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Any formula for approximating the boundary layer thickness around a cylinder?

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Old   October 24, 2015, 02:00
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Dear I am doing flow around cylinder.
How to calculate the Boundary layer in case of flow around cylinder. The above formula is for flat there any formula for flow around cylinder...

I know one option is that after getting solution, we can find boundary layer thickness from vel profile,,, but i am interested in to find BL before that i can mesh it according to requuirement of Y+

Originally Posted by Appleologe View Post
Hey Lazaros,

thx for reply again.

Now I understand....., not all, but the bigger part of the topic!

I have found this formula too:

Its the Formula to calculate, where you have 99% from your mean velocity U, in normal direction from your wall. But its for a flat plate, today I download the book from Schlichting to get more information about this.

Yes, I made a super fine Layer with HM (0.00005mm, growth rate 1,2 and 3 Layers).
It works and I made a run with AcuSolve. It works with the SST-Model, but dont converge.

The k-omega Model has with the same Mesh problems. I have suddenly areas where i get a lot of kinetic energy!? Then the energy appears and jump in a other Area of the fluid.

Now I go drink a beer because I have birthday today!

THX and I give feedback again!
Originally Posted by Captain Crossflow View Post
What kind of geometry are you considering? An airfoil?
What exactly do you need the boundary layer thickness for? Visualization?

For just visualizing the boundary layer for the flow around an airfoil you could use the total pressure, which is constant in the free stream and decreases inside the boundary layer.

I only know of a 'direct' formula for calculating the boundary layer thickness for flat plate flow. For general flows you have to find the boundary layer edge by applying an appropriate criterion, e.g. reaching 99% of the velocity of the free stream.
However, the boundary layer thickness as a representative value can be quite inaccurate because of the small velocity gradients at the boundary layer edge. Applying 99% or 99.5% as edge criterion can already result in a quite large difference. Integral boundary layer values (displacement thickness / momentum loss thickness) are in my opinion a better choice.

Last edited by wyldckat; October 24, 2015 at 11:01. Reason: Moved posts from old threads to an independent thread. Left quotes for reference
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