The influence of coning a wind turbine rotor is analysed numerically using the blade element momentum (BEM) method and an actuator disc model combined with the Navier–Stokes equations. The two models are compared and shortcomings of the BEM model are discussed. As a first case, an actuator disc with a constant normal loading of CT = 0·89 is considered. In accordance with theoretical predictions and investigations by Madsen and Rasmussen (European Wind Energy Conference, Nice, 1999; 138–141), the computations demonstrate that the power coefficient based on the projected area of the actuator disc is invariant to coning. The induced velocities, however, are no longer constant, but vary as a function of spanwise position. Next, the flow past the 2 MW Tjæreborg wind turbine is computed with and without coning. The most important findings from this study are that, although the power is reduced when the rotor is coned, the power coefficient based on the projected area is only slightly changed. The computations show that upstream coning results in a 2%–3% point higher power production than the corresponding downstream coning of the rotor. The Navier–Stokes computations show that the integrated loading, i.e. the root shear force, is higher than the one predicted by the BEM method, which is reduced approximately in proportion to the projected area. Copyright © 2001 John Wiley & Sons, Ltd.
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