Learning Forum

[Ankan Dey]

Hi,

I want to model a hollow shaft rotating at a particular speed with fluid flowing through it. Should I assign rotating speed to both shaft and the liquid? or only either one? How to incorporate the relative velocity between the shaft and the fluid? Please let me know.

Many thanks,

[Rob]

There are a couple of options. If you rotate the fluid zone the wall(s) can be set to move at zero relative speed. If you move the wall then that also works. 

[Ankan Dey]

Thank you for your reply.

I tried to rotate both, it was working. In my model the liquid has an inlet velocity and the shaft is rotating at a particular speed. So the fluid will also try to rotate at a rotational speed. But I could not figure out how to find out the relative velocity between the fluid and the shaft. Can you please suggest.

Many thanks,

[Rob]

Do you want the fluid to swirl on the way in too? Have a look in the post processing options, you may need a custom field function if "relative" isn't appropriate. 

[Ankan Dey]

Thank you for your reply.

Yes, I want the fuild to swirl on the way in. I am not sure how to do it. What kind of custom field function do I need? Could you please explain a bit more. Could you please suggest any  tutorial related to this.

Many thanks,

[Rob]

For the inlet you can set relative to cell zone, so if you rotate the cell zone the inlet ought to move at the same speed. However, that may not be what you're after. Have a look at Expressions, Profiles and/or DEFINE_PROFILE UDF. Tutorials are available via Help in Fluent. 

Custom Field Functions are a way to add in additional post processing data, so you can subtract a value from velocity (for example), they're under the User-Defined tab. Expressions are slowly replacing their functionality, but not yet for post processing. 

[Ankan Dey]

Thank you very much for your reply.

I will try to make the model, will let you know.

Many thanks,

[Ankan Dey]

Hello

I tried to implement the swirl flow model. But I do not know how to include coriolis acceleration and centripetal accelaration terms. Could you please suggest.

Many thanks,

[Rob]

For the boundary you're just adding a velocity profile based on "stuff". 

[Ankan Dey]

Sorry, I did not understand. Could you please explain. I was trying to add an acceleration term in the operating condition. But how can I add coriolis acceleration and centripetal accelaration terms? Please suggest.

Many thanks,

 

[Rob]

If you need acceleration in the flow region that's not covered by the rotating zones or gravity you may need a UDF to add momentum into the domain. I don't see why you'd need that here, but without pictures I can't comment: I also can't offer much advice beyond software use due to the rules Ansys staff work too. 

[Ankan Dey]

Thnak you very much for your comments. I will try to create a UDF.