Design and 3D CFD studies of non cylindrical helical vertical axis wind turbine on start up and performance analysis for low wind speed

Abstract

The Vertical Axis Wind Turbines (VAWT) are regaining their popularity owing to their omnidirectional and low maintenance characteristics. A new helical vertical axis wind turbine was designed with a non-cylindrical surface of rotation along the rotational axis with the aim of self-starting and reduced torque pulsations. The varying radius geometry with a helical twist along the rotational axis helped to achieve a self-starting turbine operating at a lower TSR range of 2, suitable for stand-alone urban roof-top and pavement installations. A momentum-based model is constructed as a hybrid derivation of the Multiple Streamtube Model and Time Stepping Approach to analyse the preliminary parametric design of the turbine blade geometry. A transient, three-dimensional, dynamic mesh CFD analysis is performed for the proposed new non-cylindrical helical VAWT at a constant free stream wind velocity of 4m/s and 6m/s. The data obtained are processed and compared with the commonly deployed cylindrical helical VAWT at low wind speed conditions. The results show that the new non-cylindrical helical vertical axis wind turbine possesses high starting torque, making it selfstarting at low wind speed. Also, investigations are made on the performance of a new vertical axis wind turbine with non-cylindrical helical turbine blades for an unsteady gusty wind prevailing in urban and suburban environments. Wind gusts are the serious parameters that need to be considered for the aerodynamic study of any wind turbine. In this work, three-dimensional CFD analysis with dynamic mesh has been carried out for two gust velocities of amplitude 2 m/s and 0.6 m/s with a constant free stream velocity of 4 m/s. The results suggest that introducing a gust during the start-up period enhances torque production, allowing it to achieve steady-state faster. Under gusty wind, the turbine reached steady-state 54.71 % faster than under constant wind. The turbine, on iv the other hand, performed well under steady wind during the start-up period on a Cp scale.