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-   -   Fluidized bed failure (http://www.cfd-online.com/Forums/cfx/70005-fluidized-bed-failure.html)

Carlitos November 11, 2009 12:42

Fluidized bed failure
 
1 Attachment(s)
Hi,

Im simulating a fluidized bed model. I'm carrying out this simulation with Ansys CFX 11.0 software but i'm not able to find out the cause of error in solver. Besides, the cfx5solver finishes with a crash file in the beginning of the iterations so i cant get a backup file in order to check how the model is being simulated. The error is the following one:

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

Details of error:-
----------------
Error detected by routine POPDIR
CRESLT = ILEG

Current Directory : /FLOW/NAMEMAP

I've read in forums that this error means the simulation is diverging. In order to make the simulation more stable I have chosen all these options:

- a laminar model
- remesh again and again to improve the mesh quality,
- reduce timestep size
- reduce convergence criteria
- use the 1st order discretisation
- check my initial conditions

I don't know what to do to come across this error so if you kindly try to help me..Thank you in advance.

Carlitos

(I've also attached the txt file, if you want you can look at it)

ghorrocks November 11, 2009 22:13

Try to add the physics one step at a time. Start off with a simple single phase flow, then add the physics in as small steps as possible checking everything works.

ckleanth November 12, 2009 06:16

you can add " backup file at start = t " in the EXPERT PARAMETERS section to test the IC

do not use the Kinetic Theory model but the standard gidaspow solid pressure model and small timesteps.

you dont need adaptive mesh before you even managed to get the model started, a uniform mesh with reasonable resolution is much preferred. try first the physics setup on a 2D model and as glenn said add a bit of complexity at a time.

Carlitos November 12, 2009 13:30

Ok, thank you ghorrocks and ckleanth. Let me try what you said to me.. If i cant solve the problem ill post again.

Carlitos

Carlitos November 23, 2009 14:30

Fluidized bed II
 
Hi

I've added the physics little by little as you advised me and now i manage at getting a simulation with the following main characteristics:

- Laminar flow
- Gidaspow drag model (which includes Ergun and Wen&Yu correlation)
- None Kinetic theory

Although bubbles are created inside the fluidized bed, the problem is the maximum packing: I've noticed that the solid volume fraction can become greater than the maximum packing limit (which i've fixed previously). This should be impossible. I dont know how to overcome the problem. I've tried to set as initial condition a value a bit lower than the maximum packing, but it doesn' t work. What do you suggest?

Another problem i have is the use of Gidaspow solid pressure as you mention above. I don't know which values for compaction modulus use. Could you help me?

Thanks in advance,

Carlitos

ckleanth November 24, 2009 20:30

if you need more help with the model I would reccomend you to buy the gidapsow book.

ansys have compiled a custom executable for me to help with divergence. I suppose if you have a suport contract you can request them to make one for you. otherwise use a lot more smaller timesteps

germangsilva July 28, 2010 14:28

hi Carlitos

I'm doing studies of fluidization (gas-solid), I'm using cfx11 or 12, and applying LES, but I have great difficulty setting the program cfx, I ask your help please. my email is germangsilva@gmail.com

germangsilva July 28, 2010 14:54

fluidized bed - CFX
 
hello

I'm doing studies of fluidized bed (gas-solid), I'm using cfx11 or 12, and applying LES, but I have great difficulty setting the program cfx, I ask your help, please. my email is germangsilva@gmail.com.

with Regards

pannsave July 28, 2010 17:14

Hi Carlitos

I think you need not specify two domains for fluidised bed simulation, you can define initial condition for packed bed and freeboard regions using CFX Expression Language by specifying solid volume fraction with function height of column

Another point is you can still reduce time step in the range of 1e-6 and check the simulataion
especially when you incorporating kinetic theory of granular flow model for solid phase, use very smaller time step


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