*Introduction*

The aim of this part is the study the
*decrochage
*of the NACA 012 airfoil.

The data of the simulation are the
following :

- M*infinite*=
0.85

- incidence
i : 0 degree to 40 degrees

- the used
grid is the coarse one

10 simulations were computed and we
expose two situations :

- incidence=0

- incidence=5

- incidence=16

The 16 incidence corresponds to the
experimental *decrochage* of the airfoil.

*Presentation
of tthree cases*

Profil with no incidence
:

We can see 5 degrees of incidence.

We notice that there is an uppper
velocity on the top of the airfoil and a little stop point in front of
the airfoil.

Now, we can observe 16 degrees of incidence.

There is still the stop point in front
of the airfoil and the upper velocity on the top.

But, we can observe a very low velocity
behind the airfoil.

The lift of the airfoil is due to this
velocity difference betweem the bottom and the top of the airfoil. Since
the velocity is higher on the top of the airfoil, the pressure is lower
which leads to the lift (the airfoil is *aspire* in the top).

The lift is studied in the following
part.

*Study of the
lift*

After the simulation of each case,
a fortran program was used in order to see the portance with XMGR.

XMGR gives us the lift coefficient
on the profil with the lenght on the abscisse and the lift on the ordonate.

The graphs shows 3 different portance
:

- AVBP : the
lift we computed with AVBP

- theorical
: the formula is Cp=2*pi*sin(alpha) till the *decrochage*

- experimental
: it is trivial !!!!!!

The first graph gives the 3 lift untill
20 degrees.

We wonder that Theorical and Experimental
portance are always identical. It is a normal situation before the *decrochage.*

If we are interested in the AVBP lift,
we notice that it is always upper than the other but have got he same *pente.*
* *But the 3 lifts are nearly
identical between 13 and 17 degree.

The second graph shows the evolution
of the lift after 20 degrees for AVBP and Theorical.

We wonder that there is no *decrochage
*with
AVBP, only a lift decreasing.