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Old   November 26, 2010, 06:35
Default area on reference value
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when i scale airfoil geometry on the scale factor from 1 to 0,0823 should i change the value of area to 0,0823 m^2 on the reference value to get appropriate cl an cd??
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Old   November 26, 2010, 08:36
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is it 2d or 3d?
if 2d, 0,0823 is ok, but if 3d, you must square it.
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Old   November 27, 2010, 04:54
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it is 2d airfoil
but i still confused about pressure coefficient CP
why it's always same altough i've scale the geometry??
(same velocity and AoA)
i use inviscid model
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Old   November 27, 2010, 06:33
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cp is a dimensionless value and is related with geometry(airfoil). if you dont change your geometry, cp will be same. this is due to inviscid flow. and since Cl and Cd are integrals of Cp, they will not change, either.

BUT:
In real life, the flow is viscous and cp slightly changes with velocity (Reynolds number). This is because laminar and turbulent flow characteristics over the surface.

You should study boudary layer, laminar-turbulent seperation to understand what I mean.
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Old   November 28, 2010, 08:03
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i've scale airfoil geometry from 1 m to 0,083 m, cp result doesn't change but cl & cd change
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Old   November 28, 2010, 08:09
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cl and cd are x and y components of cp.
do you confuse center of pressure with coefficient of pressure?
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Old   December 9, 2010, 04:35
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here we are.
i following this tutorial (https://confluence.cornell.edu/displ...ecificationand) then i try for different velocity also i scale the geometry from 1m to 0,0823m
but the xyplot on pressure coefficient always same for the same AoA why altough i change the velocity..
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Old   December 9, 2010, 05:36
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because you are using inviscid model. use laminar or turbulent models.
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Old   December 10, 2010, 03:12
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inviscid = viscosity is negliable (myu=0)
cp= (p-pfs)/0,5.rho.v^2

there is no myu on the cp formula..
so why it's because of the inviscid model??
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