Wind Energy

41 3D-CFD-Simulation of a Wind Turbine Rotor Focusing the Hub Area 229
Fig. 41.2. Upper figure: Photography of flow separation effects on EU 56 rotor
blade, Lower figure: 3-D Simulation: Surface streamlines on suction side
separated flow can be pointed out by comparing the radial velocity field on the
left side to the absolute velocity field on the right side. This is representative
for all near-hub-profiles that are affected by flow separation.
Fig. 41.3. 3D Simulation, Velocity and Vector field for r = 3.75 m, left figure: Radial
velocity component, right figure: Velocity field
The evaluation of the airflow at different profiles along the rotor blade show
an expanding and intensifying radial flow with growing rotor-radii. Beginning
at the hub, radial velocities accelerate and remain at 13 m s −1 until the rotor
ratio of r/R = 28%, where they start to decelerate. At r/R = 30% all radial
flows have been redirected to the trailing edge (see Fig. 41.4).
In Fig. 41.2 the air flow separates at cylindric root profiles characteristically.
Two eddies in lee develop differently with growing radius. The analysis
of this velocity distribution and those for larger radii indicate a helical movement
of the vortex centers.