Learning Forum

[ALEXANDRE COSTA]

Hi All,

I am having divergence issue after 0.3 s (around 30000 iterations) for a transient run in Fluent:

[Rob]

That's been struggling for the last several time steps. Assuming you have the data file saved have a look at what's going on. I suspect something is changing more quickly than the time step can resolve, so it's probable that you'll want to reduce the time step. For P-V coupling you may find PISO to be more efficient, the PBCS doesn't give much (if any) benefit on a transient run.

[ajain707]

I used PISO , and calculated time step from strouhalt number, my calculations always has a floating point exception because the solution diverges. 
I am simulating a water cooled cold plate and I am using a udf for my heat flux (heat flux varies with time and i imported a text file).

[Rob]

Turn off the UDF and see what happens - when models fail always switch off models until it works, then work out which model(s) cause the problem. 

[ajain707]

It works when i input a constant value for heat flux. I import my data from a txt file (using the read-transient-table function), i don't know how to diagnose what is wrong with that process

[ajain707]

this is the data i use for getting the values

[Rob]

Ah, you want to use a transient profile and not have repeat values in the time column - use an extra decimal place when you alter the formatting to suit a profile.