[求助]如何得到壁面处网格的y＋值

alicefhy

本人刚刚接触fluent，不是很熟悉，望能指点一下

cresfo

在solution xy plot里面选择turbulence ,在其相应的菜单中选择wall Yplus
即可，当然那个面的还得您自己选择！

夜行人

谢谢楼主

alicefhy

谢谢cresfo

alicefhy

出口和入口边的网格是按同样的比例画的，保证壁面处网格有足够的密度

cresfo

我很奇怪，进出口需要看y+吗？又没有壁面！

alicefhy

我说图怎么看着这么诡异，原来是因为进出口没有壁面啊，我以为出口与壁面相交的那个点就是壁面呢

alicefhy

应该是这个 吧，该怎么分析这个图？
网格都是gambit画的，fluent里没有自适应网格

cresfo

看你用的什么模型，不同的模型对于y+的要求是不同的，
Wall Functions

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The log-law, which is valid for equilibrium boundary layers and fully developed flows, provides upper and lower bounds on the acceptable distance between the cell centroid and the wall for wall-adjacent cells. The distance is usually measured in the wall unit,  ( ), or . Note that  and  have comparable values when the first cell is placed in the log-layer.
For standard or non-equilibrium wall functions, each wall-adjacent cell';s centroid should be located within the log-law layer, . A  value close to the lower bound ( ) is most desirable.
Although FLUENT employs the linear (laminar) law when , using an excessively fine mesh near the walls should be avoided, because the wall functions cease to be valid in the viscous sublayer.
As much as possible, the mesh should be made either coarse or fine enough to prevent the wall-adjacent cells from being placed in the buffer layer ( ).
The upper bound of the log-layer depends on, among others, pressure gradients and Reynolds number. As the Reynolds number increases, the upper bound tends to also increase.  values that are too large are not desirable, because the wake component becomes substantially large above the log-layer.
Using excessive stretching in the direction normal to the wall should be avoided.
It is important to have at least a few cells inside the boundary layer.

Enhanced Wall Treatment

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Although the enhanced wall treatment is designed to extend the validity of near-wall modeling beyond the viscous sublayer, it is still recommended that you construct a mesh that will fully resolve the viscosity-affected near-wall region. In such a case, the two-layer component of the enhanced wall treatment will be dominant and the following mesh requirements are recommended (note that, here, the mesh requirements are in terms of , not ):
When the enhanced wall treatment is employed with the intention of resolving the laminar sublayer,  at the wall-adjacent cell should be on the order of . However, a higher  is acceptable as long as it is well inside the viscous sublayer (  to 5).
You should have at least 10 cells within the viscosity-affected near-wall region ( ) to be able to resolve the mean velocity and turbulent quantities in that region.

Spalart-Allmaras Model

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The Spalart-Allmaras model in its complete implementation is a low-Reynolds-number model. This means that it is designed to be used with meshes that properly resolve the viscous-affected region, and damping functions have been built into the model in order to properly attenuate the turbulent viscosity in the viscous sublayer. Therefore, to obtain the full benefit of the Spalart-Allmaras model, the near-wall mesh spacing should be as described in Section  12.11.1 for the enhanced wall treatment.
However, as discussed in Section  12.3.7, the boundary conditions for the Spalart-Allmaras model have been implemented so that the model will work on coarser meshes, such as would be appropriate for the wall function approach. If you are using a coarse mesh, you should follow the guidelines described in Section  12.11.1.
In summary, for best results with the Spalart-Allmaras model, you should use either a very fine near-wall mesh spacing (on the order of ) or a mesh spacing such that .

-  Models

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Both -  models available in FLUENT are available as low-Reynolds-number models as well as high-Reynolds-number models. If the Transitional Flows option is enabled in the Viscous Model panel, low-Reynolds-number variants will be used, and, in that case, mesh guidelines should be the same as for the enhanced wall treatment. However, if this option is not active, then the mesh guidelines should be the same as for the wall functions.

Large Eddy Simulation

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For the LES implementation in FLUENT, the wall boundary conditions have been implemented using a law-of-the-wall approach as described in Section  12.9.4. This means that there are no computational restrictions on the near-wall mesh spacing. However, for best results, it might be necessary to use a very fine near-wall mesh spacing (on the order of ).

alicefhy

谢谢～～