open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi,

I want to simulate the flow field in a meandering river. I just installed version 7 to implement secondary current effects. I choose the default values:
SECONDARY CURRENTS = YES
PRODUCTION COEFFICIENT FOR SECONDARY CURRENTS = 7
PRODUCTION COEFFICIENT FOR SECONDARY CURRENTS = 0.5

My simulation is running but it exceeds the maximum iterations. I am wondering how to solve this problem and to with values I can change PRODUCTION COEFFICIENT FOR SECONDARY CURRENTS and PRODUCTION COEFFICIENT FOR SECONDARY CURRENTS.

Kind regards,
Veerle

Hello,

Our specialist will be back next Monday. Waiting for him please first check that the simulation is running without adding the secondary currents. Then if adding the secondary currents effect causes a problem try to decrease the time-step.

With best regards,

Jean-Michel Hervouet

Hi,

I decreased the time step and now it works. But I am still wondering what the effect is of both parameters and in which range they vary.

Thanks,
Veerle

Dear Veerle,
thanks a lot for your post.
Please find below some comments for your questions:

The PRODUCTION COEFFICIENT FOR SECONDARY CURRENTS determines the rate of vorticity production. Experimental evidence suggests that this coefficient should be in the larger than 5. This coefficient is associated with the advection of vorticity.

The DISSIPATION COEFFICIENT FOR SECONDARY CURRENTS determines the rate of vorticity dissipation. This coefficient is in general set to 0.5. This coefficient is associated with the lateral diffusion of the streamwise vorticity owing to turbulence.

Bernard and Schneider (1992) suggested that the values of both empirical coefficients must be established by trial-and-error comparison of predicted and measured velocities.

You can therefore use the suggested values (by default) as starting point for further calibration and improvements.

I hope it helps,

Cheers,

Pablo

Dear Pablo,

Thanks for the explanation. I tested the defaulf values and this gave good results. I also tested some other combinations:

Values of 15 and 20 for PRODUCTION COEFFICIENT FOR SECONDARY CURRENTS gave unstable results. The difference between 5 and 7 (default) nearly differed from eachother.

Values 0.1, 0.5 and 1 for the DISSIPATION COEFFICIENT FOR SECONDARY CURRENTS are very similar.

I am simulation morphological changes as well. I tried to combine the secondary current correction in both sisyphe and telemac2d but this didn't work. Do I have to choose if I want the correction in telemac2d or in sisphe? In the end I want to compare the measured and simulated morphology.

Kind regards,
Veerle

Hi, Veerle.
I'm on mophological changes in meandering flow like you.
and Could I know about your result related with combining the secondary current correction in both sisyphe and telemac2d?
Should you choose telemac2d or sisyphe for that function?

Kind regards,
Noah.

Dear Noah,

So far I only performed simulations with secondary current either in telemac2d or sysiphe.
As far as I know, the secondary current correction represents other processes in sysiphe and telemac. I think you should do the simulation with SC correction seperately in telemac and sysiphe and then combine the effects. And see which corrections represent best your situation.

SC is a very new feature so I aspect to have more info on this in the future.

Good luck,
Veerle