# compute bondary layer thickness

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 May 30, 2006, 03:56 compute bondary layer thickness #1 Ralf Schmidt Guest   Posts: n/a Hi! How to compute the thickness of the boundary layer?? Ok, it is the distance to the wall, where the vel. is 99% of the outer vel. It is possible to create a iso-surface for that value... But what I want is a xy-plot (or a profile) on my surface of the B-L thickness. Any Idea? Ralf

 May 30, 2006, 04:28 Re: compute bondary layer thickness #2 Steve Silvester Guest   Posts: n/a Hi, You could do an iso-clip on a plane normal to the surface using clip values of 99% max velocity and a min a tiny fraction lower. That'll create a surface restricted to your boundary layer thickness which you can then use to create an xy plot on plotting thickness (whatever your co-ordinate normal to the surface is) against position. That does it, I'm fairly sure theres a few ways to go about this though. Regards Steve

 May 31, 2006, 07:35 Re: compute bondary layer thickness #3 Ralf Schmidt Guest   Posts: n/a Thank you, I've got it working now... BUT maybe one can help my with another Problem: What free stream vel. should I use for computation? I simulate a very simple case: turbulent flow over a plate (2D, incompressible calculation (air)) - pressure outlet BC at the top of my domain and at the right side, and a - vel. inlet BC at the left side (the plate is at the bottom). Now (because of displacement due to the B-L. ) the vel. above the plate increases to a value about 5% higher than the inlet vel. What value should I take as free stream vel.??? The top side of the domain has a distance of about 35 times the BL-thickness from the plate. Is that distance to small?? Or are the BC wrong? Any idea? Ralf