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2014-08-28 15:24
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foam_Umagnitude_probe_along_lines.png (13,208 bytes) |
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2014-08-28 17:10
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theoretical_Umagnitude.png (16,165 bytes) |
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HI, Reading the code it is clear that for z>Href, you get U=Uref, but this model doesn’t agree with the atmospheric boundary layer references I have seen. In all of them it is suggested to use the logarithmic profile from bottom to top, in the inlet, and I think the users will normally expect this behavior. I suggest that the developers change this model to avoid confusion. Best Regards, Paulo |
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I agree; I see no physical justification for U=Uref when z>Href. Do you have access to the reference cited in the .H file: D.M. Hargreaves and N.G. Wright, "On the use of the k-epsilon model in commercial CFD software to model the neutral atmospheric boundary layer", Journal of Wind Engineering and Industrial Aerodynamics 95(2007), pp 355-369. If so is there any mention of U=Uref when z>Href? My plan is to simply remove this adjustment unless anyone can provide a reason to keep it in which case I could make it an option. |
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Hi Henry, I found about five papers that discuss boundary conditions for wind simulations, the Hargreaves paper is one them. I checked the paper again and no mention is made of a constant velocity layer in the upper region. I think that if some user needs this constant velocity region he could provide this using a separate patch in this region. It wouldn’t be difficult to do that. Thanks for your attention. Happy new year. Paulo |
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Thanks for getting back to me on the paper. I am not sure why a limiter on U was applied and see no physical justification for it. Further, I found no corresponding limit applied to the associated epsilon BC and this inconsistency if further cause for concern. Based on this I have removed the limit on U and rewritten the expressions in standard OpenFOAM field algebra form. Please let us know if there are any further problems with this BC. Resolved by commit 8df3ba9ae1136eb60afa244d5e6e6ab07b2339b7 |
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Hi Paulo, As you have the references to hand could you look up and let me know how a consistent turbulent kinetic energy distribution is defined for this profile? I think it would be convenient if in addition to atmBoundaryLayerInletEpsilon a atmBoundaryLayerInletK BC is provided and I would be happy to write it. Thanks. |
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Quick heads up - This issue is somewhat related to this bug report: http://www.openfoam.org/mantisbt/view.php?id=860 |
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Dear All, Thank you very much for your answers. I agree with the points you developed. I think removing the limit U = Uref when z > Href is a good idea because as you said there is no physical justification in the literature. So how can we download the updated atmBoundaryLayerInletVelocity BC ? Moreover , I believe to know that a logarithmic wind profile is generally considered valid for the 10 % of ABL (so from 0 to 100m approximately ) but I do not see any distinction for atmBoundaryLayerInletVelocity between below 100 m and above 100m. It is like if the log wind profile is valid for any height. Maybe someone knows what kind of profile we can apply above 100 m and implement this in the atmBoundaryLayerInletVelocity. It could be useful for simulations which imply skyscrapers and large domain. |
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You can get the latest OpenFOAM-2.3.x from the git repository: http://www.openfoam.org/download/git.php https://github.com/OpenFOAM/OpenFOAM-2.3.x I am just testing an updated atmBoundaryLayerInletVelocity with corrected documentation and will push shortly. What profile would you like above 100m? If you can provide a specification for the velocity, turbulence intensity and dissiation rate it should be straight forward to implement. |
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Hi Henry, The inlet condition used for the turbulent kinetic energy k is a uniform value equal to (U^*)^2/sqrt(cmu) where U^* is the friction velocity and cmu is the constant of the k-epsilon model that usually is used with the value 0.09. It's not difficult calculate this value and edit the ABLConditions file but if you could provide a function for this would be nice. Best regards, Paulo |
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I have rationalized the ABL BCs and added the corresponding k BC by commit 10ee5c477b96a5957291303df5807c46091bab90 in https://github.com/OpenFOAM/OpenFOAM-dev |
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Thank you for the work. I'm new in the process of using a modified boundary conditions or solver files in OF with github. Can someone please explain me the procedure ( in details) to implement the new boundary conditions in my OF without waiting the new version of OF ? Thank you ! Gaspacho |
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http://www.openfoam.org/download/git.php |
- Anonymous
