The effect of the blade number on a cross-flow hydrokinetic turbine

Abstract

The effect of the blade number of a cross-flow hydrokinetic turbine is studied in this paper. To begin with, a blade cross-sectional shape NACA0025 is selected, as was used in a previous study. Secondly, after the turbine blade is modeled, the simulation cases are conducted numerically by use of a commercial package program, ANSYS Fluent. Before further analysis is conducted, validation is executed to make sure the calculation is reliable. The result shows that the blade number has effect on the turbine's efficiency or power coefficient (Cp). A 2-bladed, 3-bladed and 4-bladed turbine can obtain Cp values of 37.5%, 33.6% and 30.2%, respectively. Additionally, from the component torque yields gained by upper and lower surface of a blade respectively, it is revealed that the lower surface obtains much more torques than upper surface does during rotational range from 20° to 180°. Also, during this rotational range, the 2-bladed turbine proved to be more efficient than the other two cases. In contrast, the upper surface gained more torque yields than lower surface during rotational interval from 180° to 380°(=20°). And during this rotational interval, the torque yields obtained by the upper surface offset the lower surface torque yields, which made the total torque yields seem insignificant. The reduction of the blade number is thought to be the cause of efficiency enhancement due to less complex flow condition caused by the interaction of the blades upon rotation.