Experimental and Numerical Studies on Savonius Rotor for Hydropower Utilization

Abstract

Hydrokinetic technologies harvest renewable power by harnessing the kinetic energy of water from free-flowing rivers, streams, dam head/tailrace, and irrigation channels. Savonius rotor is one of the simple and low-cost vertical drag type devices used for the extraction of hydrokinetic power. In the present study, various experimental and numerical investigations were carried out to enhance the performance of the Savonius hydrokinetic turbine. Initially, the effect of bed slope on the performance of the modified Savonius turbine were carried out experimentally. An in-house fabricated scale-down model of the Savonius rotor is tested in a multipurpose tilting flume at 0°, 0.5°, 1.0°, 1.5 and 2.0° channel inclination to determine performance under controlled conditions. It is observed that at the tip speed ratio of 0.92 and channel inclination of 0.5° compared to 0° inclination, the CP and CT improved to 40% and 10%, respectively. It is found that the torque and power developed by the turbine are maximum at a bed slope of 2.0°, owing to the maximum available energy. Further, the effect of taper on conventional Savonius turbine is studied numerically with zero bed slope, aspect ratio, and inlet velocity of 1.0 and 0.5 m/s. The results show a 5% increase in the performance of a conventional turbine compared to the tapered turbine with a taper angle of 5 and zero bed slope. In order to enhance the performance of the turbine blade by reducing the negative torque developed by the returning blade profile, the semi-circular blade profile is reformed into a modified V-shaped blade profile. The experimental and numerical investigation is carried out in a multipurpose tilting water flume using V-shaped rotor blade profiles by maintaining a fixed V-angle of 90o, varying length of V-edges, arc radius, with a constant aspect ratio of 0.7, without taper and zero bed slope at an inlet water velocity of 0.3090 m/s. From the experimental and numerical results, it was found that, the optimum blade profile (V4) has developed a CPmax of 0.22 and 0.21 respectively, at a tip speed ratio of 0.87. It was found that the CPmax of the optimal V- shaped blade profile (V4) is 19.3% higher than the semi-circular blade profile. Further, the effect of overlap ratio ranging from 0.0-0.3 using optimum rotor blade (V4) were studied numerically. The results reveal that the turbine's performance with a zero overlap ratio is higher than the turbine blade with an overlap ratio ranging from 0.05 to 0.3. The rotor blade V4 is further investigated by varying the V-angle ranging from 90 to 40 numerically. The results show that, for 80 V-angle rotor blade, the CPmax was found to be 0.23 at a tip speed ratio of 0.9. This rotor blade is used for experimental analysis to study the effect of aspect ratio ranging from 0.7 to 1.75 using top, middle, and bottom plates with an inlet velocity of 0.513 m/s. The rotor blade with two endplates and one mid-plate with an aspect ratio of 1.75 has shown a significant increase of performance by 86.13% at a tip speed ratio of 0.86 compared to the turbine blade with two endplates. It is recommended to have two endplates and one mid-plate for the turbine blade with an aspect ratio of 1.75 for better performance. The outcome of the parametric studies carried out in the present research work establishes a key technical basis for enhancing the efficiency of hydrokinetic power generation.