Wind is an important renewable energy resource, which can be extracted for power generation by horizontal and vertical axis wind turbines (VAWTs). VAWTs can be installed in low wind speed regimes for small-scale power generation. However, for better performance in such a scenario, an improved rotor blade configuration is essential. This paper investigates the performances of an asymmetric blade H-Darrieus rotor with a blade span constant relative thickness (RT) and a variable thickness (VT) at different low wind speeds between 4 and 6 m/s. Both static and steady-state performances have been evaluated. Different blade span thickness to chord ratios (t/c) of 30% and 45% (constant RT case) are considered by increasing the blade thickness of the considered base profile NACA 63-415 while keeping the chord length same (5.0 cm). After determining the optimal blade RT, a new blade span variable thickness (VT) H-Darrieus rotor has been designed with a thicker portion (t/c =37.5%) on the top end and a thinner portion (t/c = 22.5%) on the bottom end of the blade, i.e., the thickness of the blade profile throughout the blade span is not the same. The thickness gradually decreases from top to bottom of the blades. The effects of all the thickness modifications have been studied with respect to the performance improvement of the H-Darrieus rotor. It has been shown that constant blade span RT (t/c = 45%) can largely improve the starting characteristics of the asymmetric blade H-Darrieus rotor, whereas blade span VT design can result in better power coefficients of the same in low wind speed conditions. Furthermore, an attempt has also been made to study the fluctuations of steady state torque at the selected wind speeds for understanding the stability and smoothness of operation. Moreover, the fluctuations of power and torque coefficients due to steady turbulence intensity and flow non-uniformity over a constant wind speed have also been demonstrated to connect with real-life applications of the H-Darrieus rotor.

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An asymmetric blade vertical-axis wind turbine (VAWT) is one of the emerging technologies for harvesting power in the built environment, which has low wind speed. Although asymmetric blade improves VAWT's performance, the effect of blade pitch angle on its design is hardly ascertained. In this paper, unsteady 2D Reynolds-averaged Navier-Stokes CFD simulations are carried out to investigate the effect of blade pitch angle on the aerodynamic performance of a NACA 63-415 asymmetric blade H-Darrieus VAWT at a low wind speed of 6.0 m/s. Its detailed flow physics at different operating and pitch angle conditions is investigated, and important performance insights are obtained to elucidate its desired blade pitch for performance improvement. The present study shows that positive pitch angle (+ 5°) improves the turbine performance in upwind position, whereas negative pitch angle (− 5°) augments the turbine performance in downwind position as well as causes less wake effect than positive pitch angle. Further, optimal pitch angle (+ 5°) is found out at which the maximum power coefficient of 0.271 is obtained for an operating tip speed ratio 2.4. The present study delineates how desired blade pitch improves the performance of asymmetric blade VAWT for sustainable power generation in the built environment.

For urban areas, small-scale vertical axis wind turbine (VAWT) is a promising energy harvester due to its compact structure. However, VAWT's performance is inferior in low wind speed of urban environment. Selection of proper design and operational parameters can give a desirable power output under such condition. In this paper, effect of trailing edge blade twist on aerodynamic performance of an asymmetric blade H-Darrieus VAWT at a wind speed (6.0 m/s) is investigated using 2D numerical simulation. Important aerodynamic parameters considering blade twists have been analysed. Although blade twist has not increased power coefficient magnificently, the same is improved with blade twist of 1º. However, further increase of the latter reduces the turbine performance. A maximum power coefficient of 0.171 is obtained at tip speed ratio 2.4 for 1º blade twist configuration. Hence, the present study shows that blade twist should be very low for low wind speed application of H-Darrieus VAWT.