setting Timestep

Cecco · May 27, 2013, 09:31

Hi everybody,
I'm running a steady simulation of a centrifugal blower.
Usually I do the following:
1. I set a really small timestep order to E-06 with Upwind scheme;
2. after 1000 iterations I switch timestep to E-05 with upwind scheme;
3. when physical properties which I monitor are stable, I switch to Blend Factor =0.75 (so not completely High resolution) and wait for a new stable state.

This process usually works, but not now.
Until I use upwind solution seems reach the convergence, but when I switch to Blend factor 0.75 ( i tried 0.6 as well) it doesn't happen.
I changed a lot of timestep between E-5 and E-7, but seems no works.
Someone has an idea about this behaviour and about what I should do?

Thanks

ghorrocks · May 27, 2013, 19:50

This is typical behaviour when you switch to a more accurate discretisation scheme. It means your simulation is not very numerically stable. In your case this probably means you need better mesh quality.

Cecco · May 28, 2013, 04:08

I'll do a new mesh.
Thanks man. U precious!

May 27, 2013, 09:31	setting Timestep	#1
Cecco Member Francesco Join Date: Jan 2012 Posts: 31 Rep Power: 14	Hi everybody, I'm running a steady simulation of a centrifugal blower. Usually I do the following: 1. I set a really small timestep order to E-06 with Upwind scheme; 2. after 1000 iterations I switch timestep to E-05 with upwind scheme; 3. when physical properties which I monitor are stable, I switch to Blend Factor =0.75 (so not completely High resolution) and wait for a new stable state. This process usually works, but not now. Until I use upwind solution seems reach the convergence, but when I switch to Blend factor 0.75 ( i tried 0.6 as well) it doesn't happen. I changed a lot of timestep between E-5 and E-7, but seems no works. Someone has an idea about this behaviour and about what I should do? Thanks

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May 27, 2013, 19:50		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	This is typical behaviour when you switch to a more accurate discretisation scheme. It means your simulation is not very numerically stable. In your case this probably means you need better mesh quality.

May 28, 2013, 04:08		#3
Cecco Member Francesco Join Date: Jan 2012 Posts: 31 Rep Power: 14	I'll do a new mesh. Thanks man. U precious!