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Old   July 13, 2006, 05:46
Default measuring boudary layer
  #1
Cyril
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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 !
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Old   July 14, 2006, 07:48
Default Re: measuring boudary layer
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Steve Silvester
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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
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Old   July 15, 2006, 01:15
Default Re: measuring boudary layer
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Razvan
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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
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Old   July 17, 2006, 02:07
Default Re: measuring boudary layer
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Cyril
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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 ... ?
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Old   July 17, 2006, 05:26
Default Re: measuring boudary layer
  #5
Ralf Schmidt
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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!
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Old   July 18, 2006, 04:06
Default Re: measuring boudary layer
  #6
Cyril
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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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