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Solver aborts due to high Ma-Number

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Old   June 5, 2018, 12:42
Default Solver aborts due to high Ma-Number
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Hello everybody

I have a question about the error message "Overflow" and have already read the FAQ sheet. My problem is, that when I solve a certain simulation, the residuals do a quite good job and everything seems "normal". After a certain iteration (around 50 to 80) the Mach Numbers becomes high (Ma>2 in most cases) and in the following iteration the solver aborts. The region of high Ma-number could be located in the hexa mesh and the timescale was adjusted that in this region a Courant Number of (more or less) 1.0 exists. So, it seems that this might be a numerical problem. Therefore I would like to ask, if someone already had this kind of error and have a solution / suggestion, what this problem could cause.

Thank you everybody for help!
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Old   June 5, 2018, 13:13
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I assume you are running Total Energy model.

Have you also activated the Viscous Work Term?

How about the High Speed Wall Function Model?
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Old   June 5, 2018, 14:02
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Quote:
Originally Posted by Opaque View Post
I assume you are running Total Energy model.

Have you also activated the Viscous Work Term?

How about the High Speed Wall Function Model?
Thank you for your reply, Opaque.
That is correct, I'm running the Total Energy model.
Yes, I've activated the Viscous Work Term.
No, currently I've disabled the High Speed Wall Function Model. Do you suggest, that this might help me solving my problem and is the reason for the solver's abort?

It also has to be said, it is a matter of multiphase flow and the velocities are faraway from being in a "critical" mach region.
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Old   June 5, 2018, 16:45
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Are you running with a rotating frame?

If you are running in the stationary frame and multiphase flow, I would start with the Thermal Energy model.

I would not use the High Speed Model unless you know why it is needed, and what the benefits are.

The typical advice for complex simulations, multiphase flow qualifies as such, is to start simple.

Last edited by Opaque; June 5, 2018 at 18:36.
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Old   June 5, 2018, 18:14
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Remember that in multiphase situations, the speed of sound is usually much lower than for single phase situations. So your Critical Mach Region might be closer than you think.


Follow the advice of Opaque: Start Simple.
After a succesfull simple run, you can always proceed with more complexity
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Old   June 6, 2018, 12:04
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Thank you guys for your answers and advices!

Quote:
Originally Posted by Opaque View Post
Are you running with a rotating frame?

If you are running in the stationary frame and multiphase flow, I would start with the Thermal Energy model.

I would not use the High Speed Model unless you know why it is needed, and what the benefits are.

The typical advice for complex simulations, multiphase flow qualifies as such, is to start simple.
No, I'm not running with rotating frame. The analysis type is stationary and also the frame is a stationary frame. Due to the air is compressible, I thought I should air let be in the Total Energy Model. Water, my second fluid, is setup with the Thermal Energy model.
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Old   June 6, 2018, 12:16
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How much of the compressibility effects do you need to model?

As said before, simple. I would start with Air @ 25C (incompressible), Thermal Energy. If the model runs w/o a problem, check the flow solutions and estimate the Mach number present in the solution, and decide the next step.

Recall the goal is to obtain a base solution so you can build with confidence from there.
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