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-   -   How to know the know the Boundary Layer thickness and the edge velocity on a 3D wing? (http://www.cfd-online.com/Forums/main/87923-how-know-know-boundary-layer-thickness-edge-velocity-3d-wing.html)

How to know the know the Boundary Layer thickness and the edge velocity on a 3D wing?

Hi guys,
My questions are simple...Using CFD ( especially CFX)...
1-How to know the Boundary Layer thickness and the edge velocity on a 3D wing( blade)?...
2- Think that I have determined the BL thickness everywhere on the blade surface....Then how to save the geometry[ x,y,z=(thickness)] of the BL on the whole wing in a Text file or Excel file?

Regards

 sail May 9, 2011 07:37

to get the bl thickness you can create an isosurface of veocity = 99% free stream velocity. then the distanche between the isosurface and the wing is your thickness

 mettler May 9, 2011 10:03

you will also need a very fine mesh at the surface to get an accurate measurement of the leading edge boundary layer thickness.

Quote:
 Originally Posted by sail (Post 306790) to get the bl thickness you can create an isosurface of veocity = 99% free stream velocity. then the distanche between the isosurface and the wing is your thickness
Quote:
 Originally Posted by mettler (Post 306814) you will also need a very fine mesh at the surface to get an accurate measurement of the leading edge boundary layer thickness.
Dear Andrew, dear Sail,
one other question : if I want to plot the velocity profile inside the BL , I must use some other isodurfaces between wall( zero velocity) to 0.99V and then plot the velocity profiles inside the BL, isn't it?

Regards

 mettler May 9, 2011 10:30

what you would do in Fluent is create a plane perpendicular to surface, and then plot the velocity in that plane. You can do it as a contour plot. Or, you can get the values at each grid from the plane and determine the thickness from there. That is why you need a fine grid towards the surface. That is how I would do it. But, setting a criteria for .99V would be the fastest

 sail May 9, 2011 11:36

to get the bl Vprofile, if you need the plot for the whole section you can simply create a plane and then plot the velocity contours on it, as mettler said.

else, if you need the profile at vairous chord coordinates, make a line normal to the foil surface at each station you need to investigate and just plot the velocities on those lines.

Quote:
 Originally Posted by sail (Post 306790) to get the bl thickness you can create an isosurface of veocity = 99% free stream velocity. then the distanche between the isosurface and the wing is your thickness
Hi everybody,
A new question arises; when the blade is rotary( in Wind turbine) which speed should i work with when i want to calculate 0.99V? with Local( roartion+ axial for any radial station) ,with Average speed ( at mid-radial station) or just with axial wind speed?

 f-w May 16, 2011 12:21

Quote:
 Originally Posted by mohammad (Post 307793) Hi everybody, A new question arises; when the blade is rotary( in Wind turbine) which speed should i work with when i want to calculate 0.99V? with Local( roartion+ axial for any radial station) ,with Average speed ( at mid-radial station) or just with axial wind speed?
Use the rotational+axial velocity as reference for rotary surfaces.

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