A numerical technique has been developed for efficiently simulating fully three-dimensional viscous fluid flow around horizontal axis wind turbines. In this approach the viscous region surrounding the blades is modelled using the 3D unsteady Navier–Stokes equations. The inviscid region away from the boundary layer and the wake is modelled using potential flow. The concentrated vortices that emanate from the blade tip are treated as piecewise straight line segments that are allowed to deform and convect at the local flow velocity. The Biot–Savart law is used to estimate the velocity field associated with these vortices. Calculations are presented under axial wind conditions for the NREL Phase VI rotor, a two-bladed rotor tested at the NASA Ames Research Center 80 ft × 120 ft wind tunnel. Good agreement with the measurements is found. The computations were verified against the experimental data and then used to develop improved engineering models for the loss of lift at the blade tip and for the delay in the stall angle at inboard locations. The procedure of developing improved aerodynamics models using validated CFD results as a guide is presented. The improved models are incorporated in a blade element momentum analysis to study the post-stall behaviour of a three-bladed rotor tested at NREL for further validation. Copyright © 2002 John Wiley & Sons, Ltd.