The present work deals with the assessment of variable fidelity simulation models to analyze the complex phenomenology of a turbine operating in a tidal stream. In the framework of an Unsteady Loading Tidal Turbine Benchmarking Study by Supergen ORE HUB [Tucker Harvey et al.(2021)], performances of an Horizontal Axis Tidal Turbine (HATT) are extensively analised. A general purpose finite volume solver based on the solution of the unsteady Navier-Stokes equations for multi-block structured grids is considered [Dubbioso et al.(2019), Gregori et al.(2020)]. The turbine has been simulated over a wide range of tip-speed ratios, by means of unsteady RANS simulations, in the frame of reference fixed to the rotating turbine, in uniform onset flow and calm water conditions. Since the work is also focused on the assessment of design-oriented hydrodynamics models, crossvalidation studies between URANS and BIEM (Boundary Integral Equation Model) results are presented. The wake-field by URANS is presented and analised with the aim to validate results by lower fidelity models. The wake-field has been processed and geometrical parameters of the trailing wake geometry were derived, allowing, in principle, the improvement of simplified wake models as those adopted by the BIEM.