Performance analysis of vertical axis water turbines under single-phase water and two-phase open channel flow conditions

Abstract

We conduct performance analyses of a family of vertical axis water turbines (VAWTs) under single-phase water and two-phase open channel flow conditions using unsteady Reynolds-averaged Navier-Stokes (URANS) numerical simulations. The performance, including self-starting capability and energy harvesting efficiency, of a recently developed hybrid Darrieus-Modified-Savonius (HDMS) design is examined under single-phase water flow conditions. With a two-way coupled fluid-structure interaction (FSI) approach, we demonstrate that the water turbine has excellent self-starting capability. After that, the effects of the Reynolds number, tip speed ratio (TSR), and geometric design of the turbine, including turbine size, solidity, and number of blades, are systematically studied. Since the main function of the modified Savonius rotor is to assist self-start, and this part has a negligible effect on energy harvesting performance when the turbine is under stable operation, only the Darrieus rotor is studied under two-phase open channel flow conditions to save computational cost. A key finding is that larger blockage ratios result in better energy harvesting performance of the water turbines. When the blockage ratio is 60% and the TSR of the turbine is 5.0, the power coefficient of the water turbine can reach up to 73%, which exceeds Betz's limit.