Learning Forum

[manelaero2020]

Hi freinds ;

1/ Is back flow = reverse flow in fluent ?

Back flows occur generally in the case of a pipe flow( slope , drop in pressure gradient ...)

In the case of a flow with a minimal possibility of reverse flow occurence ( example compressible flow in a nozzle , or external supersonic flow) ; what do you think :

: Should i check " Prevent reverse flow " ? ( please see photo attached) .

Thanks you very much

Best regards

a.JPG

[Karthik Remella]

Hi,
Yes, back flow is equivalent to reversed flow (especially on the outlet boundary).
Please extend the computational domain further in the outlet direction. This might help alleviate the reversed flow issue.
This option 'Prevent Reversed Flow' should be used as the last resort.
Thanks.
Karthik

[ai0013]

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Hello,

In the case we can't extend the length of the domain, is it possible to alleviate this with another strategy? I am simulating transient pressurized coal combustion in a reactor, please see attached.

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[Karthik Remella]

Hello,
It would be useful to create a new discussion if your post is on a different problem from the one discussion in any thread.
Unfortunately, as Ansys employees, we are not able to download any attachments from the website. Please post screenshots of the problem directly in the post.
There are multiple reasons for backflow (in general). The most common one being because of a low pressure region created in the middle of the computational domain (slightly upstream of the exit). This is commonly prevalent because of flow separation and this can be avoided by extending the computational domain along the exit direction. The pressure outlet condition is not physical, if the region of separation is in close proximity to the exit.
However, in certain cases, backflow is reasonable and does not effect the overall results of your simulation (a good example might be a VoF problem involving a capillary flow). In other cases, pressure outlet is the reason for backflow and you might want to use a different boundary condition (perhaps, mass flow outlet - I'd be very careful when using this boundary condition).
This is a very general answer. Please create a new post and ask your specific question.
Thank you.
Karthik

[phanicmsf]

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Thank you Kremella .

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