Learning Forum

[sraykar8]

I am using ANSYS Fluent to do a transient heat conduction simulation. The material property-specific heat for one of the materials is complicated and to capture the behavior I am using a series of order 5 or 6 polynomials. 

A typical polynomial equation looks like shown below:

Cp=-111.901539044454*(T^5) + 160732.871948007*(T^4) - 92348942.2355927*(T^3) + 26529419205.7051*(T^2) - 3810589467578.09*(T) + 21893499260717.

But when I add these equations into ANSYS Fluent through the material properties as a piecewise polynomial Fluent rounds off the coefficients and this introduces an error in the specific heat that it calculates. I also tried using a UDF to do the same and based on the results I think even in that case Fluent rounds off the coefficients. 

For obtaining the correct specific heat values I need Fluent to not round off the coefficients, is there a way to do this? 

Or is there something else that I can try? 

[Rob]

If you're using coefficients that are that many significant figures then you're going to have problems, and I'd be surprised if the curve calculation was that precise too. What does the original data curve look like? 

[sraykar8]

Thank you for your reply.

I can send the excel file for your reference. If you need it please let me know. 

I am attaching a screenshot of the curve.

 

One of the suggestions I received was to use a lower order polynomial. So I plan on using more polynomials with the maximum power I will use is 2. Do you think this work? 

 

Also,  when I typed in these coefficients into the material properties tab Fluent displayed rounded off numbers. Does it use those rounded off numbers in the calculations or does it use the original numbers? If you answer this it will help me decide how to break up the polynomial. Additionally, I might have more than polynomials and thus might have to use UDFs, in that case as well will it use the original number or the rounded off number?

 

Thanks!