Wind Energy

196 B. Hillmer et al.
c f
0.010
0.008
0.006
0.004
0.002
0.000 0.0 0.1 0.2
x / l
0.3
Ma = 0.15, Re = 6.6, clean
FLOWer
Ma = 0.15, Re = 6.6, c = 0.25,
FLOWer, Hansen
Ma = 0.15, Re = 6.6, c = 0.50,
FLOWer, Hansen
Ma = 0.15, Re = 6.6, c = 1.00,
FLOWer, Hansen
Ma = 0.15, Re = 6.6, bump,
h = 0.4mm, FLOWer
Ma = 0.15, Re = 6.6, bump,
h = 0.6mm, FLOWer
Ma = 0.15, Re = 6.6, bump,
h = 1.0mm, FLOWer
Fig. 35.5. Measured and simulated friction coefficients cf (suction side) against
axial distance over chord x/c at an angle of attack α =6 ◦
The k-ω-model is not able to predict cmax l . The comparison with another
turbulence model in future is reasonable. The calculated drag values are
considerably below measured values. This is probably due to experimental
conditions.
The discrete roughness created with an obstacle as part of the airfoil
contour indicates a correct trend with a decreasing lift/drag ratio against
the obstacle height. However, the calculated lift/drag ratios are considerably
too large. The effect on the transition location is small. The discrete roughness
represented by an additional turbulence source does not have a significant
effect.
References
1. Rooij R.P.J.O.M. van, Timmer W.A. (2003) Roughness considerations for thick
rotor blade airfoils, Journal of Solar Energy Engineering 125:468–478
2. Timmer W.A., Rooij R.P.J.O.M. van (2003) Summary of the delft university
wind turbine dedicated airfoils, AIAA-2003-0352:11–21
3. Timmer W.A., Schaffarczyk A.P. (2004) The effect of roughness on the performance
of a 30% thick wind turbine airfoil at high Reynolds numbers, Wind
Energy 7(4):295–307
4. Freudenreich K., Kaiser K., Schaffarczyk A.P., Winkler H., Stahl B. (2004)
Reynolds number and rougness effects on thick airfoils for wind turbines, Wind
Engineering, 28(5):529–546
5. Krumbein A. (2002) Coupling the DLR Navier–Stokes Solver FLOWer with an
eN-Database Method for laminar-turbulent Transition Prediction on Airoils,