# measuring boudary layer

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 July 13, 2006, 05:46 measuring boudary layer #1 Cyril Guest   Posts: n/a I'm simulating a small experimental rocket (3D/Euler) with a small angle of attack. I would like to measure the size of the boundary layer but I don't know how! (It very important beacuse if it's too high, the wings are unusefull !!) Thanks !

 July 14, 2006, 07:48 Re: measuring boudary layer #2 Steve Silvester Guest   Posts: n/a Hi, Try plotting your velocity data on a line normal to the surface (create this line in the surfaces menu) and identify the point where you get free stream velocity (where the curve flattens out) - should be a good indication of your boundary layer height at that point. Regards Steve

 July 15, 2006, 01:15 Re: measuring boudary layer #3 Razvan Guest   Posts: n/a I am sorry to interrupt, but there is no boundary layer to measure in an Euler simulation, no viscosity => no boundary layer!!! More, if the angle of attack is small, then there are no recirculations in the wing area, so that's it! Do a viscous (Navier-Stokes) simulation if you want to see any boundary layer at all. Best for all, Razvan

 July 17, 2006, 02:07 Re: measuring boudary layer #4 Cyril Guest   Posts: n/a Thanks for your answers ! You're right, there's no boundary layer in an Euler Case... I mande a mistake in my question... ! What I want to measure is the size of the turbulences due to an angle of attack, to see how much wing surface is under turbulences (=unsusefull) : http://img89.imageshack.us/img89/9683/sanstitreeh7.jpg Maybe I can try to plot "turbulence" or speed on a normal surface ... ?

 July 17, 2006, 05:26 Re: measuring boudary layer #5 Ralf Schmidt Guest   Posts: n/a Hi! One way to measure the BL is following: Create an iso-surface with surface of constant velocity magnitude (or axial vel, whatever is better). The iso-valus should be 99% (or 99,5% or 99,9%...) of the free stream vel. Now, to plot, use solution xy-plot: Deselect "position on x-axis" and select for y-axis function: grid, y-coordinate and for x-axis function: grid, x-coordinate. Now select the iso-surface, that you created in the first step and plot! Thats it!!! Hope, it helps!

 July 18, 2006, 04:06 Re: measuring boudary layer #6 Cyril Guest   Posts: n/a Thanks, but if I wants to see the speed profile at the rear of my fuselage (I don't know what speed to put in the iso) how should I do ?? I'm in 3D symetric (X-Y sym plane, Y perpendicular to my fuselage : http://img92.imageshack.us/img92/7622/tubeuo7.png). I tryed to create an iso "x", and plot it, baut nothing appears on the graph...

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