Nozzle and Diffuser in Drifting Horizontal Turbine Flow.

Based on the characteristics of Kuroshio passing through Green Island, Taiwan, a new type of floating platform has been designed to capture the maximal power of the marine current. The inclusion of nozzle and diffuser in a shrouded duct is frequently used to accelerate, decelerate, or affect flows in a desirable manner. In this study, a shrouded nozzle-diffuser horizontal turbine was designed by Kirke, B, (2005). Matsushima, T et al.(2005). Five geometric parameters are determined to have an optimal power take off (PTO) from the ocean current. The Harmony search technique was used to search for the best combination of the geometric parameters. The parameters needed to be determined are inlet and outlet diameters, the lengths of the nozzle and diffuser and the gap between blade tips and the inner wall of the duct. Ohya, Y et al.(2010). The simulation of the characteristics of flow passing the system and the calculation of the PTO are made by Fluent. The proposed nozzle-diffuser duct and the meshes arrangement and simulated velocity vectors arc illustrated in Fig. 1. The simulated results show the proper nozzle-diffuser design can effectively increase the power take off (PTO) and PTO coefficient can be as large as 0.48 which is beyond the reported average values. [ABSTRACT FROM AUTHOR]