For this project, two additional blade profiles were identified as being potential candidates for tidal current turbine applications and tested against the baseline turbine for an identical rotor geometry. These were the NACA 63-418 and NACA 63-424 aerofoils. The above graph shows the NACA 63-418 exhibiting better performance over the majority of the inflow velocities in comparison to the baseline model. However, the baseline model performs better at speeds above 3.5 m/s. The NACA 63-424 exhibits better performance at speeds below 2.6 m/s and reduced performance at mid-high range speeds.
In comparison to the baseline model, the NACA 63-418 achieved a 4.4% increase in energy recovery over one year of operation, whilst the NACA 63-424 achieved a 1.1% increase. This is largely due to the fact that within our tidal model, any turbine design analysed has a limited rated power of 210 kW. This is achieved for each case around 2.6 m/s. As observed in the power curves, both profiles tested against the baseline case exhibit better performance below this speed. Any power generated above this speed will be limited to 210 kW for each design; therefore, these speeds are less influential within the comparison.
It was expected that the NACA 63-418 would exhibit the optimum performance as it is the thinnest profile we analysed, having the best lift to drag ratio. However, this aerofoil may have more structural implications in comparison to the other two profiles if employed at the root of a tidal current turbine blade. Thicker aerofoils may need to be employed to withstand the high forces within this region. This is one of the main reasons we added the functionality to model multiple profiles along the span of the blade. For future applications, a range of thick and thin aerofoils can be modelled on the same blade to depict a more realistic situation where performance may have to be sacrificed in order to maintain structural integrity.
