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Old   November 5, 1999, 12:56
Default FLUENT capability ?
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One part of my thesis is to do some engine simulation job using different tubulent model(K-e, LES) and study their results influenced by grid qualities. I like to use Fluent5.0 on it. But I donot have any experiences about it, especially the LES model. Could you tell me if Fluent can do this kind of job ? How about its capability (K-e, LES model) on this particular complex simulation (3d, unsteady or steady, moving valve or stationary )? How expensive is the grid if I use LES model ?

Thanks in advance and look forward to some reply.

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Old   November 7, 1999, 13:33
Default Re: FLUENT capability ?
John Chien
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(1). The turbulence modeling and its impact on the CFD solution is an onging research issue. It is an advanced subject. By selecting option-A, or option-B, is not going to tell you why the results are different, or which way to go next. (2). The effect due to the mesh quality is always an issue for any CFD run, and the standard approach is to carry out the mesh independent solution process. (3). When these two issues are applied to the complex IC engine flow field, it becomes a real difficult problem. (4). To be able to say something about the computed engine flow field, one needs to have reliable set of test data first. Otherwise, it is difficult to address the accuracy of the results besed on two different models. (5). AS for the mesh quality, one needs to start with the test data flow filed. The flow field variations will determine the quality of the mesh required, that is the mesh arrangement and the mesh density distribution. (6). My suggestion is: try to study the flow field data of IC engine in details, about the flow directions, the gradients, the turbulence intensity (TKE) distribution, etc. Then create a strategy about the layout and the distribution of the mesh. That is try to put high mesh density in the area where the flow gradient is high. This will give you the needed information for the mesh independent solution. The same is true for the turbulence models. Whether the flow field is accelerating, decelerating, turning, mixing or separating, will tell you which model is more appropriate for that particular region. It is hard to find a turbulence model which will cover all different flow conditions. Therefore, simply by selecting model-A or -B is not going to answer the questions in this research field. (7). But, if you say you like to learn how to use a commercial CFD code, then it is a different story. (8). The basic issue in this case is: your understanding about the detail flow field in the IC engine. It determine which area to use what turbulence model on what mesh arrangement. Because we know that different turbulence models and mesh arrangement will give different results. That is a fact. But if you are trying to validate the commercial code, it is a good idea to check with the vendor of the code to see whether they have already done something similar. This will save you a lot of time.
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