[Piotr95]

Hi guys,
I have a question. I'm trying to implement UDF for air flow with condensation. I use two additional governing equations for liquid water mass fraction and number of droplets. I define everything in DEFINE_ADJUST functions and then add two sources of water mass and number of droplets as DEFINE_SOURCE. So far everything works fine.

Due to the condensation there is a pressure jump in the flow. Having mass of liquid water and number of droplets it is possible to calculate the pressure and enthalpy change. Here is my question. If i correct the pressure and enthalpy as :
C_H(c, t) = h_cor; /* prescribing value of enthalpy */
C_P(c, t) = p_cor; /* prescribing value of pressure */
the solves crashes. Do you have any ideas how to introduce the pressure and enthalpy change?

Is there maybe a function like DEFINE_TURBULENT_VISCOSITY for enthalpy or pressure that is not mentioned in User's Manual?? Or maybe is there a way to change the definition of enthalpy?

[TimW]

Hello Piotr,

which problem are you researching?

Regarding your question:
I had the very same problem (condensation sources) a few months ago. From my experience, it hardly works to adjust cell values with a code like that: C_H(c, t) = h_cor;

Instead you need to use proper source terms in the continuity and energy equations. The UDFs name is DEFINE_SOURCE.

Regards,
Tim

[Piotr95]

Hi Tim,
thank you for your replay.

I solved the problem in another way. Indeed adjusting properties in cells like C_H(c, t) = h_cor makes the solver very unstable. I used the UDRGM instead, where the Cp correction is introduced.

Regards
Piotr