Learning Forum

[Abhiram P]

I'm trying to write an UDF for the variaton of specific heat along the length of the micro-combustor.
I already wrote two UDFs to vary the thermal_conductivity and density along the length of micro-combustor and they worked well. I was even able to extract the graphs for them. The macro I used to write the the thermal_conductivity and density UDFs is DEFINE_PROPERTY. That is not working for the specific_heat. Later I tried another macro to vary the specific_heat that is DEFINE_SPECIFIC_HEAT. But this macro only takes T as input arguments not the cell and thread as the input arguments.


DEFINE_PROPERTY(specific_heat,c,t)
{
   real x[ND_ND];
   real cp;
   C_CENTROID(x,c,t);
   cp=a*x[0]+e;
   return cp;
}


DEFINE_SPECIFIC_HEAT(user_cp,c,t)
{
   real x[ND_ND];
   real cp;
   C_CENTROID(x,c,t);
   cp=a*x[0]+e;
   return cp;
}

These are the codes I tried to vary the specific heat along the length of the micro-combustor but they didn't work well.
Can you help me with this

[Rob]

Given the properties are functions of mixture composition and temperature why would you alter the values with position? 

[Abhiram P]

We are doing a project in which we are working on simulations of functionally graded materials being used in micro-combustors.
In that we are varying the thermal conductivity, density and specific heat along the length of the micro combustor. No one has tried this as of now, so we are trying to vary this.
As of now we succeded in writing the UDFs for thermal conductivity and density but coming to specific heat we are facing issue.
We are not varying the properties with temperature at all, we are only varying them with respect to position.

[Rob]

Yes, which I'm trying to understand. If you set the property with position aren't you assuming a result of the combustion process rather than modelling it? 

[Abhiram P]

We are not presuming these variations as outcomes of the combustion process; rather, we are modeling the micro-combustor. Our objective is to employ a functionally graded material, characterized by properties that systematically vary with position.

[Rob]

https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v241/en/flu_udf/flu_udf_ModelSpecificDEFINE.html%23flu_udf_sec_define_sp_heat   You might be able to mess with the species to do something, but otherwise it's not possible.