Investigation On Dynamics, Performance And Pitch Angle Optimization Of Vertical-Axis Turbines

To meet increasing global demand for energy, renewable energy sources are endorsed as a solution for the energy crisis. Hydrokinetic energy, the eco-friendly alternative for traditional hydropower that extract kinetic energy from water flow through hydrokinetic turbines has potential to be the replacement for the depleting fossil fuels. Vertical-axis hydrokinetic turbine, with its scalability and omnidirectional characteristic, is a fitting renewable energy supply for off-grid rural areas. However, the existing issue of low performance efficiency hinders the large-scale application of vertical-axis turbine. It is suggested that applying pitch angle to turbine blade is a simple modification that can improve the low performance efficiency of the vertical-axis turbine. This research aims to investigate the effects of pitch angle to vertical-axis turbine dynamics and power performance through numerical simulation. The problems associated with this research are the effects of pitch angle on turbine performance and the optimum pitch design for different operating conditions. Pitch angle effects would be investigated through analyses of simulation results in terms of instantaneous aerodynamic loadings and average power coefficient. Pitch angle optimizations are then performed on the same turbine model to determine optimum pitch angles that maximize turbine performance at different tip speed ratio. To conduct the investigation, a numerical simulation model of a Darrieus type straight-bladed vertical-axis turbine with 3 blades is completed using MATLAB with incorporation of NACA 0021 airfoil data. Blade Element Theory and various assumptions that represent physical turbine operating conditions are applied to create turbine simulation that can adequately predict turbine performance. Validation studies are then conducted by comparing the simulated results with computational fluid dynamics simulation and experimental data, to ensure that the simulation results are accurate and reliable. It is found that, the simulation model is able to simulate results with less than 10% of error at low tip speed ratio. Fixed-pitch angle and dynamic-pitch angle optimizations are then carried out by modifying the numerical model to determine optimum pitch angles. With the simulation results, the effects of pitch angle on the instantaneous angle of attack, tangential force coefficient, normal force coefficient, and power coefficient are analyzed. It is found that fixed-pitch optimization improves on turbine performance efficiency by reducing drag-induced tangential force component in the downstream region. Fixed pitch optimization is able to increase turbine power coefficient by 5.24% at the tip speed ratio of 1. Dynamic-pitch optimization, however, increases turbine power coefficients by maximizing the lift-induced tangential force component while minimizing drag-induced component. Dynamic-pitch optimized turbine model produces power coefficient that improves for 626.92 % compared to zero-pitch turbine model. Due to the limitations and assumptions made, the simulation model is suitable to be applied in fundamental understanding and preliminary design of vertical-axis turbine