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Fluent giving different results for the same analysis |
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August 15, 2014, 03:14 |
Fluent giving different results for the same analysis
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#1 |
New Member
Burak Kaya
Join Date: Nov 2011
Posts: 21
Rep Power: 14 |
Hi,
I'm analysing a 2d model of a centrifugal pump using steady k-epsilon turbulence model. I iterate the fluent 5000 times. I use 2d mode, not 2ddp. Residual convergence criteria is 1e-5 for k,epsilon, x velocity, y velocity, continuity. I get different results each time I run the model. What could be the reason? Should I increase the number of iterations, or decrease the convergence criteria? Thanks in advance. |
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August 15, 2014, 03:43 |
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#2 |
New Member
Burak Kaya
Join Date: Nov 2011
Posts: 21
Rep Power: 14 |
I'm changing the option to 2ddp to see if it solves my problem.
Edit: It didn't solve my problem. |
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August 15, 2014, 03:53 |
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#3 |
Senior Member
Join Date: Nov 2013
Posts: 1,965
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What do you mean with "different results". Slightly different or completely different?
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August 15, 2014, 06:27 |
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#4 |
New Member
Burak Kaya
Join Date: Nov 2011
Posts: 21
Rep Power: 14 |
Pressure values are 10% or so different for the same setup(same .msh file).
I use a velocity inlet, a pressure outlet, and wall boundary condition at the blades. I want to use the result for an optimization work. |
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August 15, 2014, 07:06 |
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#5 |
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
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The equations you solve for are deterministic. For a given set of initial conditions you will always get the same result. Obviously, you do something (unintentionally) different each case you run it.
__________________
The skeleton ran out of shampoo in the shower. |
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August 15, 2014, 10:22 |
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#6 |
New Member
Burak Kaya
Join Date: Nov 2011
Posts: 21
Rep Power: 14 |
I think I spotted the problematic portion of the journal file:
----------------------------------------------------------- yes "C:\Users\bpehlivan\Desktop\2dpump\ga17\mass_flow_ rate_v2.flp" re/si a-w-a 2 6 total-pressure yes "C:\Users\bpehlivan\Desktop\2dpump\ga17\total_pres sure_v2.srp" re/si q exit yes ----------------------------------------------------------- I'm getting the following message on fluent when I run the fluent journal file: -------.-.-.--.-.------.--..-.--.-.---.-.------.--.-.-.- > re/fl/mf all boundary/interior zones [yes] no Zone(1) [()] 5 Zone(2) [()] 9 Zone(3) [()] Write to File? [no] yes filename (*.flp) [""] "C:\Users\bpehlivan\Desktop\2dpump\direct1\mass_fl ow_rate_v2.flp" > re/si /report/surface-integrals> a-w-a () surface id(1) [()] 2 surface id(2) [()] 6 surface id(3) [()] area-avg of> total-pressure Write to File? [no] yes filename (*.srp) [""] "C:\Users\bpehlivan\Desktop\2dpump\direct1\total_p ressure_v2.srp" /report/surface-integrals> re/sinvalid command [re] i /report/surface-integrals> area flow-rate sum area-weighted-avg integral vertex-avg facet-avg mass-flow-rate vertex-max facet-max mass-weighted-avg vertex-min facet-min standard-deviation volume-flow-rate /report/surface-integrals> -------.-.-.--.-.------.--..-.--.-.---.-.------.--.-.-.- So, I think there is a problem when writing the pressure to the file. |
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August 15, 2014, 10:25 |
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#7 |
Senior Member
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Change it to "/re/si". I think that should work for you.
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