CFD Investigation of Torque Generation in an Archimedes Screw Hydrokinetic Turbine

ABSTRACT: The Archimedes Screw hydrokinetic turbine (AST) is a promising technology for renewable energy generation in shallow, low-velocity, and bidirectional flows, but the mechanisms governing its torque production remain poorly understood. This study uses computational fluid dynamics (CFD) to investigate the performance and torque-generation mechanism of a three-flight AST inclined at 30° and operating in two configurations previously examined experimentally. Transient simulations were performed in ANSYS Fluent using a sliding mesh and flow-induced rotation approach within an unsteady Reynolds-averaged Navier–Stokes framework with the SST k–ω turbulence model. The results show that pressure forces dominate torque generation, while viscous contributions are comparatively small. Importantly, this behaviour is observed at a relatively low Reynolds number of approximately 4.5 × 10⁴, indicating that Reynolds-number dependence becomes weak at Reynolds numbers substantially lower than those expected in practical deployments. For the first configuration, with the upstream edge of the turbine at the free surface, the CFD model predicted a maximum power coefficient of 0.85 at a tip speed ratio of 1.50, compared with an experimental value of 0.40 at 0.53. For the second configuration, with the downstream edge of the turbine at the free surface, the corresponding maximum power coefficient was 0.82 at a tip speed ratio of 1.51, compared with 0.34 at 0.54, as experimentally observed. The simulations also captured strong cyclic torque variations; the maximum variation in torque was over three times the mean value for both configurations. Comparison of the cavitation and pressure coefficients indicates little likelihood of cavitation at the experimental flow velocity but suggests possible cavitation onset at higher velocities.