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Hi,

I made a model on telemac 2d representing a river with a dam and on right side a supply channel to the turbines.
The purpose of this study is to understand the head loss measured.

I created 15 liquid boundaries : 8 for the barrage valve, 4 for the water supply of the fish pass, 2 for the water supply of the turbines and 1 for the river upstream. Except for the river upstream for witch I provide an entering flow and a water free surface rating, I provide an existing flow for each liquid boundary.

I would like to have your opinion about the results I obtain :
As you can see on the figure joined,

there is a head loss at the entrance of the channel a pressure drop probably related to the reduction of the passage cross-section and the turn and then the free surface elevation rises while the bottom of the channel is flat and even goes down at the end.
I don't understand how it can be possible to have a negative energy slope in this case! Does anyone have an explanation?

Try to avoid mixing between free surface slope and energy slope...

Yes you're right.
But is there an explanation for the rise of the free surface in this case ?

Did you sleep during hydraulic courses at ENSEEIHT?

There is probably low velocities in the reservoir. So there is a transfer from potential energy to kinetic energy in the entrance of the channel which leads to lower water level.
After, when the contraction effect disappear, there is a velocity reduction which leads to a transfer form kinetic to potential and by consequence, a higher water level

This is the same phenomenon you could observe around bridge pile.

Regards

Thank you for your answer and to answer to your question no i didn't sleep during the courses!

I understand that the transfer from potentiel energy to kinetic energy in the entrance of channel wich leads to lower water surface. But after that the channel section is the same so you don't have the same configuration than an bridge pile. I don't see an explanation for the contraction effect disappearance since the passage section of the channel remains the same.

The more trouble thing is that at the end of the channel there is an elevation of the free surface despite the fact that the passage section is kept.

There is an acceleration more important in the left side of the channel so the contraction is more important
At the end of the channel, the bottom decrease so the velocity is lower and then the water level increase

Yes the bottom decrease but it is compensated by the passage section reduction (there is a wall in the middle of the canal). It is normal that the water level increases but here the water level increases to such an extent that the free surface rating also increases, which is confusing!