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hello everyone,

I'm running a simulation with telemac2D, i must put a prescribed flowrates on a boundary. I realised that telemac2D calculate the velocity at the first time step considering the flowrate given, then keeps this velocity fixed at that boundary and change the elevation of water and the flowrate. Is there a method to fixe the flowrate at all time steps for a boundary and not the velocity?

Thank's a lot for responses and tips.

Regards

Hi
You should have a look in the user manual!
For sub-critical flows, when you prescribe the flowrate at a boundary, there is an estimation of the wetted cross section to compute the velocity which satisfy the discharge according to the velocity profile...
This is done at each time step
For super-critical flows you should give the water depth and the discharge as there is no downstream influence on the water level

Thank for your reply,
In my case, i'm in case of a sub-critical flows. So if I correctly understand, if I set the flowrate at a boundary , it leaves the flowrate constant and changes the velocity by estimating the wetted perimeter at every time step. I made a simple case of a channel with a variable bottom at the limits, I made two simulations: one with prescribed velocity and the other with prescribed flowrates, but the result is the same, always, it fixes the velocity and changes the flowrates at each time step for the boundary. You can find my test case in attachments.


Regards

No attachments
But did you only change accordingly the keywords in the steering file and the numbering in the cli file?

Sorry for the attachement it was a mistake. I think changed everything. hope this time the attachements works properly.

Hi,
Here is the problem as a result





TELEMAC2D reacts in the same way by imposing the velocity or the flowrate and i wanted to have the flowrates fixed for my case.

Regards

Hello Omar,

Which release do you use?

I suppose there a few typing mistakes in your steering file (in particular the one with prescribed velocity) because I was not able to run it without minor changes.

Anyway, looking at the output file of your "Q imposed" simulation, you have constant flowrate reached from 2020 s which is coherent with your LIQUID BOUNDARIES FILES.
Flowrate is a value integrated along a surface, not a punctual value at a specific point (I do not know what you printed in your previous message).

If you look at the output file of your "V imposed" simulation, you can see that the flowrate is not as stabilised as the "Q imposed".

Hope this helps,

Chi-Tuan

Hello pham,

thanks for your answer. i think it's clear now. i'm using v8p2, can you please give me the changes that you maid maybe it will help me for other simulations.

Regards

Hello Omar,

The changes are not too difficult to find if you run the steering file you have sent (t2d_littoral_V_imposed.cas):
- LIQUID BOUNDARIES FILE = 'test_V_imposed.liq' (not test_V_impsoed.liq, typing mistake)
- PRESCRIBED ELEVATIONS = 0;0 (uncomment as code 544 in the BOUNDARY CONDITIONS FILE)

Chi-Tuan