Literature Review LITERATURE REVIEW AND BASIC THEORY

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CHAPTER II LITERATURE REVIEW AND BASIC THEORY

2.1. Literature Review

There are some researches dealing with increasing of Savoniuswind turbine performance. Altan et al Altan, Atılgan et al. 2008 conducted a study to introduce a new curtaining arrangement to improve the performance of Savonius rotors. The curtain arrangement was placed in front of the rotor preventing the negative torque opposite the rotor rotation. The maximum power coefficient of the Savonius wind rotor is increased to about 38.5 with the optimum curtain arrangement. Mahmoud et al Mahmoud, El-Haroun et al. 2012 carried out an experimental study to determine the most effective operation parameters on different geometries of Savonius wind turbine such as number of blades, stages, overlap ratio, aspect ratio and existence of end plates. The research found that the two blades rotor is more efficient than three and four ones. Double stage rotors have higher performance. The rotors without overl ap ratio β have better performance. The end plates give higher efficiency. And the power coefficient increases accordingly with the aspect ratio ra ise α. Wong et al Wong, Chong et al. 2014 conducted a numerical study to introduce the power augmented shroud which is known as the new design of Omni Directional Guide Vane ODGV on Vertical Axis Wind Turbine VAWT to improve small wind turbine performance. New ODGV design are divided into two segments with same length with the standard guide vane plate and bent at 10° angle. The new design reduces the cut in speed better. The coefficient of power increases about 31.65 compared to the original ODGV design. Furthermore, when it compared to the bare VAWT, it increases about 147.1. Maldonado et al Maldonado, Huerta et al. 2014 studied simulation project to optimize the design configuration of Savonius rotors. A study of speeds and maximum pressures as a function of incidence angles in the windows proposals for the Savonius rotor was proposed. The maximum speed with maxim um pressure were found for the angles α=30° and β=40°. The proposed input configurations in curtains increase the speed of the Savonius rotor and consequently increase the Cp. T he configuration α =30° and β=40 ° can increase the on-coming speed to the Savonius rotor of 5 ms to 8.18 ms increases by 62. Kim et al Kim and Gharib 2013 studied experimentally influence of upstream deflector on performance of straight-bladed VAWTs. The power of wind turbine increases significantly when the turbine placed behind the deflector. Further, there is higher power perpustakaan.uns.ac.id commit to user 5 increase when the turbine placed outside of the near-wake of the deflector. The height of deflector has important influence. The power increases constantly on each turbine positions when the height between deflector and turbine is parallel. Damak et al Damak, Driss et al. 2013 conducted experimental study to increase Savonious wind turbine by proposing a 180° twisted-helical Savonius wind turbine. They studied the aerodynamic behavior of helical Savonius wind turbine. The result shows that the Re variation and overlap ratio affect global characteristics of the helical Savonius wind turbine. Based on the comparison study between the helical and the conventional Savonius wind turbine, the helical Savonius wind turbine meets better performance than the conventional one. Nasef et al Nasef, El-Askary et al. 2013 carried out experimental and numerical studies on the air flow around stationary and rotating Savonius wind turbine. The result represents that SST k- ω turbulence model is the most reliable to simulate the flow pattern around Savonius wind turbine. The changes of Reynold number and diameter affect little on the static torque coefficient of the Savonius wind turbine. Both static torque coefficient and drag coefficient at each angles of turbine increase with the increase of overlap ratio. Overlap causes the pressure coefficient increase on concave blade. As result, turbine met enhancement of turbine performance. The best performance is reached at β = 0.15. It gives power coefficient equals to 0.21 at speed ratio of 0.9. Kumbernuss et al Kumbernuss, Chen et al. 2012 performed experimental study of Savonius wind turbine with various overlap ratios and shift angles. Results determine that higher overlap ratio gives higher impact on increasing the starting characteristic of Savonius wind turbine than any phase shift angles. There is a certain phase shift angle related to a certain velocity that will increase the power coefficient. Furthermore, the recorded data shows an unexpected second performance peak that appeared at higher tip speed ratios. Jeon et al Jeon, Jeong et al. 2014 carried out experimental study of the end plate influence on the aerodynamic performance of helical Savonius wind turbine with a twist angle of 180° of two semicircular buckets. Four helical Savonius wind turbine models were tested by a subsonic open-circuit type wind tunnel. The results show that the maximum power coefficient and tip ratio increased linearly with the increase of end plate ratio up to 1.0. The application both top and bottom circular end plates on turbine increase significantly the power coefficient up to 36 compared without end plates. Table 2.1 summarizes clearly the previous studies which have been explained above. perpustakaan.uns.ac.id commit to user 6 Table 2.1 Resume of Previous Study No. Author Parameters Result Picture 1. Altan et al Altan, Atılgan et al. 2008 Introducing curtain arrangement to improve Savonius rotor. Cp improved up to 38.5 2. Mahmoud et al Mahmoud, El-Haroun et al. 2012 Determining influence of number of blades, stages, overlap ratio, aspect ratio and existence of end plates. two blades, double stage, non-overlap ratio, end plates performed better 3. Wong et al Wong, Chong et al. 2014 Introducing ODGV on VAWT to improve performance. Cp increased about 147.1 4. Maldonado et al Maldonado, Huerta et al. 2014 Simulating project to optimize design configurations of Savonius, which are speeds and angles. The maximum speeds with maximum pressure found for α=30° and β=40° 5. Kim et al Kim and Gharib 2013 Determining the influence of upstream deflector on straight- bladed VAWTs. Power increased significantly with the application of deflector. commit to user 7

2.2. Basic Theory