# Some more realistic OpenFOAM runs

As a first test, I am trying to reproduce the graphs of coefficient of lift $$C_l$$ and coefficient of drag $$C_d$$ as functions of angle of attack $$\alpha$$ from http://airfoiltools.com/airfoil/details?airfoil=naca2408-il. The airfoil is 1m long, the airspeed is 10m/s, and the kinematic viscosity $$\nu$$ is 1E-5 for a Reynolds number of 1E6. $$C_l$$ and $$C_d$$ are measured for $$\alpha = \{-5,0,5,10,15,20\}$$. I am unclear on the reference length and area in $$C_l$$ and $$C_d$$, but that will be obvious as a constant factor between the graphs.

On the recommendation of a friend (I do not want to get stuck down any rabbit holes) these use the SST k-omega turbulence model. The constants for incoming turbulence intensity are taken from: k-Omega-SST-DES-Report. At high angles of attack the airfoil sheds vortices:

And the plot of $$C_l$$ and $$C_d$$ vs $$\alpha$$:

Error bars are given from the standard deviation of the forces. The vortex shedding causes periodic changes in each coefficient. I am bothered that $$C_l$$ doesn’t turn over at $$\alpha\approx 15^{\circ}$$ as for the airfoil tools database, and am now trying to figure out what causes the difference.

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## 2 thoughts on “Some more realistic OpenFOAM runs”

1. Garth Whelan says:

That’s child’s play. I’ve surfed the web for 22 hours in a row now.