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

mohammad · May 3, 2011, 03:41

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

mohammad · May 9, 2011, 03:27

Please...help me ...TNX

sail · May 9, 2011, 08:37

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, 11:03

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

mohammad · May 9, 2011, 11:25

Quote:

Originally Posted by sail

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

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,
Thanks for your answers.
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, 11:30

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, 12:36

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.

mohammad · May 16, 2011, 10:28

Quote:

Originally Posted by sail

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, 13:21

Quote:

Originally Posted by mohammad

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.

May 3, 2011, 03:41	How to know the know the Boundary Layer thickness and the edge velocity on a 3D wing?	#1
mohammad Senior Member mohammad Join Date: Dec 2010 Location: UK Posts: 246 Rep Power: 17	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

May 9, 2011, 03:27		#2
mohammad Senior Member mohammad Join Date: Dec 2010 Location: UK Posts: 246 Rep Power: 17	Please...help me ...TNX

May 9, 2011, 08:37		#3
sail Senior Member Vieri Abolaffio Join Date: Jul 2010 Location: Always on the move. Posts: 308 Rep Power: 17	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

May 9, 2011, 11:03		#4
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	you will also need a very fine mesh at the surface to get an accurate measurement of the leading edge boundary layer thickness.

May 9, 2011, 11:30		#6
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	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

May 9, 2011, 12:36		#7
sail Senior Member Vieri Abolaffio Join Date: Jul 2010 Location: Always on the move. Posts: 308 Rep Power: 17	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.