[Yiran]

Dear all, I met one problem when I was trying to simulate a double-lance for hydrogen and coal (conveying gas N2) injection and combustion in a pipe. The simulation conditions are as followed:

• The inner diameter of the two lances: 35mm;
• The diameter of the pipe: 250mm (inlet) down to 145mm (outlet);
• The mass flow rate of H2 in one lance: 0.096 kg/s 298K 1atm;
• The mass flow rate of N2 in the other lance: 0.011 kg/s 298K 1atm;
• The mass flow rate of air injected from the inlet of the pipe: 3.423 kg/s 1451K 1atm;

ERROR #001100279 has occurred in subroutine ErrAction.
| Message: |
| Floating point exception: Overflow

I tried to refine the mesh, now it is 555158 mesh element.
I tried to reduce the timestep, now it is 0.005s.
But I still met the same error msg.
I tried to use 100% N2 in both lances, the case run well.
I guess I should give different settings (special consideration) for H2 injection.
May I have your idea of dealing with it?

Thank you very much.

[ghorrocks]

FAQ: https://www.cfd-online.com/Wiki/Ansy...do_about_it.3F

Note refining the mesh will make it more unstable, not less.
Reducing the time step will help, but may not fix it.
If the simulation runs OK with N2 in both lances then try to think about what happens when you use the actual gasses compared to N2. Things to think about are acoustic velocity differences (is the hydrogen choked?), or how the pressure waves act when the lance jets combine.

[Yiran]

Originally Posted by ghorrocks

FAQ: https://www.cfd-online.com/Wiki/Ansy...do_about_it.3F

Note refining the mesh will make it more unstable, not less.
Reducing the time step will help, but may not fix it.
If the simulation runs OK with N2 in both lances then try to think about what happens when you use the actual gasses compared to N2. Things to think about are acoustic velocity differences (is the hydrogen choked?), or how the pressure waves act when the lance jets combine.

Thank you very much, I will have more try from the aspect of pressure.

[ghorrocks]

Please read the FAQ as well. Because your question is asked very frequently.

[Yiran]

A following question, I found the main problem of overflow is related to a very high Mach number. May I ask your idea of dealing with it?
I changed the turbulence model from Medium to High, but it didn't work.

Thank you very much.

[ghorrocks]

An unrealistically high Mach number is usually the sign of divergence, and the divergence will eventually lead to an overflow error. So this is just a different symptom of the same problem, it is nothing new. Again, the details of what to do are in the FAQ so please read it.

[Yiran]

Originally Posted by ghorrocks

An unrealistically high Mach number is usually the sign of divergence, and the divergence will eventually lead to an overflow error. So this is just a different symptom of the same problem, it is nothing new. Again, the details of what to do are in the FAQ so please read it.

Thank you very much. On it now.