KR518: The R12 documentation (Section 10.3.2) states 'The LES turbulence model cannot be used with the mixing plane model'. However, in Appendix A. (fluent model compatibility table) it shows that LES is compatible with mixing plane. Please clarify.

Compatibility chart corrected such that "n" appears for LES + mixing plane. The Fix is in R13 and 12.1 errata

Clarification: In general LES is not compatible with mixing-plane model. They are two conflicting models. One resolve features as in LES while the other mix-out or average flow features as in mixing- plane. However, in both Fluent and CFX there is nothing preventing the user from running LES and mixing-plane model. This is not an oversight. There is a reason for that. So the Documentation is correct in stating that they are not compatible but we could also indicate that we allow for these two models to be turned on and coexist together.

The reason for that is there are certain modeling tricks we can perform where we will use LES while mixing-plane is active in multi-stage simulation. For example, we can have a 3 stage compressor. Our interest is mainly in the last stage. So we want to resolve flow features and account for unsteady flow interaction between the last two blade rows. We can model the last stage with sliding interface while the other stages are modeled via mixing-plane or MRF. The LES is needed for better modeling of flow in the last stage what is taking place near the mixing-plan region as far as LES concern is not important, but the front stages will provide better flow initialization than modeling this configuration without the front stages.

So the confusion here is that we have stated in our documentation that LES is not valid which is true, but when someone go to turn LES on while mixing-plane is used we do not prevent them from doing so. The reason for that is mainly due to some modeling trick that we can play to help us cut computational costs.

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