Learning Forum

[aitor.amatriain]

I want to use an RGP table for some simulations with a single-phase fluid using the pressure-based solver. I have read the manuals,

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/cfx_mod/cfxRealRealOrga.html

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/cfx_mod/cfxRealRealSupe.html 

but there are some things that are not clear to me:

1- Do I need to provide all the values of Tables 1 to 9? The specific enthally (energy equation), the speed of sound (parameter used in the solver), and the dynamic viscosity and the thermal conductivity (parameters of the N-S equations) are definitely needed. But what about the rest of them? Are they used by Ansys Fluent in my case?

2- The same question applies to other parameters such as the critical and triple points,  and the saturation and superheat temperatures. I think that the solver does not need them for my application.

3- In Tables 1 to 9, the values of some parameters are plotted as a function of temperature and pressure. But where are the values of temperature and pressure written?

Thank you,

Aitor

 

[Federico Alzamora Previtali]

All of the tables, with the exception of dynamic viscosity and thermal conductivity are required. Dynamic viscosity and thermal conductivity can also be specified with constant values in the .rgp file header and as constants or CEL expressions in the CCL material definition. Constant values of dynamic viscosity and thermal conductivity are often acceptable in turbulent flows because turbulent diffusion normally dominates molecular diffusion processes.

[aitor.amatriain]

Thanks for the answer. I also read those sentences in the manual, but they do not answer the questions for my particular case.

[Rob]

If you're in Fluent and turn the model(s) on check what shows up in the materials panel. If it's in the panel you need to check it's correct, or understand the implications if it's not! 

[aitor.amatriain]

I have used as a reference the table shown in this page

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v231/en/cfx_mod/cfxRealRealOrga.html

and I have modified the values of the pressure, the temperature, and the properties (from tables 1 and 9) accordingly. However, I get the following error:

"No superheat/subcooling data found"

 

The table by default is read correctly without an error. However, if I modify the values (and the number of temperature and pressure points, np and nt), I get the error shown beforer

 

I do not understand what should I do. I did not modify the saturation table by default because I am not considering phase change.

 

 

[Rob]

Are you using CFX or Fluent? The manual is CFX but you mention Fluent in the OP. 

[aitor.amatriain]

I am using Fluent, but no information is given in the Fluent manual about this topic, so I took as a reference what is stated for CFX.

[Rob]

Do you cause an overlap of any sort by adjusting the values? Just wondering if the modifications mean you're defining a data value above/below one of the sat values you're not expecting to use. 

[aitor.amatriain]

I adapted the PMIN, PMAX, TMIN, and TMAX (for both superheat and saturation) values to the ones of my tables. I also modified the values of nt and np to the corresponding number of pressure and temperature points of my tables. I left unchanged the SAT TABLE, SSUPERCOOLING, P_CRITICAL, P_TRIPLE, T_CRITICAL, and T_TRIPLE, since they are not applicable to my case.

In any case, reading the table mentioned (the one available in https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v231/en/cfx_mod/cfxRealRealOrga.html) in Fluent does not give errors, but I am still not sure if this is the correct approach since there is no documentation.

 

 

[Rob]

Not sure. I'll log a documentation enhancement request; I agree it needs extending/adding.  I suspect the tables aren't commonly used so I'm also not aware of anything on the Customer Portal or Learning Hub. 

[aitor.amatriain]

Thank you!