# aspect ratio in a domain

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 September 9, 2011, 07:41 aspect ratio in a domain #1 New Member   Rakesh Join Date: May 2011 Posts: 21 Rep Power: 8 Dear ALL! Please clarify ,in case of variable meshing in a domain, what can be maximum acceptable aspect ratio ?what are other parameters to assess mesh quality in this case? regards,

 October 26, 2011, 11:32 #2 Member   jonathan Join Date: Jun 2009 Posts: 47 Rep Power: 11 I actually was discussing this with an ANSYS rep this past week and here are some target values to hit: The max aspect ratio is dependent on the precision of the solver: Single precision - max aspect ratio : 1000 or so Double precision - max aspect ratio : 5000 - 10,000 Another metric to watch out for is expansion ratio - or the change in volume of adjacent cells. In my opinion I would try to keep the expansion ratio less than 20% Finally the skewness angle is another important metric to watch. This measures essentially the orthogonality of the adjacent faces of a single cell. This metric is repersented differently depending on the mesher or solver calculating the value so you will need to consult the documentation for the software. Essentially you want two faces of a cell to be orthogonal (the angle between faces should be around 90 degrees) but this is typically very difficult to achieve for all cells in a mesh and the angle between adjacent faces can easily fall to much lower values. Try to keep the minimum skewness angle between faces larger than about 15 deg. Again take note of how the mesher /solver calculates skewness and if in doubt contact a rep for that software for more clarification. Hope this helps and happy meshing!! It's always the hardest part of performing a CFD calculation and will give you many grey hairs over your career!!!

 October 26, 2011, 13:47 #3 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,358 Blog Entries: 6 Rep Power: 45 These values are good enough for the two equation eddy viscosity models. Requirements are much tighter for the Reynolds stress models ( should be less than 100)

 October 26, 2011, 16:26 #4 Member   jonathan Join Date: Jun 2009 Posts: 47 Rep Power: 11 Yeah that's a good point, I'm sure the mesh quality requirements can be different depending on the types of turbulence models used.

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