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[求助]
燃烧计算，先收敛后发散
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我做加热炉的燃烧模型，计算过程中收敛的挺好，在收敛快结束的时候能量方程开始发散，然后出错终止。 我这个模型网格数多一点，有一百七十万，不知道跟网格数或者问题的复杂程度有关系吗？ 请高手予以解答，感激不尽~~ |
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6楼2012-11-28 19:15:01
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xiegangmai: 金币+2, 谢谢参与 2012-11-28 22:03:31
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用Fluent算过非预混燃烧，CFX还没试过，看看这个对你有没有用... 9.17.1. General Procedure for Running Simulations For many cases, such as the Combustion Tutorial, the run can be started using automatic initial guesses for most fields and the choice of model in the first part of the tutorial, (EDM) is the most robust of the combustion models. If you are having trouble getting a complex problem to converge, the following steps may aid convergence: Begin by specifying a single step reaction using the Eddy Dissipation Model. For initial conditions, specify Oxygen with a mass fraction of 0.232 and set each of the other species to Automatic. Allow the problem to converge to a reasonable level. Restart the problem with Finite Rate Chemistry or Finite Rate Chemistry/Eddy Dissipation Model using the results from the previous problem as an initial guess. Restarting the flamelet model from EDM does not work well because of the different model approach. This is because a previous EDM run would not provide mixture fraction mean and variance fields. Instead, it would be better to reduce the timestep for a few iterations. Combustion introduces a strong coupling between scalars, energy and momentum. In difficult problems, you may find it helps to calculate a cold flow solution before turning on combustion. In general for the Finite Rate Chemistry Model, the time scale of the combustion process is smaller, so you may have to continue with a smaller timestep to force the mass fraction and energy equations to converge. The time scale for the Eddy Dissipation Model is equal to the turbulence time scale (k/e). In some cases, it may be appropriate to use a larger time scale for the mass fraction equations. This is particularly true when there are regions of small flow velocity in the domain. In these cases, the time needed to convect the components into all areas of the domain may be relatively large. |
4楼2012-11-28 16:49:32
