Water turbines with a brimmed diffuser by using wind lens technology

A diffuser-type structure that is capable of collecting and accelerating the approaching wind and water flow has been developed. Namely, we have devised a diffuser shroud with a brim that is able to increase the approaching flow speed substantially by utilizing various flow characteristics, e.g., the generation of low-pressure region by vortex formation, flow entrainment by vortices, and so on, of the inner or peripheral flows of a diffuser shroud equipped with a brim. As a result, the shrouded wind turbines equipped with a brimmed diffuser (called wind-lens turbine, WLT) demonstrated power augmentation for a given turbine diameter and wind speed by a factor of about 2-5 compared to a standard wind turbine. The mechanism of the wind-lens technology can also be applied to the water flow. Water-lens turbine (WaLT) demonstrated 2.5-times power enhancement using a similar diffuser design used in a compact wind-lens turbine. In this research, we show some experimental and numerical results, focusing on a water turbine using wind-lens technology immersed into a water tank with a finite width and depth. Due to the effects of free surface and Venturi-shaped side walls, the maximum power coefficient Cw reaches 2.21 based on the rotor swept area, indicating 6-times increase compared to that for a conventional water turbine in an open flow. © 2021 by Begell House, Inc.