Performance analysis of spherical-shaped Darrieus hydrokinetic turbine for an in-pipe hydropower system

The present study aimed to explore the applicability of Darrius hydrokinetic turbine (HKT) curbed inside a closed conduit, i.e., in-pipe hydropower system. Six numbers of 3-and 4-bladed Spherically shaped Darrieus HKTs (SDHKT) were designed having various diameters. Numerical analysis was performed in ANSYS CFX to calculate performance parameters, viz. coefficient of power (CP) and coefficient of torque (Ct), to get an idea of possible power production. Numerical analysis was conducted by varying fluid flow from 0.5 to 2.0 m/s with an increment of 0.5 m/s. Blockage ratios (BR) were maintained as 0.705, 0.796, and 0.893 for an 0.080 m (nominal) diameter pipe. The results were validated with experiments at 1.0 +/- 0.2 m/s flow velocity. It was found that CP increased with the blockage ratio. In general, the performance of the 4-bladed SDHKT was found better than the 3-bladed SDHKT. However, the performance of 3-and 4-bladed SDHKTs at a BR of 0.796 were considered for further analysis due to operational constraints. It was observed that overall CP increased with fluid velocity but with less proportionate. Pressure drops across the turbine increased with increased TSR and fluid flow velocities inside the pipe.