The Bolund Project

The Bolund experiment is a field campaign that provides a new dataset for validating models of flow in complex terrain. It has been the basis for a unique blind comparison of flow models. An increasing number of wind farms are being installed in complex terrain where wind resources are good, but the wind shear and turbulence can exceed the design basis. CFD is becoming a standard tool to quantify such wind conditions and determine the optimum positions of the wind turbines. However, these flow models have usually only been validated against wind tunnel experiments with simple terrain forms.

Characterisation of the Unsteady Flow in the Nacelle Region of a Modern Wind Turbine

A 3D Navier-Stokes solver has been used to investigate the flow in the nacelle region of a wind turbine where anemometers are typically placed to measure the flow speed and the turbine yaw angle. A 500 kW turbine was modelled with rotor and nacelle geometry in order to capture the complex separated flow in the blade root region of the rotor. A number of steady state and
unsteady simulations were carried out for wind speeds ranging from 6 m/s to 16 m/s as well as two yaw and tilt angles. The flow in the nacelle region was found to be highly unsteady, dominated by unsteady vortex shedding from the cylindrical part of the blades which interacted with the root vortices from each blade, generating high velocity gradients. As a consequence, the nacelle wind speed and the nacelle flow angle were found to vary significantly with height above the nacelle surface. The nacelle anemometry showed significant dependence on both yaw and tilt angles with yaw errors of up to 10◦ when operating in a tilted inflow.