Gas turbines operate under highly demanding thermal and aerodynamic conditions, particularly in the high-pressure turbine stages where the gas temperature can be significantly greater than the melting point of the components. Turbine vanes use modern cooling systems that include internal air passages and multi-row film cooling to protect the surface from severe heat loads. In this context, the current thesis investigates the aero-thermal behaviour of a high-pressure turbine vane through numerical analysis. To assess the reliability of the selected Computational Fluid Dynamics (CFD) approaches in predicting the flow field and heat-transfer processes in a cooled vane, this work focuses on both modelling boundary layer development and the identification of the most appropriate parameters to be used for performance evaluation.