Numerical Simulation of Cluster of Small Vertical Axis Wind Turbine to Develop a Wind Tree for Low Wind Speed Regime

Abstract

The importance of renewable energy has increased continuously in the recent years due to the growth in the energy demand and a decrease in the fossil fuel resources. Harnessing the low rated wind energy is the promising source so that the wind turbine can be used all year round. Deploying sequence of small turbine is efficient than single bigger size turbine in extracting the low rated wind energy. Hence, in this work, sequence of small vertical axis wind turbine is arranged in the tree like structure and named it as wind tree. The vertical axis type of turbine would be able to perform more efficiently at minimum wind velocity. So, the Helical Savonius vertical axis rotor is deployed in the wind tree which gives the relatively high torque and self-starting even at low wind speeds. The main aim of this work is to analyze numerically the cluster of vertical axis wind turbine in order to improve the average output of the wind tree. In this study, the vertical axis turbines are arranged in the branches of the tree at different plane, so that the wake of one turbine will not affect the turbine in the downstream. The numerical simulation has been studied by using commercially available software ANSYS CFX©. The single helical vertical axis wind turbine is fabricated and tested in the open jet wind tunnel and this experimental result is used for validating the numerical results. In addition to the validation, sensitive study for the grid and the turbulence model has been carried out to improve the simulation quality. Vertical axis wind can accept wind from any direction without any yaw mechanism, so the average performance of this type of turbine in cluster is analyzed by changing the flow (α = 0°, 45° and 90°) of the wind turbine cluster. It is observed from this study that the average power coefficient of the cluster of turbine at the flow angle of 45° has better performance than the other pattern. Moreover, its average power coefficient is 2.3 times higher than the isolated vertical axis wind turbine. These results of the cluster simulation are used to develop an efficient wind tree to harness the low rated wind energy.