divergence detected in AMG solver pressure correction,fluent典型错误 - 图文

问题：8-31-rke-steady-4-0.8运行至11000迭代步是报错“divergence detected in AMG solver: pressure correction”（补充：每个工况均遇到此类情况，原因尚未找到，暂时解决办法是将压力松弛因子从0.3改为0.1）；

This error is reported when Fluent is not able to converge the solution。The residuals are not converged。This error may come due to various reasons like improper mesh，improper boundary conditions，wrong material and improper solution settings。It is advisable to re check the entire case when one encounters this error。

解答：

以上老外对这个问题的回复，确实很多客户遇到过这样的问题，原因是多方面的，主要原因集中在网格质量差和边界条件的不合理。

对于你的问题，如果之前都没有错误，到一定计算步才出现这样的问题，说明不是边条的问题，问题可能出在局部的网格上面，你将压力松弛因子调小，增加跌代次数，减小了误差，是解决问题的方法之一。

如果想彻底回避这样的问题出现，建议在网格上还需要下点工夫！ 附：老外对类似问题的回复，你可以参考一下。

I try to study the turbulence inside a vertical cylinder. In a first time, I take the case of steady flow. The air is introduced axially from below, deflected by means of a small conical deflector and thanks to the geometry of the chamber the air goes up into the cylinder. I take the ideal gas law, k-epsilon model, inlet and outlet pressure for boundary conditions. My problem is that I have directly the message \detected in AMG solver : k when I want to iterate. I try a lot of solutions I have find in this forum without any result. Could anyone help me? Thanks

in advance Check your hardware, especially RAM sockets. I have experience, that this could be initiated by some bad memory address sectors.

I had a similar problem, but with pressure correction. I found that I had some highly skewed cells. Once I corrected the highly skewed cells by adapting the iso-values of cell skewness my case began to iterate.

Perhaps this may be your problem. First initialize the solution and then go to contours grid and select equiangle skew and click compute to get you min and maxs. Having skewed cells of 0.9 or higher isn';t good, as in my case.

Hope this helps I have check the skewed cells but it appears that in my case, this number is lower than 0.4 Is it too high?

Hi. I have a simulation of a supersonic-valve running but the program shows me this message: divergence detected in AMG solver: temperature I tried to rise the limits for temperature and other solution limits but nothing has helped so far Does anyone what to do thanks

Try to use more conservative Under-relaxation factor. I had the same problem with a wing in a transonic flight. According to me the segregated solver is not suitable for the conditions with high compressibility. Let me know if you succeed in using the segregated and how...

I suggest using the coupled solver，Your problem will vanish... Hope to hear good news from you soon.

Luca this will be something wrong with the either boundary condition or with model selection, generally if things are right fluent just converges fine without any warning or problem.

in my opinion these are the signs that you are doing something wrong in setting up the case, look closely

Hi, I have the same problem, and couldn't solve it by using the coupled solver. Is there any other possible way. I am simulating office room problem. It seems very simple but on every stage it is creating problems for me. I am going to try to change the underrelaxation. lets see what comes up.

Thanks long ago, one of my friend was doing CFD analysis of a kitchen,, using coupled solver, and he faced the same problem, for some time he didn’t get the converged results. Finally when I looked at his mesh. It seemed the problem is with the mesh not with the solver settings. I suggested him to make mesh more finer, and viola it gave results in one run, without any problem. so moral of the story check your mesh.

My mesh is quite fine, but I will try more finer mesh. Thanks then it shall

converge ..anyway have you tried using segregated solver, how the results with that Error: Divergence detected in AMG solver? Posted By: frank Date: Sun, 16 Jan 2005, 3:58 p.m. What does mean and how do i fix it? I am runing a rosseland radiation model and it wont run past 1 iteration.

Frank you are using the segregated solver, so you must reduce the under

relaxation factor as you can. You could have a grid issue concerning high skewness. This can be checked by going to contours grid cell equiangle skew and select compute and check the min and max. You should be below 0.9. If over then this could be your problem. It has happened to me a couple of times. thanks a million i will try this... frank AMG solver: k divergence? Posted By: Robert Date: Sun, 9 Mar 2003, 11:23 a.m. How do I remedy a divergence with this message. This is for scramjet combustion in 2D with injectors on both the top and bottom. Is there any way to look up error messages?

reduce underalaxtion factor.

I have tried reducing the underelaxation factors but the divergence persists. Any other suggestions? Perhaps in the AMG solver Menu? It looks like a problem with your boundary conditions, be sure they're compatible with each other and consistent with the physics of what you';re trying to simulate, I think you'd better don't touch anything in the AMG menu, unless you know exactly what you're doing, It is my opinion, if this could help.

请求高手指点：循环流化床中非稳态气固两相流计算，使用欧拉双流体模型，K-E湍流模型，网格质量<0.55。先计算了层流稳态，残差小于0.01时转为湍流

非稳态。计算时总是出现divergence detected in AMG solver:pressure correction。收敛因子已经调小，请求高手指点。万分感谢！

如果你的网格质量没有问题（ The skewness must be less than 0.85 for Quad/Hex and 0.9 for Tri/Tet cells），那就可能是压力速度耦合方式的问题，你也可以检查下你的压力插值格式是否适合多相流计算；也有可能是边界条件设置的问题。

下面是http://university.fluent.com论坛上的回答，我觉得讲的挺有条理的，这个是可压缩计算出现这个警告的解决回答，你看看对你有用的方面就行了。

Well, this message shows that the run is diverging, namely in pressure correction equation (Sec. 25.4.3 Pressure-Velocity Coupling of Fluent Users Guide). It's hard to tell why this is happening without checking your case.

Are you following some of the solution convergence steps mentioned in this page?- http://www.fluentusers.com/fluent/doc/ori/html/ug/node426.htm#sec-rotref-solstrat Other suggestions I can make -

(1) What pressure-velocity coupling scheme are you using? I found that switching to PISO and turning on skewness correction sometimes helps on skewed meshes. (2) What's the under relaxation factor for temperature (energy)? I find it helpful to reduce it to 0.8-0.9 in problems involving high-speed compressible flows. A coupled of other thing that comes to mind:

(3) FMG initialization may help (Sec. 25.15 Full Multigrid (FMG) Initialization). http://www.fluentusers.com/fluent/doc/ori/html/ug/node1038.htm

(4) Precision issue. What is the minimum cell volume (Grid - Check)? If it's less than 1e-06, then double-precision solver is recommended. density based适用于可压缩流,

pressure based适用于不可压缩流.Z8M

density based把density作为主要变量之一。但不可压时density是常数（一般加入假想的人工可压缩性，来减缓这个矛盾）]

一般来讲，Pressure-Based Solver是Fluent的优势，它是基于压力法的求解器，使用的是压力修正算法，求解的控制方程是标量形式的，擅长求解不可压缩流动，对于可压流动也可以求解；Fluent 6.3以前的版本求解器，只有Segregated Solver和Coupled Solver，其实也就是Pressure-Based Solver的两种处理方法； Density-Based Solver应该是Fluent 6.3新发展出来的，它是基于密度法的求解器，求解的控制方程是矢量形式的，主要离散格式有Roe，AUSM+，该方法的初衷是让Fluent具有比较好的求解可压缩流动能力，但目前格式没有添加任何限制器，因此还不太完善；它只有Coupled的算法；对于低速问题，他们是使用Preconditioning方法来处理，使之也能够计算低速问题。

你说的Density-Based Solver下肯定是没有SIMPLEC，PISO这些选项的，因为这些都是压力修正算法，不会在这种类型的求解器中出现的；建议你还是使用Pressure-Based Solver解决你的问题。

在你启动Fluent的时候不就有个2d，2ddp，3d，3ddp的选项吗？2ddp就是双精度的。

pressure-based solver里面的压力速度耦合方法，在solve->control里面设置，pressure-velocity coupling。

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