Numerical modelling of a dual-rotor marine current turbine in a rectilinear tidal flow

In this study, numerical simulation is used to investigate a counter-rotating dual-rotor marine current turbine (MCT) that is aligned for a rectilinear tidal current. Results of power and thrust coefficients and the mean axial velocity in the wake are compared with that of the blade element momentum (BEM) method coupled with the Park wake model. For a single-rotor MCT, small discrepancies are observed for front rotor, and larger discrepancies for rear rotor when comparing the CFD and BEM results. The mean axial velocity in the wake agrees better with the higher turbulence intensity (TI). CFD results shows that the power coefficient (C-p) of rear rotor depends on the ambient turbulence intensity. The maximum C-p of dual-rotor turbine is 5% higher than that of just the front rotor. Streamlines show that a large vortex is formed behind the rear rotor. The numerical simulations give more credibility to the BEM Park model, but also points to its sensitivity to the incoming turbulence intensity.