The hydrodynamics of a three bladed horizontal axis turbine is investigated. The performance of a turbine of 0.7 m of diameter and its wake were obtained from experiments and numerical simulations. A six components load cells is used for thrust and hydrodynamic power measurements, and Laser Doppler Velocimetry technics for wake characterisation. A three-dimensional software, taking into account the non stationary evolution of the wake generated by turbine blades is developed. The flow is discretised with particles carrying vorticity, which are advected in a Lagrangian frame. Both numerical and experimental power coefficient Cp and velocity maps were compared. Experiments and numerical data showed a satisfactory agreement in term of the shape of the wake and of Cp, whereas the turbine was only modelled as a rotor composed of three blades. The results showed that the maximum decay of the wake velocity deficit is obtained in the near wake and the extension of velocity deficit until 10 D downstream. These studies highlight the problems that can appear during the configuration of turbines in a farm. The main aim of this work is to understand how the wake decays downstream, in order to estimate the effects produced in the lee side of turbines and more generally on its close environment.