Reply To: Non-reactive and non-diffusive passive scalar transport

[Ayan Paul]

Hello Rob, thank you for taking the time to answer. I have made some changes taking account of your advice and I would like to ask a few more questions because I am still unsure whether my species transport model is correct.

My simulation setup is as follows:

My setup is as follows:

(i) Pressure-Based solver; transient simulation; 3D artery geometry w/ 1 inlet and 2 outlets; Gravity disabled.

(ii) Energy off

(iii) Viscous laminar

(iv) Species transport with inlet diffusion enabled (more detail about the mixture given in the image below)

(v) Boundary conditions:

• no slip condition
• puslatile inlet velocity for blood
• pulsatile outlet pressure for blood
• a rectangular function to define inlet velocity of iodine species
• wall set to zero diffusive flux

(vi) Solution Method: Simple

My quesitons:

1.  Since the two species do not react, I have chosen the inert-mixture option. The iodine solution will diffuse into the blood (bulk species, fluid domain) and I have selected the "inlet diffusion" option.  How does choosing "inlet diffusion" will affect the simulation?
2.  I am using a simple rectangular function to define the velocity of the iodine solution at the inlet. The mass fraction of iodine is set to 0.1 at this inlet face. I set an arbitrary value of 0.2 ms-1 for the injection which last for only 1 second. Here is the UDF part of it:
   

   DEFINE_PROFILE(rectangle_velocity, thread, position)
   {
   face_t f;
   real t = CURRENT_TIME;

   begin_f_loop(f, thread)
   {
   if (t <= 1) // During injection time
   F_PROFILE(f, thread, position) = 0.2;
   else // After injection time
   F_PROFILE(f, thread, position) = 0.0;
   }
   end_f_loop(f, thread)
   }

   I am running the simulation for 32000 timesteps with 0.01 time resolution. Is the above profile correct for the iodine injection?
3. I used the Gambill method to find out the mixture density and viscosity for varying mass-fraction of each species. I set the viscosity for the for the mixture to the constant amount calculated for iodine mass fraction of 0.1. But I could not set the density to the calculated constant value and so opted for the option "volume-weighted-mixing law" because I had already defined materials properties (density & viscosity) for both iodine and blood earlier. Is this correct given my setup and is there any other way to do it such as writing the value into the UDF and then laoding it from there?

4. I am struggling to define a inlet for the iodine injection. I selected a face of the inlet to act as the inlet for the iodine solution and the rest of face as an inlet for the blood. This cannot be correct. Both species enter the fluid domain at the same inlet. Because I am defining a seperate velocity profile for iodine injection, is it possible to select a particular coordinate on the inlet face for the second species?