Divergence detected in AMG solver : k

littlebroca · March 8, 2011, 05:57

hello,

I am currently trying to simulate a water flow into a nozzle for a atomisation. It's an internal flow with very small dimensions.

I am using the VOF method, with the water flow going through the air. Transient flow and turbulent (Realizable k-epsilon) are my conditions.
I have a Reynolds (for the Inlet) of about 3500.

I used a velocity inlet and pressure outlets. I used the turbulent intensity (that i calculated as a 5,7%) and turb viscosity ratio (that is around 12%)

My time step is 5e-7s, but my calculation always seem to diverge. (It says for the initialization that the courant number is around 3, but it gets very quickly to a higher number than the 250 bar over which Fluent doesn't continue)

Do i just adjust manually the under relaxation factors ? Is there may be something that some of you might help me with ?

Thank you in advance.

Tarik.

f0208secretx · May 13, 2011, 02:31

I have encountered a similar problem... adjusting the under relaxation factor doesn't seem to work on me.

March 8, 2011, 05:57	Divergence detected in AMG solver : k	#1
littlebroca New Member Tarik Bennani Join Date: Oct 2010 Posts: 6 Rep Power: 18	hello, I am currently trying to simulate a water flow into a nozzle for a atomisation. It's an internal flow with very small dimensions. I am using the VOF method, with the water flow going through the air. Transient flow and turbulent (Realizable k-epsilon) are my conditions. I have a Reynolds (for the Inlet) of about 3500. I used a velocity inlet and pressure outlets. I used the turbulent intensity (that i calculated as a 5,7%) and turb viscosity ratio (that is around 12%) My time step is 5e-7s, but my calculation always seem to diverge. (It says for the initialization that the courant number is around 3, but it gets very quickly to a higher number than the 250 bar over which Fluent doesn't continue) Do i just adjust manually the under relaxation factors ? Is there may be something that some of you might help me with ? Thank you in advance. Tarik.

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May 13, 2011, 02:31		#2
f0208secretx Member J.-H. Wang Join Date: Oct 2010 Posts: 72 Rep Power: 16	I have encountered a similar problem... adjusting the under relaxation factor doesn't seem to work on me.