Influence of Extension Ratio on the Performance of the Modified Savonius Hydrokinetic Turbine

In the present investigation, a modified Savonius hydrokinetic turbine of 0.245 m turbine diameter (D), 0.1 overlap ratio, 0.2 shape factor, and 0.002 m blade thickness (t) has been investigated numerically to study the influence of extension ratio on the performance of the turbine. The effect of vane end extension on the performance of the Savonius hydrokinetic turbine is investigated by numerical simulations. Two-dimensional transient simulations are done with a pressure-based solver by keeping the diameter of the turbine constant. The study is carried out in a finite-volume solver by using unsteady Reynolds Navier-Stokes equations with a k-omega shear stress transport turbulence model. The coefficient of torque is considered for the 12th revolution of the turbine for different extension ratios of 0, 0.041, 0.082, 0.122, 0.163, and 0.204. The maximum instantaneous coefficient of torque (Ct) is obtained for vane orientations of 100 degrees to 130 degrees and 280 degrees to 310 degrees. The maximum coefficient of power (Cp) of the turbine is 0.2441 for an extension ratio of 0.041, which is 15.5% higher than that of the turbine with a zero-extension ratio.