first mesh hight must be higher or boundry layer??

mshf7 · August 23, 2013, 13:46

hi
I am modeling a ship hull.when I am meshing and using boundry layer around the hull, the amount of total thickness of boundry layer must be more or the hight of first tetra mesh which I use?I mean the total thickness of boundry layer hight should fill first mesh hight or reverse vica?
thank you so much

brunoc · August 23, 2013, 17:46

From what I understand from your question, you're asking if the total boundary layer element height should be equal to tetra sizes. If that is the question, then generally, no.

You should calculate the height of the first element according to the y+ required by your turbulence model. Then choose an appropriate growth rate (will vary between 1.05 and 1.3, you might need to do a sensitivity analysis here) and last, choose a number of layers such that the volume ratio between the last BL element and the first tetra is around 0.7 - 0.9.

That means in most cases the total height from the elements in your BL will be 2-5 times the local tetra size.

mshf7 · August 24, 2013, 08:19

thank you dear brunoc
you got my question right.there is a problem when I obey these rules and meshing, the aspect retio would increase very much and some warnings appearance.also I cannot decrease the tetra size so much in orther to be 2-5 times lower than B.L element.
thank you

August 23, 2013, 13:46	first mesh hight must be higher or boundry layer??	#1
mshf7 New Member mohammad Join Date: May 2013 Posts: 10 Rep Power: 12	hi I am modeling a ship hull.when I am meshing and using boundry layer around the hull, the amount of total thickness of boundry layer must be more or the hight of first tetra mesh which I use?I mean the total thickness of boundry layer hight should fill first mesh hight or reverse vica? thank you so much

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August 23, 2013, 17:46		#2
brunoc Senior Member Bruno Join Date: Mar 2009 Location: Brazil Posts: 277 Rep Power: 21	From what I understand from your question, you're asking if the total boundary layer element height should be equal to tetra sizes. If that is the question, then generally, no. You should calculate the height of the first element according to the y+ required by your turbulence model. Then choose an appropriate growth rate (will vary between 1.05 and 1.3, you might need to do a sensitivity analysis here) and last, choose a number of layers such that the volume ratio between the last BL element and the first tetra is around 0.7 - 0.9. That means in most cases the total height from the elements in your BL will be 2-5 times the local tetra size.

August 24, 2013, 08:19	hi	#3
mshf7 New Member mohammad Join Date: May 2013 Posts: 10 Rep Power: 12	thank you dear brunoc you got my question right.there is a problem when I obey these rules and meshing, the aspect retio would increase very much and some warnings appearance.also I cannot decrease the tetra size so much in orther to be 2-5 times lower than B.L element. thank you