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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]

Vertical axis wind turbines are wind turbines with the rotor axis perpendicular to the ground, designed to harness wind energy for electricity generation. The primary cause of low-efficiency Savonius turbines is the negative torque contribution from the returning blade. A Savonius turbine is a type of turbine characterized by its rotational direction orthogonal to the passing fluid flow and the flow interaction with advancing and returning blades, generating torque primarily through drag forces. Thus, the study proposes a novel design of a cylindrical deflector with splitters and a barrier to offset the flow field to the returning blades. This study aims to maximize the efficiency of conventional Savonius turbines using the cylindrical deflector with splitters and a barrier via a combination of computational fluid dynamics simulations and the Taguchi optimization method. The Taguchi method is used to determine the best combination of specified characteristics such as the length of the barrier (Ls/D), the barrier attachment angle (α), and the geometric shape of the cylinder deflector with a splitter and a barrier. The tip speed ratio (λ) for this study is fixed at λ = 1. The simulations and additive model revealed that the optimal combination in this study is a cylinder deflector with double wake splitters positioned at the top and middle of the deflector. The deflector is oriented parallel to the flow, and a barrier placed at the bottom of the deflector is oriented orthogonal to the flow. The optimal configuration has Ls/D ratio of 0.9 and a barrier attachment angle (α) of 10°. Therefore, the ideal combination was found to produce a power coefficient equivalent to 0.459, indicating that the performance of Savonius turbines increases by around 61% compared to previous studies. [ABSTRACT FROM AUTHOR]

The Savonius wind turbine is a vertical-axis wind turbine invented in 1930s consisting of a cylindrical drum with semi-circular blades attached to the drum. It is popular for its simple design, low costs, and self-starting ability, making it feasible for rural areas. As a rotating device, the blade is considered an important component of the Savonius turbine because it captures energy from an omni-directional wind flow and converts it into mechanical/electrical energy. Blade corrosion can cause a surface degradation which affects the blade's aerodynamic and structural performance. The relation between surface roughness and turbine performance has been addressed in various studies; however, most of these studies focused on horizontal-axis wind turbine. This study analyzed the performance of a static Savonius turbine using a three-dimensional (3D) computer simulation at different blade angle positions through a one-way fluid–structure interaction in terms of static coefficients, von Mises stresses, and deformation with different surface roughness at different wind velocities. The simulation reveals that the position with highest static torque coefficient is when the turbine is resting at 15° with respect to the flow direction. The flow velocity increases the performance; however, the surface roughness deteriorates the flow and decreases the static coefficient. The simulation herein predicts no structural failure, but different materials exhibit different maximum stress and deformation showing the importance of material selection in the turbine blade development. The findings from this study helps to identify a suitable material for the development of the Savonius turbine from a material point of view to minimize turbine downtime and potentially save cost. [ABSTRACT FROM AUTHOR]

The Savonius drag-type wind turbine suffers from poor efficiency due to the adverse negative torques on the returning blades when they rotate against incoming flows. It was proven that using a suitable deflector system has the potential to improve wind turbine efficiency. However, as previously identified in studies, the common drawback of using a flat deflector is the strong wake zone behind it. The present study aims to improve the overall performance of a drag-type wind turbine by using a cylinder deflector with a wake splitter plate to manage and mitigate the detrimental effect of the wake zone behind the deflector. The wake control and suppressing vortex shedding downstream of a circular cylinder have been divided into active and passive flow control techniques. Amid the latter control methods, the adoption of splitter plates has proven to be highly effective for wake control and suppressing vortex shedding behind the cylinder. Unlike previous studies, a cylinder deflector with the wake splitter plate will be utilized instead of the conventional deflectors to improve the efficiency of the wind turbine by disturbing the wake zone downstream of the deflector. To obtain a more efficient configuration, the effect of the variations of the wake splitter length (Ls/D), attachment angle (θwsp), and the count of wake splitters on the outputs such as generated torque coefficient (Cm), power coefficient (CP), and wake zone on the performance of the Savonius rotor were investigated via Computational Fluid Dynamics simulation. The results revealed that cylinder deflectors with the wake splitter increased the Savonius rotor's performance the most for almost all Tip Speed Ratios (TSRs). The average Cm and CP raised considerably up to 15% using a deflector with two wake splitters at TSR = 0.6 compared to the case without deflectors. [ABSTRACT FROM AUTHOR]

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]

The use of Computational Fluid Dynamics as a tool for design and analysis of aerospace systems is well established. Since the results generated by a CFD solver are numerical approximations, the solution is inherently produced with errors and uncertainties. In this paper, a simple fluid flow problem of laminar, incompressible flow past a circular cylinder at Reynolds number of 20 is allowed to be solved by the well-known finite-volume solver ANSYS Fluent. The effect of variations in mesh resolution, domain boundary location and residual criteria settings is investigated. For all the cases, finite, structured meshes of acceptable quality are used. The influence of variables on the cylinder's drag results is analyzed and discussed. An interesting pattern in results has been observed. The study on the variation in mesh resolution showed no presence of mesh independent solution. The study on the variation of the domain distance showed that it is necessary to increase the diameter of the circle several thousand times to obtain a domain independent solution. [ABSTRACT FROM AUTHOR]

This work describes the aerodynamic characteristics of an aircraft wing model with a Rüppell's griffon vulture (RGV)- type winglet. A computational fluid dynamics (CFD) study using ANSYS 15.0 was conducted to study the effect of the RGV winglet on a rectangular wing. The NACA 65(3)-218 wing consists of 660 mm span and 121 mm chord length where the aspect ratio is 5.45. Eight different winglet configurations have been studied. Furthermore, the study is extended to study effect of cant angle and different angles of attack (AOA) to the winglet. A comparative study is done on aerodynamic features such as lift coefficient (CL), drag coefficient (CD), lift/drag ratio (CL/CD) and tip vortices to get the best RGV winglet design. The RGV winglet achieved highest CL compared to other types of winglets configuration. Based on contour plot analysis, the RGV winglet shows lower vortex formation compared to without winglet. The results show about 15 to 30% reduction in drag coefficient and 5 to 25% increase in lift coefficient by using an RGV winglet. [ABSTRACT FROM AUTHOR]

This paper presents a study to achieve discrete entropy consistency using artificial and physical diffusion mechanisms. The study begins with the one-dimensional viscous Burgers equation, specifically looking at the shock results of entropy-conserved fluxes combined with a few choices of artificial and physical viscous diffusions. The approach is then repeated for the Navier–Stokes equations. Overall, it is demonstrated that the artificial viscosity (or entropy) terms are still needed in addition to physical viscosity to achieve entropy consistency in shock predictions, although one of the artificial terms can be dropped for high viscosity or low Reynolds number flow. [ABSTRACT FROM AUTHOR]

In this paper, a study on limited Rotated Richtmyer scheme is performed with a focus on vorticity prediction. It will be mathematically and numerically demonstrated that the Rotated Richtmyer scheme coupled with a TVD limiter can retain both irrotational and rotational flow when solving pure acoustics equations. However, the limited Rotated Richtmyer scheme cannot preserve irrotational flow if the advection terms are included. [ABSTRACT FROM AUTHOR]

In this paper, the discrete phase model (DPM) was introduced to study the fuel injector cavitations process and the macro spray characteristic of three different types of nozzle spray shape with diesel and hybrid biofuel blend for several injection pressures and backpressures. The three types of nozzle spray shapes used were circle, elliptical A type, and elliptical B type. The cavitations' flows inside the injector nozzles were simulated with Computer Fluid Dynamics (CFD) simulations using the cavitations mixture approach. The effect of nozzle spray shape towards the spray characteristic of hybrid biofuel blends is analyzed and compared with the standard diesel. Furthermore, a verification and validation from both the experimental results and numerical results are also presented. The nozzle flow simulation results indicated that the fuel type did not affect the cavitation area vastly, but were more dependent on the nozzle spray shape. In addition, the spray width of the elliptical nozzle shape was higher as compared to the circular spray. Moreover, as the backpressure increased, the spray width downstream increased as well. The spray tip penetration for the elliptical nozzle shape was shorter than the circular nozzle shape due to circular nozzles having smaller nozzle widths and lesser spray cone angles. Thus, this resulted in smaller aerodynamic drag. [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. [ABSTRACT FROM AUTHOR]