Variation of the incidence with the NACA 012 profile

Introduction

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

The data of the simulation are the following :
- Minfinite= 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 lift coefficient is calculated with the help,of this figure.

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.