, use DEFINE_SPECIFIC_HEAT

See the udf.h for the prototype. Also, the enthalpy is required in the UDF. Compute the integral of Cp from T_ref to T and assign that to *h. Heat of formation is added outside the call.

 thermal energy January 13, 2014 17:12

piecewise poynomial

1 Attachment(s)
hi friends,

ı simulate melting problem inside annulor geometry. ı use paraffin (melting range 56-58oC) as a phase change material. first, ı have boussinesq approximation. and also my material properties depends on temperature like Cp (spesific heat) and k (thermal conductivity). my problem here is that,

if ı use piecewisepolynomial for k and Cp (solid value and liquid value), ı have a convergence problem (figure attached). but if ı use constant value for Cp and k, ı have no problem and it is still converging (iteration going on)

what's the reason of this. what's wrong. thanks for help

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