Flow characteristics of the wake of a horizontal axis tidal current turbine are studied by numerically solving Reynolds-averaged Navier-Stokes (RANS) equations. The rotational effects of the three-bladed turbine is modelled with both the Moving Reference Frame (MRF) and the sliding mesh techniques. By comparing the numerical results with theoretical and experimental data, it is found that the sliding mesh technique can more accurately predict the hydrodynamic loads from current and the wake than the MRF technique. Moreover, an alternative turbine modelling technique, Actuator Disk Model (ADM), is also utilised and its results agree well with the sliding mesh results in the far wake velocity if the turbulence length scale (TL) used in the simulation is about half the hub radius and the input porous properties are derived from power coefficient of the turbine. Finally, turbine to turbine interactions have been numerically investigated using the sliding mesh technique.