چكيده به لاتين
All human actions necessitate energy resources. Currently, a major part of our energy requirements is supplied by fossil fuels, which are faced with uncertainties concerning their availability in the forthcoming decades. However, the combustion of fuels results in adverse environmental aftermaths. Energy of wind falls into one of the clean and renewable energy resources. Wind power is generated using horizontal and vertical axis wind turbines (HAWTs & VAWTs). VAWTs operate appropriately under low wind velocity conditions to generate power in small scales. On the other hand, numerous VAWT designs have been presented to enhance their performance in such circumstances.
In this research, we aim to develop a low-cost model for evaluating the aerodynamic design and performance of Gorlov vertical axis wind turbine. To this end, a double multiple stream tube (DMST) model, which is based on the blade element momentum theory (BEM) has been developed for Darrieus-type straight-bladed and Gorlov VAWTs. The developed models are validated by comparing the obtained results with the available results in the literature; in addition, a comparison has been performed between the Darrieus-type straight-bladed and Gorlov VAWTs from the performance point of view. Furthermore, overall evaluation on the effects of geometrical and operational parameters, including profile of the blade airfoil, number of blades, helical angle, chord length, aspect ratio and free wind velocity have been performed for aerodynamic performance and the torque curves of Gorlov VAWT. Additionally, the initial design parameters of the studied Gorlov VAWT rotor have been optimized based on surrogate-based modeling (SBM) at each tip speed ratio (λ). For this purpose, after determining the effective parameters and their range of changes, the sample matrix has been formed by using design of experiment (DOE) technique from combination of the studied parameters as input variables and the power coefficient (C_P) for each of them which has been calculated by developed DMST model. The surrogate model has been defined by using the obtained results at each tip speed ratio. Afterwards, the best combination of the studied geometric parameters has been extracted from the design space by genetic algorithm method with the aim of maximum turbine power coefficient for each λ of 1.5, 2, 2.5, 3, 3.5, 4 and 4.5.
It has been found that despite the slight reduction of peak power coefficient for Gorlov VAWT compared to Darrieus type, the performance of Gorlov VAWT rotor is better from the effectiveness and fluctuation standpoints according to the torque coefficient curve of helical blade. Considering the results of parametrical evaluation on Gorlov turbine, maximum power coefficient is 0.479 for the tip speed ratio of 3.5 in NACA 0018 airfoil. In addition, it becomes evident that the number of blades and helical angle are important parameters in reducing the aerodynamic loads and improving the rotor stability. As the blade chord length or aspect ratio increases, the performance improves at low λ values; however, it decreases at high λ values and peak C_P. Moreover, self-starting behavior has been improved with increasing the blade chord length or free wind velocity and deteriorated by the usage of thinner airfoils. For the studied Gorlov turbine, the performance curves become wider until free wind velocity reaches to the rated velocity, which is 12 m/s for the studied Gorlov turbine. Comparing the results of optimization procedure, the maximum peak value (C_P=0.503) belonges to optimum Gorlov VAWT design at λ of 3.5. While, the optimum Gorlov VAWT design at λ of 3 has the best C_P curve performance of optimum Gorlov VAWT design curves for less λ values than 3.
