DIAMETER-TO-CHORD RATIO EFFECT ON THE AERODYNAMIC PERFORMANCE OF SMALL-SCALE DARRIEUS-TYPE STRAIGHT-BLADED VERTICAL AXIS WIND TURBINE

The growing interest in small-scale Darrieus-type straight-bladed vertical axis wind turbines (SB-VAWTs) presents a novel outlook for the conversion of wind energy, departing from horizontal axis wind turbines. The SB-VAWTs are favourable alternative energy sources to generate independent off-grid electrical power in complex wind environments. The current study aims to explore and understand the effect of blade geometry on the efficiency and self-starting ability of the SB-VAWTs. Therefore, three different diameter-to-chord (D/c) ratios have been investigated at various tip speed ratios (lambda). Accordingly, numerical simulation on Darrieus-type SB-VAWTs has been carried out with D/c ratios of 2.5, 3.5 and 4.5 and presented a comparative analysis between their power and torque coefficient. The VAWT with a D/c ratio of 2.5 is conducted in a subsonic wind tunnel of an open circuit type with test section dimensions of 600 mm x 600 mm x 2000 mm to validate and support the numerical findings. The flow physics analysis for all three D/c ratios is also studied by simulations to understand the stability and reliability of SB-VAWTs. An improvement of 13% and 54% is found in the maximum power coefficient by the Darrieus-type SB-VAWT with a D/c ratio of 4.5 as compared to the d/c ratio of 3.5 and 2.5 at lambda=1.8. Smaller D/c ratios exhibit superior self-starting capability in Darrieus-type SB-VAWTs compared to larger D/c ratios at lower lambda values. The outcomes revealed that the proper selection of D/c ratios can enhance the aerodynamic performance and starting torque of Darrieus-type SB-VAWT.