Learning Forum

[luna6362]

Hi everyone! I am using MRF approach to simulate a roatating circle plate in a simple container.

But I am wondering how the moving region larger than the plate should be? Thank you!

[Rob]

As small as possible but big enough to avoid artificially constraining the mesh into the gaps. 

[luna6362]

Hi Rob! Thank you for your response!

May I ask a question regarding the streamline breakpoints between the static domain and the moving region?

I am trying to enhance the mesh in the moving region, but there are still breakpoints present.

Is it possible to make the streamline and the color of the velocity smoother?

[Rob]

You may. If that's CFD Post check the pathlines in Fluent. CFD Post and Fluent's rotating zones don't always play well. 

[luna6362]

Thank you!🤣

Yes this is CFD-Post. So it is recommend to see the streamline in Fluent directly?

[Rob]

:) 

Yes.  We did recommend CFD Post for Fluent for a few versions but upgraded Fluent's functionality to negate the need, and only train that, as of about R19. 

[luna6362]

I just looked at the streamlines directly in Fluent, and the effect is great!

If I don't check the Relative Pathlines option, does it show me the streamlines based on absolute velocity?

How should I adjust it if I want to increase the number of streamlines?

Sorry for having so many questions. Thank you so so so much!!

[Rob]

I think so, yes, but that's generally not needed. We usually leave the default as we want to see how the flow is behaving. 

Number of streamlines is based on the release, and you'll see one stream per cell/facet. 

[luna6362]

Thank you so much!

I'm actually still not quite sure what the actual difference is between the streamlines drawn based on absolute velocity and those based on relative velocity.

If the streamlines are drawn based on absolute velocity, they represent the flow field observed from a stationary coordinate system.

If the streamlines are drawn based on relative velocity, they represent the flow field observed from a moving coordinate system. 

I'm not sure if my understanding is correct, haha. It's really difficult to fully grasp the MRF method.

[Rob]

MRF is simple once you work out what it's doing, but never gets easy to explain.