 ## Fluids

• Weiqiang Liu
Subscriber

Hi all,

I tried to use DEFINE_PROPERTY macro to define fluid thermal conductivity. The thermal conductivity is the original thermal conductivity of fluid gas added by some additional term. Firstly I tried to use C_K_L(c,t) to fetch thermal conductivity of cell. Then I added some additional term to this fetched value and return it to fluent solver. Actually, I cann't really understand this idea. How can I fetch thermal conductivity before I define it. With this method, divergence will happen.

My second method is to use kinetic theory to calculate viscosity and thermal conductivity of every species. Specific heat of every species is calculated with piece wise polynomial fit. Then mass weighted average will be used to calculate mixture thermal conductivity. By doing this, fluid can iterate normally though results are not very similar to literature.

I am wondering why would this happen? is my understanding right?

best

Weiqiang

• Karthik R

What do you mean by fetching the value of thermal conductivity? C_K_L(c,t) returns the value of thermal conductivity. I'm not sure if I fully understand your question.

Thanks.

Karthik

• Weiqiang Liu
Subscriber

Hi, Karthik,

It's like the given equation of thermal conductivity in literture is (kg+additional terms). In DEFINE_PROPERTY macro, I have to fetch kg with C_K_L firstly. Then (kg+additinal terms) is returned. However, I think this does not make any sense. Becasue I can not fetch thermal conductivity before I even define it.

Therefore, I just calculate thermal conductivity of every species with kinetic theory and then calcualte mixture thermao conductivity with mass weighted average method. This is how I get kg instead of accessing directly with C_K_L.

Do you think which way is right?

Best regards

Weiqiang

• Karthik R

Yes, you are right. In the beginning, you Fluent only know the thermal conductivities of individual species. You will need to combine them someone to get an effective kg. Once you have this number, you then manipulate based on any mathematical expression and then redefine the thermal conductivity of the gas by returning C_K_L(c,t).

Thanks.

Karthik

• Weiqiang Liu
Subscriber

Hi, Karthik, 