Abstract
Vertical axis wind turbines (VAWTs) are used to convert wind energy to mechanical output or electricity. Vertical axis wind turbines are favorable at buildings as it can receive wind from any direction, have a design that can be integrated simply with building architecture and they have better response in turbulent wind flow which is common in urban areas. Using a calculation code based on the Double Multiple Stream Tube theory, symmetrical straight-bladed NACA0012 wind turbine performance was evaluated. The induction factor for both upwind and downwind zone is determined with the aid of a root-finding algorithm. This numerical analysis highlighted how turbine performance is strongly influenced by the wind speed (Reynolds number) and rotor solidity (turbine radius and blade chord length). Also a dimensional analysis is introduced and is to be considered in such a way to generalize the design for different turbine specifications. One of the qualities provided by dimensional analysis is that geometrically similar turbines will produce the same non-dimensional results. This allows one to make comparison between different sizes wind turbines in terms of power output and other related variables. One of the main problems affecting the turbine performance and dynamics is the torque ripple phenomena. So in this paper a turbine design configuration is introduced in order to decrease the turbine torque fluctuation. This design is carried out by constructing more similar turbine units (stages) on the vertical axis on top of each other with different orientation phase angles. The results showed that using even number of turbine assembly is better than odd number to avoid torque fluctuation and mechanical vibrations acting on the turbine. Also it is preferred to use four turbine stages as the eight stages will have no sensible effect on decreasing the torque fluctuation.
Highlights
Paraschivoiu et al [1] presented an optimal computation of blade’s pitch angle of an H-D Darrieus wind turbine to obtain maximum torque with some results presented using a 7 kW prototype
Estimation of the performance of Darrieus type Vertical axis wind turbines (VAWTs) is very tough, as the blades rotate in the three-dimensional space around the rotor which results in several flow phenomena such as dynamic stall, flow separation, wake flow and natural incapability to self-starting
To introduce a design of multi stage vertical axis wind turbine to decrease turbine torque ripple phenomena and avoid the mechanical vibrations acting on the turbine
Summary
Paraschivoiu et al [1] presented an optimal computation of blade’s pitch angle of an H-D Darrieus wind turbine to obtain maximum torque with some results presented using a 7 kW prototype. Dominy et al [2] in their presentation of vertical axis wind turbines explained the potential advantages of using Darrieus type wind turbines in the small scale and domestic applications where the cost and reliability are very important points in addition to the simplicity of design structure, generator and control system. Sabaeifard et al [8] discussed the potential of using VAWT for buildings They explained the aerodynamics and the performance of small scale Darrieus type straight-bladed VAWT through a computational and an experimental study. Frank et al [15] studied the aerodynamic performance and wake dynamics of a Darrieus-type vertical-axis wind turbine consisting of two straight blades which was simulated using Brown’s vortices transport model. Their analysis was performed on three different wind field data sets: measured fields, data generated by a standard wind field model and data generated by an alternative model based on continuous time random walks, which grasps the intermittent structure of atmospheric turbulence in a better way
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