A mathematical model for fluid dynamics wind turbine design (based on the blade element momentum theory) has been implemented and improved. The mathematical simulations have been compared with experimental data found in the literature. The simulation was performed for the whole wind velocity range, in on-design and off-design conditions. Several simulations were performed in order to maximize the agreement between the simulated and experimental data. Particular attention was paid to the tangential induction factor and to the models for the representation of the lift and drag coefficients. A comparison was also made between the mathematical model presented in the paper and those considered in the literature. Finally, the model was implemented to optimize rotor performance, especially at low wind velocities, which is crucial to produce power during the machine start-up phase. (c) 2007 Elsevier Ltd. All rights reserved.