The installation of wind turbines in urban sites requires consideration of the wind characteristics affecting the energy production (turbulence, environment roughness due to the surrounding buildings …), the self-starting capability and the type, hence the performance, of the wind turbine. In this paper, a three-dimensional CFD analysis of an aerodynamic Savonius wind turbine is performed under steady wind conditions. The inclusion of a deflector was also investigated, and the performance compared to the initial design. Results of the 3D analysis showed that an optimized axisymmetric deflector improves the power coefficient in all wind directions and over the entire operating range of the turbine. The deflector also increased the average starting torque by 30%, thus extending the operating range of the turbine with respect to the wind speed. •Design of a new deflector type with a simple axisymmetric shape to improve the intrinsic capacities of a Savonius wind turbine.•Numerical optimization of the concentrator.•3D dynamic modeling of the concentrator and the wind turbine.•Profits and highlighting of the obtained results compared to existing deflectors/concentrators.