Performance characteristics of the Archimedes screw hydrokinetic turbine

The Archimedes Screw hydrokinetic turbine (AST) is garnering considerable interest because of its potential applicability in harvesting river and tidal energy. The turbine is well suited to bi-directional flows, low-velocity flows, and shallow watercourses. Because the AST is a reasonably new hydro-technology, very little literature is available on its design and performance optimization. This study experimentally investigates the torque and power generation of the AST. Laboratory scale turbine models with one, two, and three flights (blades) were tested in a water tunnel to measure torque and angular velocity at different flow velocities and varying inclination angles ($\beta$) of the turbine. A maximum coefficient of performance ($C_P$) of 0.41 was obtained at a tip speed ratio ($\lambda$) of 0.52 at a flow velocity ($U_{\infty }$) of 0.45 m/s and $\beta$ = 30${}^{\circ }$ for a turbine with two flights. In the case of the 3-flight turbine, the highest value of $C_P$ was also obtained at 30${}^{\circ }$ (0.40 at $\lambda$ = 0.53). For the 1-flight turbine, a maximum $C_P$ of 0.23 was obtained at a $\beta$ of 28${}^{\circ }$ and $\lambda$ of 0.30. The results also showed a time-varying fluctuation in the torque, which reduced in magnitude with an increase in number of flights. The ripple was found to occur once-per-revolution and not once-per-flight, irrespective of the number of flights.