[force_95]

Hey all.

I'm dealing with a dynamic mesh. I use the smoothing diffusion setting in order to let the mesh move uniformly. During the simulation the console says that there are reversed flows in my Outflows. How can I avoid this ? Or isn't it a problem ?

Best regards

[BlnPhoenix]

Originally Posted by force_95

Hey all.

I'm dealing with a dynamic mesh. I use the smoothing diffusion setting in order to let the mesh move uniformly. During the simulation the console says that there are reversed flows in my Outflows. How can I avoid this ? Or isn't it a problem ?

Best regards

Are you doing single or multiphase?
How good is overall mass conservation with reversed flow?
Generally speaking can reversed flows be avoided by extending the outlet region.

[force_95]

At the moment, I'm just simulating with water liquid.
Where can I find information about mass conservation ?

I just don't understand because when I use the spring based method, I don't get reversed flows, but the mesh is getting so thin that I get floating point exception error.

[BlnPhoenix]

Originally Posted by force_95

At the moment, I'm just simulating with water liquid.
Where can I find information about mass conservation ?

I just don't understand because when I use the spring based method, I don't get reversed flows, but the mesh is getting so thin that I get floating point exception error.

Your simulation is transient i assume. Since your dealing with single phase, reversed flow is not so problematic. You should check convergence however by calculating the mass conservation. Mass or Volume flow at inlet = mass or volume flow at outlet. So the difference in mass/volume flows diveded by mass flow at inlet should be less than 1%. The lower the better, since ideally in reality there is no mass lost in the system.

Regarding your question about spring based method i don't know what that is.
Reversed flow comes from a vortex that is present at the outlet region (hence extending the outlet region) or by a faulty BC that creates a reflux from your outlet..

[force_95]

Yes its transient.
Unfortunately I cannot change the geometry in order to extend the outlet. I have two outflows and two walls. symmetric

[BlnPhoenix]

Originally Posted by force_95

Yes its transient.
Unfortunately I cannot change the geometry in order to extend the outlet. I have two outflows and two walls. symmetric

Ok, i see. Then check the mass balance over the whole domain. Reversed flow at the outlet should not be a problem, as long as it's physical and not caused by boundary condtion itself.

[force_95]

thank you very much for your answers!

Hope I will solve the problem