DESIGN OPTIMISATION OF SAVONIUS WIND TURBINE OPERATING AT LOW SPEEDS USING CFDFOR WIND FARM APPLICATION

Abstract

The low wind speed condition in Malaysia poses a great challenge for generation of useful energy via wind turbine applications. Even though the Savonius wind turbine is proven to be able to operate well at low wind speed conditions, the low power efficiency has hindered its potential of commercialisation. This research investigated the feasibility of generating power at wind speeds of below 6 mis using a commercial computational fluid dynamics (CFD) solver. A standalone Savonius wind turbine was optimised by considering its blade twist angle, overlap ratio, and end plates design. The numerical methodology was validated first against the published wind turbine data. Optimum numerical parameters were obtained via a sensitivity study. The turbine performance was measured based on the ratio of power predicted by the simulation to the theoretical power available. The standalone helical Savonius turbine with 90° twist achieved up to 0.128 of power efficiency about 45% higher than conventional S-shape Savonius turbine. To further increase the turbine power efficiency, the effects of multiple turbines in several configurations were also studied. CFD results show that a proper location of the downstream turbine can enhance the overall power generation. Factors such as the gap distance and turbine direction of rotation were evaluated. Several cases of oblique two-turbine, oblique three-turbine and cluster turbine were analysed. At this stage, the effect of the turbine gap distance and rotational coupling on turbine performance were observed. Positive flow interaction between turbines at 0. 5-Diameter and I-Diameter gap distance enhanced the co-rotating turbine performance by 10% and 5% respectively. Furthermore, the application of contra­rotating downstream turbine shows better performance when placed on returning blade region of the upstream turbine. The turbine power efficiency improved by 2% at ]­Diameter gap distance for oblique three turbines. The optimum oblique layout was used to design triangular cluster configuration of three turbines. The overall performance improved up to 9%. Thus, the oblique and cluster turbine configuration were extended to a wind farm layout comprising nine turbines in V-formation. The implementation of contra-rotating turbine in wind farm layout resulted power efficiency enhancement up 11 %. The flow interaction between the neighbouring turbine contributes into an improvement of driving torque on each turbine in the system, hence improved the overall turbine performance. As far as the wind farm performance is concerned, the wind power density of the V-formation yielded four to five times higher than nine isolated turbines. Therefore, the placement of the multiple wind turbines in an optimised V-formation layout is the best choice in terms of space utilisation in limited wind farm area and its overall power enhancement.