2nd order schemes only 1st order accurate?

ThinkQuick · September 10, 2012, 06:44

Hi all,

I am running a volume of fluid simulation with highly turbulent (k-epsilon model) water flowing in a 2D domain. I am using the Non-iterative time advancement option with a fractional step. I have set all discretisation schemes to second order (Momentum, Turbulent Kinetic energy and transient formulation) using PRESTO! for pressure and Modified HRIC for VF.

When I check for grid convergence I only get first order convergence. I am unable to check for finer meshes due to computation time. I understand there is inaccuracies associated with both the VOF method and k-epsilon model however there still should be 2nd order convergence.. right??

Any recommendations? I am about to progress and just talk about how 2nd order accuracy could not be obtained due to the complexities of the flow.. is that bad practice?

Thanks for any advice!!!

ata · September 11, 2012, 04:10

Hi
Did you have an orthogonal mesh? I think orthogonality can reduce the order of accuracy. Or may be your mesh is not so fine.

ThinkQuick · September 11, 2012, 05:22

Quote:

Originally Posted by ata

Hi
Did you have an orthogonal mesh? I think orthogonality can reduce the order of accuracy. Or may be your mesh is not so fine.

Thanks for your reply,

Yes I am using a orthogonal mesh. What mesh should I be using?

Unfortunately due to time constraints and lack of resources I am unable to reduce my mesh size any further. It could potentially be the issue, but I feel my mesh is fine enough.

ata · September 11, 2012, 06:16

And what is the maximum aspect ratio in your mesh?

September 10, 2012, 06:44	2nd order schemes only 1st order accurate?	#1
ThinkQuick New Member Join Date: Jun 2012 Posts: 11 Rep Power: 14	Hi all, I am running a volume of fluid simulation with highly turbulent (k-epsilon model) water flowing in a 2D domain. I am using the Non-iterative time advancement option with a fractional step. I have set all discretisation schemes to second order (Momentum, Turbulent Kinetic energy and transient formulation) using PRESTO! for pressure and Modified HRIC for VF. When I check for grid convergence I only get first order convergence. I am unable to check for finer meshes due to computation time. I understand there is inaccuracies associated with both the VOF method and k-epsilon model however there still should be 2nd order convergence.. right?? Any recommendations? I am about to progress and just talk about how 2nd order accuracy could not be obtained due to the complexities of the flow.. is that bad practice? Thanks for any advice!!!

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September 11, 2012, 04:10		#2
ata Senior Member ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 323 Rep Power: 18	Hi Did you have an orthogonal mesh? I think orthogonality can reduce the order of accuracy. Or may be your mesh is not so fine.

September 11, 2012, 06:16		#4
ata Senior Member ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 323 Rep Power: 18	And what is the maximum aspect ratio in your mesh?