Learning Forum

[desouzadacosta]

Hi All,

We dont know a priori if a flow is laminar or turbulent. Lets suppose we did not build any physical world prototype to see the behavior. 

What are the implications for the code convergence numerical results of doing :

turbulent case (physical world) -> simulated as laminar

laminar case (physical world) -> simulated as turbulent (any RANS - steady state)

Any reflection/comment of the ANSYS experts is very welcome,

to all of us.

[mli]

In general, you will get incorrect results.

In reality you should be able to find some literature to help you determine if the flow is laminar or turbulent or in between.

[Karthik R]

Hello,

In general, it is always a good modeling practice to have the knowledge of your flow before you go to the modeling tool. It is always advisable to do some back-of-the-envelop calculations to categorize your flow. In addition to this, it is also important to develop a hypothesis of what your results would look like before running your model. I do not mean the exact values, but I think it is an important modeling step to conceptualize your physical model, before developing your mathematical model.

To answer your question about the flow:

You will not be able to run a fully turbulent flow using a laminar flow model assumption. The results, if the model ever converges (which I do not think it would), are going to be absurd.

Regarding running a laminar flow using the RANS approach - you are unnecessarily using your computational resources. You are adding two additional equations to your model, which might cause huge problems with convergence.

It is always a best practice characterize your flow and write out your model assumptions before actually modeling.

I hope this helps.

Best Regards,

Karthik