Vertical axis wind turbines like Darrieus turbines are very interesting type of wind turbines at domestic zones which have low wind speed, but this type has a low performance compared quantitatively to horizontal axis wind turbines. Further research work is needed to increase its performance to match the higher demand of the power generation in small-scale applications. The main target of the current work is to increase the output power coefficient Cp of a straight-bladed Darrieus wind turbine (H-rotor). The aerodynamic performance assessment will be carried out for 24 new airfoils (symmetric and non symmetric) as the sectional profiles of the Darrieus turbine blade in order to improve the generated power. The present two-dimensional simulation concentrates on eight series of new airfoil shapes. Furthermore, the effect of using a wind-energy collecting structure called "wind-lens" which consists of a diffuser and flanges with Darrieus turbine is computationally examined. The current results indicated to some new shapes suitable for H-rotor Darrieus turbine with considerable performance improvement. It was demonstrated that the symmetric S1046-type is the best performing airfoil for typical tip-speed ratio ranging from 2 to 7. The three-bladed Darrieus turbine with S1046 as a sectional profile introduced a maximum power coefficient C-p,C-max equal to 0.3463. In this study, the performance of three wind lens configurations with different diffuser types is investigated (i.e., flat-panel, curved-surface, and cycloidal-surface). Regarding power augmentation, the results affirmed that adopting diffuser with a cycloidal-surface is more effective than both flat-panel and curved-surface diffusers. The results indicated that the three-bladed Darrieus turbine (consists of S1046 airfoils) equipped with a cycloidalsurface diffuser introduced a maximum power coefficient C-p,C-max and equals to 1.3662 and elucidated power augmentation by a factor of about 3.9 as compared to an open Darrieus turbine (conventional design). (C) 2017 Elsevier Ltd. All rights reserved.