Computational fluid dynamics (CFD) gives a unique insight into the complex flow phenomena that govern the aerodynamics of wind turbines. Through a dedicated research and development effort CFD is steadily reaching a level of maturity where it is becoming indispensable in the analysis of modern wind turbine designs. This article gives an insight into recent developments in wind turbine flow simulations in the Wind Energy Department at Risø National Laboratory, where recent additions to our CFD code have made it possible to model the entire turbine including rotor, tower, nacelle and ground boundary. Here, an investigation carried out into the interaction between the rotor and the tower on a downwind turbine will be presented.