Learning Forum

[abdullahhassan]

Hello, 

I am doing a Multiphase VOF simulation that includes condensation of ammonia from vapor to liquid in shell and tube heat exchanger. 

I have read a number of papers that says that VOF multiphase can only be done with structured meshing but then I studied on online platforms that Fluent - polyhedra type can be used to simulate VOF model. 

As per my knowledge, fluent polyhedra is unstructured meshes. 

Can you guide me on above confusion?

[abdullahhassan]

Dear Team, 

Kindly guide me in this matter. Looking forward for your reply. 

Thankyou. 

[Rob]

Not sure where you've read that you must use a structured mesh for VOF, we've been using tets for decades and poly cells since they came into Fluent 5+ years ago. 

[abdullahhassan]

Is hybrid mesh more reasonable then polyhedra cells?

If yes, can we make hybrid mesh with multizone methods?

[Rob]

Yes, hybrid is also fine. With the meshing changes in 2024R1 it's a toss up between poly and multizone. Note, you need to resolve the free surface so VOF for the initial condensation or bubble formation may require a significantly larger mesh than you're able to solve. 

[abdullahhassan]

I am currently using ANSYS 2023R1 version. But i am not acheiving a hybrid mesh with multizone. maybe due to lack of my expertise in fluent meshing. 

Do you mean that 2024R1 is better version for a hybrid mesh ?

 

[abdullahhassan]

Hello Rob, 

one more thing related to meshing i have in my mind, if i want to do mesh independence study of my geometry and my purpose is to perform VOF simulation. 

Can i perform mesh independence using simple transient k-e model without VOF and then after getting good mesh, do a VOF simulation on that mesh?

Is this feasible? 

or i need to perform mesh independence using VOF model. ?

[Rob]

You'll need 2024R1 for multizone. I can't remember which version it was released in but know they've added a lot of options, and expect more features in R2 and 2025Rx. 

Mesh independence would need VOF too as it's a free surface model and refining the free surface will have an impact on the solution. You'll also find the time step needs checking as you refine the mesh. 

Please also refer to my comment about the likely mesh costs of VOF. You may want to review the alternatives.