CFD Online Discussion Forums - Including source term into energy equation

Hi all,

I am trying to include the term V.Grad[P] --> (u.dp/dx + y.dp/dy) as a source into the energy equation when solving with Eulerian Multiphase model. I am a newbie to UDFs, hence any help is well apreciated :D

So far I came up with the following (considering that once I have something working I will still need to implement it in parallel):

Code:

#include "udf.h"

#include "mem.h"

#include "sg_mphase.h"



DEFINE_SOURCE (VGradP, c, t, dS, eqn)

{

  Thread *thread_gas, *thread_liq, *superthread;

  Thread *mix_thread=THREAD_SUPER_THREAD(superthread);

  real source, x_liq_vel, x_gas_vel, y_liq_vel, y_gas_vel;

  real p_op;



  thread_liq = THREAD_SUB_THREAD(mix_thread,0);

  thread_gas = THREAD_SUB_THREAD(mix_thread,1);



  x_liq_vel = C_U(c,thread_liq);

  y_liq_vel = C_V(c,thread_liq);

  x_gas_vel = C_U(c,thread_gas);

  y_gas_vel = C_V(c,thread_gas);

  dS[eqn] = 0;



  if (NNULLP (THREAD_STORAGE(t,SV_P_G)))

  

  source = x_liq_vel*C_P_G(c,thread_liq)[0] + y_liq_vel*C_P_G(c,thread_liq)[1];

  return source;

}

The case is 2D, axi-symetric, pipe for Liquid with constant density or compressible liquid (primary phase) and compressible gas (ideal gas or another real gas model) as secondary phase.

Since I have a compressible gas, Fluent tells me to use the operating density with value = 0, so that it calculates the densities with the real Absolute Pressure, i.e. it won't subtract the column pressure g*Rho_0*h. Therefore, I need somehow to guarantee that my UDF is actually using the right pressure for the calculations.

I am not sure if I will have to work with "Data Access Macros", such as area, face, centroids, etc.

Hopefully, the code above (I know it is wrong), gives an idea of what I have in mind for the UDF.

Thank you in advance for your time,