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12.11 Grid Considerations for Turbulent Flow Simulations

Successful computations of turbulent flows require some consideration during the mesh generation. Since turbulence (through the spatially-varying effective viscosity) plays a dominant role in the transport of mean momentum and other parameters, you must ascertain that turbulence quantities in complex turbulent flows are properly resolved if high accuracy is required. Due to the strong interaction of the mean flow and turbulence, the numerical results for turbulent flows tend to be more susceptible to grid dependency than those for laminar flows.

It is therefore recommended that you resolve, with sufficiently fine meshes, the regions where the mean flow changes rapidly and there are shear layers with a large mean rate of strain.

You can check the near-wall mesh by displaying or plotting the values of $y^+$, $y^*$, and ${\rm Re}_y$, which are all available in the postprocessing panels. It should be remembered that $y^+$, $y^*$, and Re $_y$ are not fixed, geometrical quantities. They are all solution-dependent. For example, when you double the mesh (thereby halving the wall distance), the new $y^+$ does not necessarily become half of the $y^+$ for the original mesh.

For the mesh in the near-wall region, different strategies must be used depending on which near-wall option you are using. In Sections  12.11.1 and 12.11.1 are general guidelines for the near-wall mesh.

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