Wind energy is among the most cost-effective renewable energies. Till date, turbines with different configurations had been designed to harness wind power, each having unique superiorities. Darrieus turbines are one of the mostly investigated vertical axis wind turbines using either experimental or numerical methods. Experimental analyses are time consuming works which requires high amount of effort and expenses. Thus, computational fluid dynamics (CFD) methods have been commonly used by scientists and engineers in order of obtaining detailed performance and illustration of the fluid flow. Contrary to the horizontal axis machines, Darrieus turbines are difficult to be analyzed by CFD algorithms due to high pressure and velocity variations which arise from extreme changes in the angle of attack beyond the stall condition at different azimuthal position of the blades. Therefore, more simplified numerical models are generated employing double multiple streamtube (DMS) theory together with additional improvements. QBlade is one of the mostly used numerical methods based on the lifting line free vortex wake method developed for calculating rotor aerodynamics. The main scope of this study is to design a straight bladed Darrieus turbine (D=1028 mm, H=1460 mm, N=3) and to verify the double multiple streamtube theory and QBlade algorithm with the experimental and computational works. Analysis results represented good agreement with the previous studies especially at lower TSR ranges. Compare to the experimental results, an overestimation in the power coefficient is obtained at low free stream speed and high TSR ranges after exceeding the peak point. Sensitivity of the model to the Re number variations have also been outlined.

Increasing energy demand, rising per capita energy use, growing climate problems and other detrimental consequences of energy and environmental issues have prompted scientists and engineers to conduct more studies on the technical feasibility and efficiency of renewable energy conversion systems. Free flow (wind and hydrokinetic) turbines are one of the mostly investigated renewable energy technologies and Darrieus turbines have an exceptional place especially for smaller scale and domestic applications. Many experimental and computational studies have been provided on the performance of Darrieus turbines. However, the number of numerical studies which are more time and cost effective than computational and experimental works are quite limited in the literature. The main objective of this study is to analyze Darrieus turbines at different geometrical and dynamic configurations using numerical QBlade software. In this study, the effect of airfoil selection, number of blades, chord length, solidity and helicity are analyzed in terms of delivering higher performance at straight bladed Darrieus turbines. It has been found that NACA 0020 profile performs better relative to other symmetrical blade sections in vertical axis turbines. Better performance and wider TSR range is obtained for three bladed turbines. Also, increasing chord lengths delivered maximum power at lower tip speed ratio (TSR) ranges. This study is expected contribute site-dependent Darrieus turbine design works at different dimension and dynamic scales for both wind and hydrokinetic applications.

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