Learning Forum

[chuminhkhue]

Hi, everybody.
I'm doing: particles transport is modeled by a convection-diffusion equation in ansys fluent 2023R2.
- steady-state model.

- multiphase model: Eulerian.

-Primary phase material: Newtonian.

-second phase material: non-Newtonian.

I am very confused when implementing the convection-diffusion equation using UDF.

I did it using 2 methods after read section 1.3. User-Defined Scalar (UDS) Transport Equations in Ansys Fluent Theory Guide.
method 1:define UDSI by DEFINE_ADJUST and diffusion coefficient by DEFINE_DIFFUSIVITY

Method 2: implement fully equation by DEFINE DIFFUSIVITY.

I don't know what is the most accurate way to describe the equation.

I am looking forward help from experts and knowledgeable users
Thanks you so much!!!

[Rob]

What is diffusing where? Ie what are you trying to replicate as the second phase won't diffuse in the primary phase, it'll convect and be affected by turbulence. 

[chuminhkhue]

Sorry for this omission,
it is a laminar model.
I model the transport of the particles using a convection-diffusion equation due to the motion of the mixture, composed of the primary phase and the second phase.
Assume that the particles are influenced by the motion of both the primary phase and the secondary phase.
A mixture of domains contains particles.

[Rob]

Aren't the particles the second phase? If so, their motion is covered by the multiphase model. 

[chuminhkhue]

That's right. particles (platelets) defined by UDSI and move by multiple phases

[Rob]

OK. Convection will be handled by the solver. Scalar diffusivity will be more difficult as phase boundary isn't recognised in the model and you may need to account for density. 

[chuminhkhue]

Can you suggest or give me some hints on how to implement my equation in ansys fluent?

[Rob]

Do the platelets really diffuse through both phases? If they're diffusing it's a species model, or scalar. 

[chuminhkhue]

Yes, I am describing it using a scalar model.I have tried the two methods above based on User-Defined Scalar (UDS) Transport Equations in Ansys Fluent Theory Guide. but I don't know if it matches the concept of ansys fluent.