Wind Energy

228 J. Rauch et al.
41.2 Method
The unity of rotor and nacelle was designed as shown in Fig. 41.1. Since effects
from the tower are not investigated in this phase of the study it was not
implemented within the geometry. As a consequence the 120 ◦ symmetry of
the three bladed rotor and nacelle could be used. This is a common attempt
in turbo machinery simulation and reduces the calculating effort significantly.
Hub, nacelle and blade design are based on a Winwind WWD-1 turbine.
Fig. 41.1. Section of the volume mesh
The upper surface of the domain is designed as an opening boundary
condition to allow the typical expansion of the stream tube around the WT.
Within the flow regime the rotor has a 100 m distance upwind and 450 m
downwind till the boundaries of the domain, its radius is 100 m. A higher
mesh quality was achieved by using three general grid interfaces (GGI) that
permit a high grid resolution in the hub area with an reasonable amount of
grid elements. The numerical simulation was performed using the Reynolds
Averaged Navier–Stokes Equation (RANS) with the standard k–ε model.
41.3 Results
On this basis the aerodynamic power was derived from the pressure field
on the rotor blade surface and agrees well with technical specification and
measurements. The resulting flow separation area along the blade shows good
agreement with observations of the manufacturer. Since k–ε models tend to
underestimate flow separation [3], the calculated separated area is smaller
than found in reality, which is shown in Fig. 41.4. Through this simulation
several effects were observed. Here two of them are described.
The two velocity distributions in Fig. 41.3 both rely on the same velocity
scalefrom0to30ms −1 . The domination of radial flow components in the