Abstract
Darrieus wind turbines are simple lift based machines with exceptionally high efficiencies in terms of power coefficient compared to similar drag based vertical axis turbines. However, in low Reynolds numbers, a notable performance loss was reported. As a potential solution, truncated NACA 0018 airfoil (NACA 0018TC-39) has been introduced with baseline cavity modification to achieve better start-up characteristics and to enhance the low wind speed performance. The baseline cavity will provide an additional benefit of reverse drag at low TSR which is obligatory for low wind speed start-up. Numerical optimization has been carried out on the conceived airfoil NACA 0018TC-39 to find out the effective truncation percentage in terms of the chord. The numerical study has been extended to compare NACA 0018 and NACA 0018TC-39 airfoil for their aerodynamic performances in terms of lift, drag coefficients and separation characteristics. The NACA 0018TC-39 airfoil was incorporated within a non-swept straight bladed Darrieus turbine miniature to experimentally evaluate the performance in terms of dynamic power coefficient, dynamic torque coefficient and static torque coefficient and compared with conventional NACA 0018 airfoil at six different Reynolds numbers 178917, 193827, 208737, 223646, 238556 and 268376. The experimental contrast implied that NACA 0018TC-39 airfoil turbine yielded almost double power coefficients at low Reynolds number compared to conventional NACA 0018 airfoil without hampering its performance at higher Reynolds number.
Highlights
Wind energy is becoming the mainstream form of electrical energy generation with the total installed capacity of 486.8 GW as of 2016 [1] and there has been an increasing trend
The NACA 0018TC-39 airfoil was incorporated within a non-swept straight bladed Darrieus turbine miniature to experimentally evaluate the performance in terms of dynamic power coefficient, dynamic torque coefficient and static torque coefficient and compared with conventional NACA 0018 airfoil at six different Reynolds numbers 178917, 193827, 208737, 223646, 238556 and 268376
The experimental contrast implied that NACA 0018TC-39 airfoil turbine yielded almost double power coefficients at low Reynolds number compared to conventional NACA 0018 airfoil without hampering its performance at higher Reynolds number
Summary
Wind energy is becoming the mainstream form of electrical energy generation with the total installed capacity of 486.8 GW as of 2016 [1] and there has been an increasing trend. With new airfoil design aimed at reducing the manufacturing cost of the blades, these turbines are affordable [10] Apart from these advantages, the development of Darrieus turbines is hindered by their starting performance, pulsating torque, and poor performance in the low wind speed. The study [14] experimentally compared NACA 0018 with varying camber Gottingen airfoils on the performance of Darrieus turbine concluding that peak power coefficient is obtained at lower TSR than symmetric airfoil. Airfoil with trapped vortex concept was put forward for the improvement of starting torque [21] and verified computationally with conventional NACA based rotor [22] early studies on the morphing blades are with flexible sails and sheet metal plates, which have not yielded fruitful results to conduct further research. The power improvement is attributed to the delay in the dynamic stall and reduction in the downstream drag with favorable AoA achieved with the flaps
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