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.

Author: Garth Whelan

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2 thoughts on “Some more realistic OpenFOAM runs”

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