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Hi everyone,

I would like to open a discussion here about how to get a stabilized model when you simulate a supercritical regime at the entrance of your model.

I am modeling a very steep spillway channel of a dam for a safety flood. Therefore, my regime is very turbulent and supercritical and I have difficulties getting stabilized results.

I tried several technics, so far:
- reduce the calculation time step
- impose a water elevation at the entrance
- Use velocity distribution 4 or 5
- Apply a higher than expected water surface elevation as initial condition
- Create a fake flat channel upstream of my real entrance that would allow a subcritical flow at the entrance of the model and then let telemac 2D deal with the transition to a supercritical regime

Is there other things I could do ? Which one has been working best for you ?

Thanks in advance for your input!
Nicolas.

Hi Nicolas,

You should take in account that for supercritical flow at inlet two conditions are needed, you have to prescribe discharge and elevation.

I hope it helps,

Cheers,

José Morales

Hi,


What I have done is to create stretches at the beginning and at the end where a subcritical condition is obtained.

What I would like to know is, if the problem of modeling the supercritical flows is the instability of the equations, until what number of range of Fr is allowed to model without having problems?

Cheers

Hi,

What kind of Instabilities? Are you prescribing both Q and H at inlet? Sometimes you could use thompson boundary option (In the case of Ill posed outlet).

About Fr number, I have work with a maximum value of 5 in my experience and does not have incidence on the results, but i do not know which range would be okay for the equations (sometimes a small time step makes more difference than a lower Fr).

What is your highest value of Courant?

Cheers,

Jose

Jose,

My doubt, it comes from that it is not advisable to use supercritical conditions in edge conditions, Why? I think it's due to the instability of the problem, I really do not know.

You tell me you have input conditions with Fr = 5 and you have no problems? If so, thank you for the information.

The maximum current I use is less than 0.5, as recommended.