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Yes, it changes. I put all information in the excel file, enclosed here
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This looks strange. Is "wall_dist" the first cell distance in "m"? Is this exported from Fluent or from your meshing tool?
I am asking because, did you write down the OMG_vis formula without wall units? It's OMG_vis = 6 * nu / (0.072 y^2) So for constant y (in m) you should have a constant omega wall value... |
Yes, "wall_dist" is the adjcent cell to the wall in "m" and it is exported from Fluent.
The OMG_vis formula is based on y+ not y and y+ is a nondimensional parameter. Moreover, Omega depents on wall shear, too; so that it has not constant value along the plate. The main problem is that what formula Fluent uses for the Omega value of the wall. Quote:
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You will get OMG_vis = 6 * nu / (0.072 y^2) No y+, no wall shear. |
Yes, you are right. Then, how is Fluent calculate the omega of the wall?
Actually, the same formula is written in Fluent theory guide, Quote:
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Are you 100% sure about the grid? Is the wall distance really constant?
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Yes, I am sure, because my case study is a flat plate and I use hexahedral elements (structural mesh) and cells have the same wall distance.
I enclosed two figures of the mesh Quote:
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I remember when I checked these values for one of my cases everything was alright. There must be some mistake in the data. Can you upload the whole fluent case?
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Yes, sure, you can find the cas and data file in the Dropbox, linked here:
https://www.dropbox.com/sh/rg87mkr95...MyjuKLP-a?dl=0 Quote:
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Ali, you should try to understand my post #14 in this thread (very first post of me). I think you can not plot omega on the surface, because Fluent doesn't let you. You are currently plotting interpolated values. Try this: plot "k" along the plate. You will see, that it isn't zero everywhere. This doesn't make sense, because k-boundary condition is zero. This can only be explained by interpolation errors during post-processing.
I also found in the userguide: In ANSYS FLUENT you can choose to display the computed cell-center values or values that have been interpolated to the nodes. By default, the Node Values option is turned on, and the interpolated values are displayed. For line contours or profiles, node values are always used. If you are displaying filled contours or profiles and you prefer to display the cell values, turn the Node Values option off. Filled contours/profiles of node values will show a smooth gradation of color, while filled contours/profiles of cell values may show sharp changes in color from one cell to the next. For face-only functions (e.g., Wall Shear Stress), the cell values that are displayed for boundary zone surfaces will actually be the face values. This is only true in the case of boundary zone surfaces created for postprocessing, where the actual cell values are used for the part of the surface which lies in the interior. These face values are more accurate, as face-only functions are computed on the faces and not on the cells. |
Hi!
I don't understand this: Quote:
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yPlus value is calculated for each cell next to the wall, each cell has it's y+ value, that's why you have min/max and avg values.
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I know..
But they are not in the supposed interval, that's because I posted that |
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Infinite thanks, Roman! :)
If I use the same wall functions of the motorbike tutorial (nutKwallfunction, kqRwallfunction and omegawallfunction) and standard k omega model what values of y+ I should have? And for standard k epsilon with epsilonwallfunction? |
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More information on wall functions and near wall behavior can be found in 1. Wilcox, D. C. (2006). Turbulence modeling for CFD (3rd ed.). La Canada Calif.: DCW Industries. 2. Pope, S. B. (2000). Turbulent flows. Cambridge [u.a.]: Cambridge Univ. Press. 3. Schlichting, H., & Gersten, K. (2000). Boundary Layer Theory (8th Revise). Darmstadt: Springer Berlin Heidelberg. 4. Bredberg, J. (2000). On the Wall Boundary Condition for Turbulence Models. Göteborg, Sweden. (gives explanation of wall functions in OpenFOAM) 5. Schiestel, R. (2008). Modeling and Simulation of Turbulent Flows. London, UK: ISTE. http://doi.org/10.1002/9780470610848 |
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It's the first time I hear about y+ values below 0.2 leading to wrong results. Do you have more information about this? Best regards, Kate |
Helllo,
So by having all in hand, now in modelling high-speed flow with K-w sst, if your first grid is in Y+=150 (log layer). and you are interested in studying the vorticity of separated flow downstream of a backstep (Backward Facing Step), does this putting first grid point on log layer make any problem? :confused: what is the difference between Fluent and OpenFoam in this? Can anyone introduce me some papers in this regard? Thanks |
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