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Hello everyone,

I have a model which includes 2 weirs (each defined by two rows of nodes; tangential velocity is neglected). I have placed control sections upstream and downstream of each weir, using the extreme weir nodes to define the sections.
I observe discrepancies (up to 5%) in the upstream and downstream flowrates.

My question thus is: is this observation a consequence of the way the flowrates are computed (how can I then be certain that the flowrates upstream and downstream are equal) or do I have a problem of mass conservation through the weirs?

Many thanks for your help,
Christophe.

Hello Christophe

Theoretically, mass is conserved through weirs. However:
- yes it could be a problem of control section especially if these latters are matching only boundary nodes
- you can verify the mass conservation by post-processing the result file. Most of post-processors can compute accurately flowrates through a given section
- first, be sure you are using mass conservative schemes befor going on with you verification.

I hope that this helps
with my best regards

Riadh

Hello Riadh,

Thank you for these pieces of advice.
Have a nice day,

Christophe.

PS: Just to complete the answer:
> the control sections are indeed only on boundary points,
> I am not sure Blue Kenue allows computing flow rates in an easy way (I will try with another method),
> the schemes I use are 1;5 (I believe they are mass conservative).