Horizontal Axis Tidal Current Turbine: Numerical and Experimental Investigations

Marine current energy is one of the most interesting renewable and clean energy resources that have been less exploited respect to wind energy. Only in Europe this type of energy is available for 75 millions of KiloWatts and in terms of exploitable energy the amount is about 50 milliards of KiloWattHour. In the last years, the realization of horizontal axis turbine for the exploitation of the tidal currents is having, to world-wide level, a considerable increment. Many are the societies and the consortia that have decided to invest in such type of energetic source. The present paper provides a summary of the work done at the Department of Aeronautical Engineering (DPA) of the University of Naples “Federico II” regarding the numerical and experimental investigations of a scaled model of an horizontal axis hydro turbines designed to harness energy from marine tidal currents. The horizontal axis hydro turbine has been designed and analyzed using numerical codes available at DPA. Among these codes, some were already available at DPA and were based on standard Glauert’s blade element theory, modified following Prandtl’s theory and the “Higher Order Correction” method, while a new unsteady code, based on vortex lifting line theory, has been developed and now is under validation. The wind turbine has been designed to work at a specific Tip Speed Ratio (TSR) and particular effort has been put in order to avoid the cavitation on the blade surface. The blades are composed by airfoils with decreasing thickness from root to tip to accommodate both structural and aerodynamic needs. Airfoil design and selection are based on: E appropriate design Reynolds number; E airfoil thickness, according to the amount of centrifugal stiffening and desired blade rigidity; E roughness insensitivity, most important for stall regulated wind turbines; E low drag, not as important for small wind turbines because of passive over speed control and smaller relative influence of drag on performance; E high-lift root airfoil to minimize inboard solidity and enhanced starting torque.