CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

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

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 24, 2015, 02:00
Red face
  #1
Member
 
N B Khan
Join Date: Jan 2014
Posts: 39
Rep Power: 7
bestniaz is on a distinguished road
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 plate..is 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 meshing..so that i can mesh it according to requuirement of Y+


Quote:
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!
Quote:
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
bestniaz is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[snappyHexMesh] No layers in a small gap bobburnquist OpenFOAM Meshing & Mesh Conversion 6 August 26, 2015 09:38
Validity & transformation of boundary layer equations Obad Main CFD Forum 2 April 27, 2015 02:59
[ICEM] set up of boundary layer for cylinder Attique ANSYS Meshing & Geometry 13 June 5, 2014 00:55
Boundary Layer roughness/ low reynolds wall treatment Luigi_ STAR-CCM+ 1 March 14, 2012 08:40
Formula for velocity in buffer layer of turbulent boundary layer nickvinn Main CFD Forum 0 February 3, 2012 11:57


All times are GMT -4. The time now is 20:17.