Study on Aerodynamic Characteristics of a Savonius Wind Turbine with a Modified Blade

Abstract

In order to improve the static start-up problem of Savonius wind turbines, a Savonius wind turbine with a modified blade is proposed. It was obtained by twisting the half-cylindrical blades of the basic Savonius wind turbine by 70°. The aerodynamic performance of the wind turbine before and after the modification was compared. Firstly, the static torque coefficient of two wind turbines at different azimuth angles were obtained by means of three-dimensional numerical simulation. The static flow field around the wind turbine was analyzed. Then, the output power and speed characteristics of a spiral Savonius wind turbine under different incoming wind speeds were evaluated in the wind tunnel. The results show that, compared with the Savonius wind turbine with half-cylindrical blades, the spiral wind turbine could start at any azimuths in one rotation cycle. The reverse torque was eliminated. The static torque coefficient fluctuation range was reduced by 10%. The start-up performance was effectively improved. This investigation could provide guidance for the improvement of start-up characteristics of Savonius wind turbines.

Start-up Dynamics of Vertical Axis Wind Turbines: A Review

“…Ushiyama [28] carried out numerical investigations on the start-up and steady performance of several drag-based rotor configurations. It has been reported that as the rotor's aspect ratio increases, the rotor reaches its steady performance earlier, which is in-line with the observations of Mu et al [27]. Evaluating the effects of overlap ratio, it has been reported that increase in overlap is reflected in slightly higher steady operational speed of the rotor.…”

“…Start-up failure was recorded at AoAs of 70° and 150°, providing insights into the dead band range of AoAs. Similar to the dead band range of AoAs observed by Mu et al [27], the initial acceleration of the rotor is shortly followed by deceleration until a slight reverse rotation is noticed. The rotor demonstrates repetition of both these stages in the dead band range, showing a sinusoidal pattern in the rotational speed of the rotor.…”

“…It has been further reported that due to no generator load on the VAWT, the average torque output from the VAWT was zero. Mu et al [27] investigated the effects of modifying a two-bladed drag-based rotor by twisting the blades 70° to create a spiral turbine, as shown in Figure 3(c). The investigation also considered a traditional drag-based rotor as the baseline model (similar to the one shown in Figure 3(a)), which failed to self-start at AoA between 120° and 170°, whereas the spiral rotor self-started at AoAs between 0° and 180° subject to windspeeds between 6m/s and 12m/s.…”

“…Figure 3. Different lift-based rotor designs (a) Conventional rotor[29], Two-stage rotor[30], (c) Spiral rotor[27] …”

Examination of the Effect of Triangular Plate on the Performances of Reverse Rotating Dual Savonius Wind Turbines

“…The comparison of the percentage increase in the improved power coefficient obtained with this study with other studies in the literature is given in Table 1. It is possible to classify the literature studies on this subject as additional designs made outside of [26] and structural designs made inside of Savonius wind turbines [27,28]. Here, additional guide design studies made in front of or around the turbine without any modifications to the conventional Savonius wind turbines with two semi-circular blades were evaluated.…”