Dear CFD experts,

My question is about the capabilities of FLUENT; we are planning to model the dough like viscoelastic flow in the kneading zone of twin screw extruder (rotor-stator system with strong interaction between rotor and stator).

We already have licence of Fluent. However I read that Fluent is not good at modeling of viscoelastic flow (even with user defined function). They suggest Polyflow generally.

I know that Polyflow is much better than Fluent in viscoleastic flow modeling.

However how bad fluent is? Does it worth to buy the licence of POLYFLOW instead of spending effort in FLUENT?

In our case good match between the experimental results and simulation results is quite important (mainly data regarding viscosity).

I would be glad if any expert could help me on this problem. (price of the Polyflow really forces one to ask this question everday!

Thanks a lot

A.

Dear Ankur,

Have you compared the cost of POLYFLOW against what it will cost you to reimplement the viscoelastic model in FLUENT?

You must answer yourself a few questions. I would start with :

1 - Do you know what viscoelastic model works best for my problem/setup? That will help reduce your reimplementation cost. If you miss this one, you will have to add safety factor to reimplement another model. You are paying for this when getting POLYFLOW

2 - How familiar are you with FLUENT UDF's details?

3 - How familiar are you with the equations you plan to model?

4 - Viscoelastic models usually require transport equations for the "extra" stress. This stress is not a scalar quantity; therefore, you must model it as 6 (3D) scalar components. If the problem include any rotational periodic bouundary, you must deal with the transformations yourself within the UDF.

5 - How much verification are you willing to do before running the real case?

6 - Is the default discretization in FLUENT good enough for modeling viscoelastic flows? (5) will answer some of those questions; however, if it is not what you expect, then you need to know how to change the numerics settings in FLUENT.

Good luck selecting the appropriate tool

Opaque

Dear Opaque,

Thank you very much for your answer which is quite helpful.

I am PhD student, and actually the questions you asked are the questions that I am planning the follow and answer.

And ,as you wrote, last question is "is the default discretization in FLUENT good enough for modeling viscoelastic flow?". If the answer is "reasonably yes", I am ready and have time to start with defining best model then modeling in UDF etc.

As you appreciate it could be real waste of time, if FLUENT is not good enough to solve viscoelastic models after all this effort.

So instead of question 1, I would like to start with 6. one :"is the default discretization in FLUENT good enough for modeling viscoelastic flow?" or can it be good after changing the numerics settings in FLUENT to model Viscoealstic flows?.

I have time to follow and answer all the questions you wrote, but I dont have time to waste and I would be glad if you could help me on this problem with your expertise.

Thank you for your time and help.

a.

[saeedshayae]

Hi dear friends
I want to model a viscoelastic fluid in FLUENT, But I don't know exactly what material should I choose in the Fluent-Database to be a viscoelastic fluid. Can anyone help me on this.