## Fluids

#### Ansys Fluent Two-fluid models is a two-way coupling ?

• sekhariitkgp
Subscriber

Dear all,

We are modeling a slurry transport (liquid-solid flow) using Ansys Fluent. Our modeling approach is the Two-Fluid-Model (TFM) with closures from the Kinetic Theory of Granular Flows (KTGF). As we know, the continuous phase is liquid, and the discrete phase is solid particles. We applied the granular option to solid particles. We would like to know "TFM with closures from the Kinetic Theory of Granular Flows (KTGF) is the TWO-WAY coupling or Four-way coupling. We are confused based on Ansys's fluent theory guide. From the literature, we understand that it is a two-way coupling. But theory guide mentioned that it is a " four-way" coupling for high loads.

Can you kindly clarify our technical doubt on this? I appreciate any help you can provide.

• Rob
Ansys Employee
That's an explanation of the theory behind particle interactions. In two way coupling (DPM model) flow affects the particle trajectory, and particle drag alters the flow: there is no particle-particle interaction. In the Eulerian model we include terms for granular temperature and viscosity: ie the particles bounce and rub over each other, and that is termed "4-way coupling".
As an aside the afs.enea.it version of the documentation is likely out of date, and breaks a few copyright rules. If you click on Help in the Fluent solver (and most of the other products) you'll get to the correct version, and if you have the current version installed the latest documentation. That also includes a few tutorials.
• sekhariitkgp
Subscriber
Hello Rob Thanks for your response on this. But I wonder which term in the governing equations will consider the particle-particle interaction. Solid particles are treated as fluid in two-fluid models in a continuous medium. I am still confused about how to call it a four-way coupling. Let's assume if it is a four-way coupling, how to play/study the particle-particle interactions, which are the main parameters to consider the particle-particle interactions. I understood that particle resolved Direct Numerical Simulation will come under four-way coupling.
Important to mention that I did not find the "Four-way coupling term in the help file. I just used the search option also verified all the pages.
Once again, looking forward to hearing from you.
Best regards
Sekhar
• Rob
Ansys Employee
The term is used in the training course, I assumed we'd extended the documentation. and I wrote the course....
Eulerian uses a bunch of maths to calculate the particles as a "fluid". The granular temperature and viscosity (plus some other bits) are used to calculate the particle-particle effects. Drag and the like cover the phase interaction(s) to the carrier phase.
• sekhariitkgp
Subscriber
Hi Rob In summary, do you want to call it a Four-way coupling?
• Rob
Ansys Employee
In Eulerian, yes we do. But only when teaching, the term is rarely used as it's generally, 1-way, 2-way (both DPM) or Eulerian Granular. Remember that whilst can derive all of the equations (I can't) we're usually working with commercial users so tend to focus more on the "how to make it work" than the underlying maths: I tend to be working at the edges of what's sensible with the code.
• DrAmine
Ansys Employee
particle-particle interaction: Either you model that like using theory of dense gases (KTGF in Ansys Fluent) or you calculate it assuming Soft-Sphere or Hard-Sphere Approach (DEM is soft-sphere). DEM can be used on top of Lagrangian Particles.
When particle-particle interactions are accounted for + particles "disturb" the flow-> 4-way coupling.