[en] This paper presents the development of a vortex lattice based aerodynamic calculation for wind turbine blades. Emphasis is placed on the modeling of flow separation using the vortex lattice approach. This modeling is carried out by shedding a second free wake at the leading edge, which travels downstream at the local air velocity. The decision on whether to shed a wake or not is taken by looking at the sectional lift characteristics of the blade’s airfoil. If the local angle of attack exceeds the maximum lift angle, then a leading edge wake element is shed. Results from the method are presented for both attached and separated flow and compared with predictions obtained from the Blade Element Momentum theory. It is shown that the shedding of the leading edge wake can increased significantly the agreement between vortex lattice and Blade Element results in cases where there are significant regions of separated flow. This improvement concerns mostly forces acting normal to the rotor plane; tangential forces depend more strongly on the drag and neither method calculates a full representation of the drag.