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Due to periodic dynamic stall at low tip speed ratios (TSRs), vertical-axis wind turbines (VAWTs) experience notable performance challenges during rotation, which leads to fluctuations in torque and a decrease in energy capture. This research aims to boost the aerodynamic performance of Darrieus VAWTs by employing a leading-edge (LE) prism cylinder (PC) to enhance energy extraction. This novel small-scale device functions as a passive method for controlling flow separation, aiming to energize the boundary layer and adjust the pressure distribution on the blades. Its effectiveness depends on factors such as size, shape, and placement, necessitating careful optimization. A three-dimensional (3D) computational fluid dynamics (CFD) analysis, combined with Taguchi optimization and analysis of variance, is conducted to determine the optimal design parameters for the LE PC tool. This 3D CFD method captures the full complexity of flow dynamics, including vortex structures and wake behavior, leading to more accurate wind turbine performance predictions than two-dimensional (2D) CFD models. The results highlight the crucial role of PC size (Factor A), which contributes nearly 85% to the total contribution factor, while the angle of PC influence is minimal. The optimized rotor demonstrates a 36% increase in maximum average power coefficient (CP) compared to an uncontrolled rotor at TSR = 1.5. However, the effectiveness of this control method diminishes at higher TSRs because the blades encounter angles of attack below the critical stall angle throughout the rotation cycle, naturally preventing flow separation and making the flow separation control method unnecessary. The PC installed on the optimized blade delays flow separation to 55% of the blade chord length, compared to 40% for the base blade. Consequently, the rotor operates efficiently, ensuring consistent, and reliable power generation without flow separation issues. [ABSTRACT FROM AUTHOR]

Savonius turbine is an alternative wind turbine design that has the ability for self-starting from static condition at different blade angle. There are concerns in the structural behavior of the materials used for the Savonius turbine blades under aerodynamic loads. This study aims to optimize the structural and material properties of Savonius wind turbine blades by conducting a comparative analysis of maximum stress and deformation across different materials. This research involves creating detailed numerical models of the turbine blades using Finite Element Analysis to simulate the mechanical behavior under operational loads. Wood, Aluminum, and Steel are investigated to examine its effect of structural performance in the static conditions. In addition to solid isotropic materials, anisotropic materials such as Carbon Fiber and Glass Fiber composites are investigated. Ansys Composite Prepost is used to access the mechanical properties of composites. Initial analysis shows that the deformation is highly dependent on the Young's modulus of each material. Due to the dependency of composite on the fiber properties, a multi-objective optimization is defined to optimize these parameters on a five-layer composite structure to minimize stress, deformation, and weight. It was found that Carbon-Fiber composites exhibit better performance compared to other materials with improvement up to 22% in maximum deformation. These findings highlight the potential for substantial improvements in blade efficiency and durability through careful material selection and optimization. These findings can be utilized for a preliminary design of Savonius wind turbines and other renewable energy sector, where optimizing wind turbine performance is crucial for sustainable energy production to find optimum composite configuration without compromising its aerodynamic performance. [ABSTRACT FROM AUTHOR]

Hydrokinetic turbines experience a harsh hydrodynamic environment with complex vortical flows which increase failure probability. The selection of turbine blade material is extremely critical to maintain its performance, reduce maintenance costs and prevent significant down time. The trade-off between material strength and cost is an important factor that needs to be considered for a hydrokinetic turbine. This article gives a brief overview in existing solution for the materials used for hydrokinetic turbine blades discussing the advantages and disadvantages of various materials in terms of relative performance and life-cycle assessment. This overview can provide a fundamental criterion to researcher and policy makers for selection of materials used in hydrokinetic turbine application. [ABSTRACT FROM AUTHOR]

Shock-capturing finite volume schemes often give rise to anomalous results in hypersonic flow. We present a wide-ranging survey of numerical experiments from 12 different flux functions in one- and two-dimensional contexts. Included is a recently developed function that satisfies the second law of thermodynamics. It is found here that there are at least two kinds of shock instabilities: one is one-dimensional and the other is multidimensional. According to the results, the former does not appear if a flux function satisfies the second law of thermodynamics, and the latter is suppressed by an additional dissipation with a multidimensional character. However, such dissipation has no effect on the one-dimensional mode. Among the flux functions investigated, no universally stable schemes are found that are free from both one- and multidimensional shock instabilities. The appearance of these instabilities depends on the relative positioning of the shock on the grid. DOI: 10.2514/1.33735

The long-term goal in the automotive industry is to reduce fuel consumption and environmental pollution without compromising the aerodynamic performance of the car. Herein, the aerodynamic performance of an in-house designed Shell Eco-Marathon prototype car is analyzed using Computational Fluid Dynamics simulations. Shape optimization of the Shell car is executed to reduce drag by modifying the rear underbody profile and stagnation point position. The effect of one modification to another is studied to determine the changes to overall flow around the car and, more importantly, the lift and drag coefficients. It has been found that the stagnation point height has a higher influence on the aerodynamic performance of the car compared to variations of the rear underbody, with optimum drag reductions of 17% and 10%, respectively. Moreover, combining the two best configurations to the car reduces CD by 25%, and this marks the highest drag reduction achieved in this study. [ABSTRACT FROM AUTHOR]