[thamerS]

Hello everyone,

Am working on a simulation implying a rigid body,
Actually, am receiving a warning on CFX solver saying:

''WARNING: Rotational degrees of freedom have not converged.
Maximum number of iterations exceeded.
Rigid Body: Rigid Body 1
Number of Iterations: 26
Residual on Angular Momentum Equation: 8.36441E-02''

the solver doesn't stop as it's not a major problem, when going on CFD-post I can clearly see the body rotating,
I don't know if this kind of warning may cause the divergence of my simulation.

Any help would be very appreciated,
Thanks in advance

[aero_head]

Hello Thamer,

What is the Courant number/CFL for the simulation?

[thamerS]

Originally Posted by aero_head

Hello Thamer,

What is the Courant number/CFL for the simulation?

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Hey,
i just stopped the simulation because it's not converging, and here's the average scale information:


RMS Courant Number = 7.2565E+01
Maximum Courant Number = 6.4815E+02

[aero_head]

Hello Thamer,

Those seem pretty high, possibly the cause of the divergence. What time step size are you using for your simulation, and what is your smallest grid node size?

I ask because the CFL criteria is

< 1

Where is the difference in time step size and is the distance between grid node elements.

From my understanding, from theory, if the Courant number is <=1, fluid particles move from one cell to another within one time step (at most). If it is >1, fluid particles move through two or more cells at each time step and this can affect convergence negatively.

In general, lower time step to lower Courant number, raise time step to increase Courant number. The distance between grid node elements also plays a role as well, as per the equation.

Another cause for the divergence may be poorly set boundary conditions. So, if you give us information on:
1. The selected time step size,
2. The min/max grid node element size and
3. The boundary conditions you used
we may get a better sense of what the cause of the divergence is.

[thamerS]

Originally Posted by aero_head

Hello Thamer,

Those seem pretty high, possibly the cause of the divergence. What time step size are you using for your simulation, and what is your smallest grid node size?

I ask because the CFL criteria is

< 1

Where is the difference in time step size and is the distance between grid node elements.

From my understanding, from theory, if the Courant number is <=1, fluid particles move from one cell to another within one time step (at most). If it is >1, fluid particles move through two or more cells at each time step and this can affect convergence negatively.

In general, lower time step to lower Courant number, raise time step to increase Courant number. The distance between grid node elements also plays a role as well, as per the equation.

Another cause for the divergence may be poorly set boundary conditions. So, if you give us information on:
1. The selected time step size,
2. The min/max grid node element size and
3. The boundary conditions you used
we may get a better sense of what the cause of the divergence is.

Hey Kira

i looked after what u mentioned and yeah, i think my meshing is too small concerning the time step that am selecting.
Am gonna try to go with a big very big mesh in order to see if my code is working right or no.
If you're interested we may have a call or screen share within teams to discuss that.
Thanks