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November 25, 2015, 07:19 |
Thanks man
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#21 | |
Member
Baradwaj B S
Join Date: Jan 2015
Posts: 75
Rep Power: 11 |
Quote:
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April 10, 2017, 16:00 |
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#22 |
New Member
Sebastián Barragán
Join Date: Apr 2016
Location: Bogotá, Colombia
Posts: 14
Rep Power: 10 |
Hey!
I'm trying to load a previous result (steady state) done in a coarse mesh into a finer one, but it seems it doesn't work... I read that I should drop the URF at least for the first iterations, which I did, but then when setting the default ones again, the solution crashes. Do I have to run the whole calculations with lower URF? Cheers! |
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September 25, 2017, 12:59 |
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#23 | |
Senior Member
Reviewer #2
Join Date: Jul 2015
Location: Knoxville, TN
Posts: 141
Rep Power: 11 |
Quote:
Isn't that SIMPLE family algorithm overshoot velocity instead of pressure? |
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February 20, 2020, 05:07 |
Effect of URF on Solution
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#24 |
Member
Vignesh Lakshmanan
Join Date: Nov 2016
Posts: 79
Rep Power: 10 |
Hi All,
I am solving a natural convection problem (Transient). Aim is to find the temperature drop within a volume in 2 hours. I am using Fluent for the simulations. What I am observing is that the transient behaviour is different when I use different values for solution controls. In Picture 1.png, I have used default values for Solutions controls, whereas in Picture 2.png, I have under relaxed Body forces and Energy to 0.8 (Default: 1). There is no other change in the case/mesh/geometry. Now, can someone explain what is happening here and which is correct. As per my understanding, the Solution controls are for faster / slower convergence and stability issues. They should not affect the solution |
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February 20, 2020, 05:26 |
URFs
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#25 |
Senior Member
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You are right; URFs are meant for stability and do affect the convergence rate. But they also behave like diffusion controls. In other words, if very low URFs are used, it takes more iterations for a field to reach not just convergence but also conservation. Energy time scales are larger, i.e., it takes longer for thermal energy to diffuse. Therefore, higher URFs are used for it. When lower URF is used, it would require more iterations to reach same conservation level. So, you have to ensure that when URF is reduced, you run for more iterations in each time-step and convergence target for energy is achieved. You may also reduce the convergence target to 1e-7.
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Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
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February 20, 2020, 05:54 |
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#26 | |
Member
Vignesh Lakshmanan
Join Date: Nov 2016
Posts: 79
Rep Power: 10 |
Quote:
The energy residual has converged to 1e-7. You mean to say, if I use higher number of iterations per time step, my profile in 2.png will be similar to 1.png? If that is the case, then it is incorrect because experimental data follows a profile similar in 2.png. Regards VL |
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February 20, 2020, 05:56 |
Implications
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#27 |
Senior Member
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What I mean is whether you use low URF or high, you need to ensure that the convergence within each time-step is good. If you are getting wrong results with high URF for energy, most likely the time-step used is higher than expected.
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Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
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February 20, 2020, 06:01 |
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#28 | |
Member
Vignesh Lakshmanan
Join Date: Nov 2016
Posts: 79
Rep Power: 10 |
Quote:
Yes, my time step is in fact pretty high. But I have used it in purpose because it was not creating problems like these in the past. I have also validated results with different time steps and I am using the one which gives me the results at the earliest. Anyways, thanks for the reply. Regards VL |
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February 20, 2020, 07:38 |
Sensitivity
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#29 |
Senior Member
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Most of the time, users do a grid sensitivity analysis, but it is incomplete. Grid is spatial as well as temporal. By grid sensitivity analysis, users usually imply spatial. However, temporal is equally important.
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Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
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September 4, 2020, 08:37 |
Residuals smooth, crazy, smooth
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#30 |
New Member
José Ramón Quiñonez Arce
Join Date: Oct 2017
Location: Leeds, UK
Posts: 17
Rep Power: 9 |
Hi. I am simulating non premixed combustion with propane for stabilisers, I reduced my URF as specified in the manual, however left the momentum and turbulence DR as 0.8. My residuals went down pretty well, and then after 150 iterations they went up for at least 300 more iterations. However after 450 iterations they are normalising, and then they go down smooth again. Does this affect my solution? I am using a 3D model with more than 4 M nodes, realisable kE, and laminar flamelet.
Thanks! |
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September 6, 2020, 02:06 |
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#31 | |
Member
Vignesh Lakshmanan
Join Date: Nov 2016
Posts: 79
Rep Power: 10 |
Quote:
Regards Vignesh |
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