The Oscillating Water Column system (OWC) is an interesting concept for ocean wave energy extraction. Several kinds of air turbines have been used for pneumatic energy conversion to mechanical energy. The Wells turbine has been used widely in OWC plants. However, as an alternative the self-rectifying turbine called Impulse turbine has been studied during the last years. We are interested in the radial version of the Impulse turbine, which was initially proposed by McCormick. A former research work aimed to improve the knowledge of the local flow behaviour and the prediction of the performances for this kind of turbine has been carried out using CFD (FLUENT®). The objectives of that work were connected mainly to the elaboration of a suitable 3D model for air flow simulation in a radial Impulse turbine. Model validation was conducted through a comparison with available experimental results. In the present, the objective is, using the numerical model, to develop a new radial impulse turbine geometry that gets better performances than the original one. This new turbine geometry will be exploited next in a project for an OWC of 250 kW. In this paper we describe the flow behaviour and the performances of this new turbine. For that, we study the Torque and Input coefficients, the losses and flow direction in the turbine elements.