Search Results (101)

The rapid expansion of wind energy into complex and extreme environments has renewed interest in vertical-axis wind turbines (VAWTs) due to their omnidirectional operation, compact footprint, and potential resilience under harsh operating conditions. However, the current understanding of VAWT performance remains fragmented across aerodynamic, structural, operational, and application-specific studies. This systematic review aims to synthesize and critically evaluate VAWT research with environmental stressors as the central organizing framework, addressing performance behavior, adaptation challenges, and future research pathways. Literature searches were conducted in the Web of Science Core Collection, Scopus, IEEE Xplore, ScienceDirect, and SpringerLink databases, with Google Scholar used as a supplementary source, covering publications from 2000 to January 2026. Eligible studies focused on VAWTs operating under non-standard or extreme conditions, including icing, offshore, desert, high-turbulence, and thermally severe environments. A systematic quality assessment was applied to evaluate methodological rigor and environmental characterization, and the findings were synthesized using a qualitative–quantitative hybrid approach; no formal meta-analysis was performed. The review reveals substantial advances in unsteady aerodynamics, numerical modeling, and control strategies, but also identifies persistent discrepancies between high-fidelity simulations and real-world performance due to simplified modeling assumptions and limited full-scale experimental validation. Quantitative findings indicate that high turbulence can decrease the power output of large VAWTs by 23–42%, dust and sand in arid environments can reduce torque and power by ~25%, and air temperature increases from 15 °C to 60 °C can reduce the power coefficient of VAWTs by about 38%. Emerging approaches, including artificial intelligence-assisted design, adaptive turbine architectures, and climate-aware methodologies, show promise in addressing these limitations. The findings highlight the urgent need for coordinated long-term field measurements, improved multi-physics modeling, and interdisciplinary research to enhance the reliability and scalability of VAWTs in extreme environments. This review was not registered. Full article

This study presents a two-dimensional computational fluid dynamics analysis of a vertical-axis Savonius-type wind turbine under atmospheric conditions representative of an educational environment located in the Ecuadorian Andean region. Unlike previous studies conducted under sea-level meteorological conditions, this research is performed under high-altitude conditions (2723 m a.s.l.). The unsteady flow around the rotor was simulated using a two-dimensional approach based on the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations, discretized with the finite volume method and coupled with the k–ω Shear Stress Transport (SST) turbulence model. The rotor rotation was modeled using sliding mesh technique, employing a second-order implicit time scheme to ensure numerical stability and adequate temporal resolution. The numerical model was configured for a tip speed ratio of 0.8 and a wind speed of 3.9 m/s. The time step was defined based on a constant angular advancement of the rotor per time iteration, ensuring numerical stability and adequate temporal resolution. The aerodynamic torque was obtained by integrating the pressure and viscous forces acting on the blades, allowing the calculation of the mechanical power generated and the power coefficient. The results showed a periodic and stable torque behavior after the initial transient cycles, yielding an average torque of 0.7687 N·m and a mechanical power of 5.17 W, while the power coefficient reached a value of 0.2102. Analysis of the flow fields revealed the formation of a low-velocity wake downstream of the rotor, regions of high turbulent kinetic energy associated with periodic vortex shedding, and a significant pressure difference between the advancing and returning blades, confirming that turbine operation is dominated by drag forces. The numerical results were validated through comparison with previous studies, showing good agreement and demonstrating the reliability of the proposed Computational Fluid Dynamics (CFD) approach. This study highlights the potential of Savonius turbines for low-power applications in urban and educational environments, as well as the usefulness of CFD as a tool for evaluating and optimizing their aerodynamic performance. Full article

Background/Objectives: Bacterial meningitis is a severe disease with a fatality rate of 5–50%. It is mainly caused by Streptococcus pneumoniae or Neisseria meningitidis, which can also cause simultaneous infections outside the central nervous system. Toll-like receptors (TLRs) have an important role in the innate immune system. The TLR2 subfamily comprises the four highly homologous members TLR1, TLR2, TLR6, and TLR10, which also have an important immunomodulatory role in infectious diseases. Methods: The study cohort consists of 190 bacterial meningitis patients aged 1 to 147 months from randomized clinical trials and 268 controls from Luanda, Angola. Polymorphisms of TLR2 (rs111200466) and TLR10 (rs10856837 and rs11096956) were determined using PCR-based methods and Sanger sequencing. The genotyping results were analyzed together with clinical data to determine whether gene polymorphisms of TLR2 and TLR10 are associated with susceptibility and outcome of bacterial meningitis in Angolan children. Results: At admission and during hospitalization, patients with pneumococcal meningitis carrying a variant (ins/del or del/del) of TLR2 rs111200466 had a significantly lower risk of coexisting infections (OR 0.27; 95% CI 0.11–0.65; p = 0.004), particularly pneumonia (OR 0.18; 95% CI 0.06–0.49; p = 0.001). In addition, haplotype analysis demonstrated that a variant genotype of TLR2 rs111200466 together with a wildtype of TLR10 SNPs (rs10856837 and rs11096956) may protect against coexisting pneumonia (OR 0.2; 95% CI 0.06–0.6; p = 0.007). Conclusions: This study suggests an association between coexisting infection and genetic variation in TLR2 and TLR10 of bacterial meningitis in Angolan children. Full article

This study presents a numerical and experimental analysis of vertical-axis Cycloidal rotors ($R_C$) versus Savonius rotors ($R_S$), with and without coupling to a Gorlov rotor ($R_G$), designed to operate under low wind speed conditions of 2.5 m/s. Using transient Computational Fluid Dynamics (CFD), numerical mesh stability was evaluated as a function of rotor power, achieving convergence with 8,199,923 nodes and a stable angular momentum after 10 s. In the experimental phase, electrical characterization was conducted by coupling the rotors to a direct current generator, allowing for the determination of the optimal electrical load as a function of rotational speed (RPM). The results show that electrical power output and power coefficient (Cp) increased with rotational speed, reaching a maximum of 39.22 mW and Cp = 0.126 for the Cycloidal rotor ($R_C{\theta }_{R}45$), which exhibited the best overall performance. When coupling a Gorlov rotor with a torsion angle of 90° ($R_G{\theta }_{G}90$), maximum power of 52.45 mW and Cp = 0.168 were obtained for the hybrid configuration $R_C,{\theta }_{R}0$-$R_G{\theta }_{G}90$, confirming the aerodynamic and electrical performance improvement due to geometric coupling compared to a standalone Savonius rotor. The comparison between the numerical and experimental results showed consistent trends in Cp values, with slight deviations attributed to friction and alignment effects during physical testing. This study proposes an integrated methodology in renewable energy technologies that combines 3D transient CFD simulation with experimental characterization under variable electrical load conditions to determine the optimal operating power of novel Cycloidal rotors for low-wind-speed applications. Full article

This study presents a compact, 3D-printed Savonius wind turbine rotor incorporating pointed deflectors to enhance concave-side airflow and mitigate blade-edge vortex formation. The prototype, fabricated from ABS plastic, was experimentally evaluated in an Eiffel-type wind tunnel under low-speed wind conditions (3, 4, and 5 m/s), with blockage effects taken into account. Flow visualization revealed improved airflow attachment and pressure concentration on the concave blade surfaces, increasing drag asymmetry and torque generation. Corresponding power coefficients with applied blockage ratio were observed to be 0.181, 0.185 and 0.186, while torque coefficients with applied blockage ratio were observed to be 0.385, 0.374 and 0.375 at each wind speed and optimal tip-speed ratio, respectively, and were compared with previously reported computational results. The optimal operating tip-speed ratios identified for the torque and power coefficients were remarkably close, enabling efficient torque and power generation during operation. The experimental findings validate earlier numerical predictions and underscore the importance of physical testing in assessing turbine performance. Observed deviations between predicted and experimental coefficients suggest that fabrication parameters may influence prototype performance and warrant further investigation. Overall, the results demonstrate the technical viability of 3D-printed Savonius turbines for small-scale urban energy harvesting applications in the Philippines. Full article

This study rigorously evaluated the integration of energy-harvesting systems within electric vehicles to prolong battery service life. A laboratory-scale system was configured utilizing a scale electric vehicle with a 12.6 V lithium-polymer (Li-Po) battery alongside an automated control platform to precisely estimate the real-time State of Charge (SoC) through monitoring of current, voltage, and temperature of the vehicle battery under three distinct driving conditions: (A) constant velocity at 30 km/h, (B) variable velocities exhibiting a sawtooth profile, and (C) random speed variations. Wind energy was harvested employing Savonius rotor microturbines, with assessments conducted on efficiency losses and drag coefficients to determine the net power yield for each operational profile, which was found to be marginally positive. Considering the energy consumption of electric vehicles based on 2017 U.S. EPA fuel economy data, the maximal recovered energy corresponded to 0.0833% of auxiliary system demand, while the minimal recovery was 0.0398%. These results substantiated the necessity for continued research into sustainable energy management frameworks for electric vehicles. They emphasized the critical importance of optimizing the incorporation of renewable energy technologies to mitigate the environmental ramifications of the transportation sector. Full article

This study presents the geometric optimization of a Savonius-type VAWT with multi-element blade profiles using a full factorial design integrated with RSM. Two crucial geometric parameters, the blade twist angle ($\gamma$) and the aspect ratio ($AR$), were systematically varied to assess their influence on the power coefficient ($C_p$). Experimental measurements were performed in a controlled wind tunnel environment, and a second-order regression equation was used to model the resulting data. The optimization approach identified the combination of $\gamma$ and $AR$ that maximized $C_p$. The optimal configuration was achieved with a $\gamma$ of 30° and an $AR$ of 2.0, for which the experimentally measured power coefficient ($C_p$) reached a value of 0.2326. The results confirm that lower twist angles and higher aspect ratios enhance aerodynamic efficiency, reduce manufacturing complexity, and improve structural reliability. These findings highlight the potential of Savonius turbines as competitive solutions for small-scale energy harvesting in low-wind-speed environments. Moreover, the identified optimal configuration provides a basis for future work that focuses on scaling the design, integrating power transmission and electrical generation components, and validating performance under real operating conditions. Full article

This paper reviews and analyzes three types of vertical-axis wind rotors: the classic Savonius, spiral Savonius, and Darrieus designs. Using numerical modeling methods, including computational fluid dynamics (CFD), their aerodynamic characteristics, power output, and efficiency under different operating conditions are examined. Key parameters such as lift, drag, torque, and power coefficient are compared to identify the strengths and weaknesses of each rotor. Results highlight that the Darrieus rotor demonstrates the highest efficiency at higher wind speeds due to lift-based operation, while the spiral Savonius offers improved stability, smoother torque characteristics, and adaptability in turbulent or low-wind environments. The classic Savonius, though less efficient, remains simple, cost-effective, and suitable for small-scale urban applications where reliability is prioritized over high performance. In addition, the study outlines the importance of blade geometry, tip speed ratio, and advanced materials in enhancing rotor durability and efficiency. The integration of modern optimization approaches, such as CFD-based design improvements and machine learning techniques, is emphasized as a promising pathway for developing more reliable and sustainable vertical-axis wind turbines. Although the primary analysis relies on numerical simulations, the observed performance trends are consistent with findings reported in experimental studies, indicating that the results are practically meaningful for design screening, technology selection, and siting decisions. Unlike prior studies that analyze Savonius and Darrieus rotors in isolation or under heterogeneous setups, this work (i) establishes a harmonized, fully specified CFD configuration (common domain, BCs, turbulence/near-wall treatment, time-stepping) enabling like-for-like comparison; (ii) couples the transient aerodynamic loads p(θ,t) into a dynamic FEA + fatigue pipeline (rainflow + Miner with mean-stress correction), going beyond static loading proxies; (iii) quantifies a prototype-stage materials choice rationale (aluminum) with a validated migration path to orthotropic composites; and (iv) reports reproducible wake/torque metrics that are cross-checked against mature models (DMST/actuator-cylinder), providing design-ready envelopes for small/medium VAWTs. Overall, the work provides recommendations for selecting rotor types under different wind conditions and operational scenarios to maximize energy conversion performance and long-term reliability. Full article

The present work investigated numerically turbulent airflows over a hybrid Darrieus/Savonius vertical axis wind turbine. Firstly, the isolated turbines were validated in comparison to previous studies from the literature. Later, new recommendations were obtained for the simulation of a hybrid turbine subject to turbulent airflow. The numerical simulations consisted of the solution of time-averaged equations of mass and momentum in x and y directions using the finite volume method, available in the commercial code Ansys Fluent (version 2022 R1). For closure of turbulence, the k − ω SST (Shear Stress Transport) model was employed. For lower magnitudes of tip speed ratio (TSR), the hybrid turbine improved the power coefficient (C_P) compared to the Darrieus turbine (e.g., by 70% at TSR = 0.75), thereby demonstrating the self-starting capability of the hybrid configuration. Unexpectedly, at the optimal TSR = 1.5, the hybrid turbine performed about 6.5% better than the Darrieus turbine, indicating that the balance between the additional power generated by the Savonius rotor and losses caused by flow disturbances in the hybrid configuration was positive. As a novelty, results highlighted the role of each rotor (Darrieus and Savonius) for the performance of the hybrid turbine by comparing it with isolated Darrieus and Savonius turbines under the same conditions. Full article

Hybrid marine energy platforms that integrate wave energy converters (WECs) and hydrokinetic turbines (HKTs) offer potential to improve energy yield and system stability in marine environments. This study identifies a compatible WEC–HKT integrated system concept through a structured concept selection framework based on multi-criteria decision analysis (MCDA). The framework follows a two-stage process: individual technology assessment using eight criteria (efficiency, TRL, self-starting capability, structural simplicity, integration feasibility, environmental adaptability, installation complexity, and indicative cost) and pairing evaluation using five integration-focused criteria (structural compatibility, PTO feasibility, mooring synergy, co-location feasibility, and control compatibility). Criterion weights were assigned through a four-level importance framework based on expert judgment from 11 specialists, with unequal weights for the individual evaluation and equal weights for the integration stage. Four WEC types (oscillating water column, point absorber, overtopping wave energy converter, and oscillating wave surge converter) and four HKT types (Darrieus, Gorlov, Savonius, and hybrid Savonius–Darrieus rotor) are assessed using literature-derived scoring and weighted ranking. The results show that the oscillating water column achieved the highest weighted score among the WECs with 4.05, slightly ahead of the point absorber, which scored 3.85. For the HKTs, the Savonius rotor led with a score of 4.05, surpassing the hybrid Savonius–Darrieus rotor, which obtained 3.50, by 0.55 points. In the pairing stage, the OWC–Savonius configuration achieved the highest integration score of 4.2, surpassing the PA–Savonius combination, which scored 3.4, by 0.8 points. This combination demonstrates favorable structural layout, PTO independence, and mooring simplicity, making it the most promising option for early-stage hybrid platform development. Full article

Savonius drag-based rotors, a type of vertical-axis wind turbine (VAWT), are well-suited for urban environments—particularly residential rooftops—owing to their compact design and ability to capture wind from all directions. However, their relatively low efficiency and narrow operational range pose significant challenges, such as limited energy output under variable wind conditions and reduced performance across a broad range of tip speed ratios. To address these issues, this study explores flow augmentation using strategically placed deflectors, referred to as Wind Accelerators and Guiding Rotor Houses (WAG-RHs). Four different configurations, including double, triple, oblique, and straight designs, were evaluated against both omni-directional guide vanes (ODGVs) and a conventional rotor. The findings show that the ODGV configuration successfully extends the operational range from a tip speed ratio of 0.5 to 0.6—termed the extended performance point (EPP)—and increases the power coefficient ($C_p$) by up to 300% compared to the conventional design. Among all setups, the straight WAG-RH configuration proved most effective, not only achieving the EPP but also delivering a 385% and 264.3% increase in local and AVE $C_p$ values, respectively compared to the conventional rotor. It also outperformed the ODGV-equipped rotor by 25%, thanks to its radial and dual-plane arrangement. Full article

Utilizing pipeline Savonius hydro turbines driven by the pressure difference in water flow in the irrigation pipelines to generate electricity can achieve stable and reliable charging of the sensor battery, thereby addressing autonomous energy supply concerns. However, due to the low energy capture efficiency of the Savonius turbine with a small pressure difference, it is necessary to optimally design the internal flow channel structure to improve its efficiency and achieve a more miniaturized overall equipment, which has extremely high engineering application value. This study investigates the Savonius turbine, installed within the irrigation pipeline operating under specific conditions (diameter: 60 mm; flow rate: 15 m³/h; inlet pressure: 0.2 MPa; outlet pressure ≤ 0.05 MPa). A validated Computational Fluid Dynamics numerical model was developed to generate 200 datasets for a subsequent structural optimization process utilizing a Bayesian-optimized broad learning technique. The optimal structural parameters for maximum efficiency are a deflector angle of 10°, an aspect ratio of 0.775, and three blades, resulting in a maximum efficiency of 21.73% at a rotational speed of 1098 r/min. For the maximum power coefficient, the optimal combination is a deflector angle of 10°, a height-to-diameter ratio of 0.9, and three blades, yielding a peak power coefficient of 0.1859 at a rotational speed of 600 r/min. Full article

This study investigated the performance of Savonius hydrokinetic turbine blades through three-dimensional computational fluid dynamics simulations conducted at a fixed tip speed ratio of 0.87. A multi-factor experimental design was employed to construct 45 V-shaped rotor blade models, systematically examining the effects of a V-angle (30–140°) and straight-edge length (0.24 L–0.62 L) on hydrodynamic performance, where L = 25.46 mm (the baseline length of the straight edge). The results indicate that, as the V-angle and the straight-edge length vary independently, the performance of each blade first increases and then decreases. At TSR = 0.87, the maximum power coefficient (C_P) of 0.2345 is achieved by the blade with a 70° V-Angle and a straight edge length of 0.335 L. Pressure and velocity field analyses reveal that appropriate geometric adjustments can optimize the high-pressure zone on the advancing blade and suppress negative torque on the returning blade, thereby increasing net output. The influence mechanisms of the V-angle and straight-edge length variations on blade performance were further explored and summarized through a comparative analysis of the vorticity characteristics. This study established a detailed performance dataset, providing theoretical and empirical support for V-shaped rotor blade design studies and offering engineering guidance for the effective use of low-flow hydropower. Full article

This study presents the development of an adaptive control system for aerodynamic flaps of a two-tier vertical-axis Savonius wind rotor to improve performance under variable wind loads. The approach includes detailed kinematic and dynamic modeling of the flap actuation mechanism, accounting for real-world nonlinearities such as backlash, friction, and impact loads. The mechanical transmission system is analyzed to evaluate the influence of design parameters on system dynamics and control accuracy. A mathematical model of an adaptive PID controller is proposed, capable of real-time adjustment of gain parameters based on external wind torque. Numerical simulations under various wind conditions demonstrate that adaptive tuning significantly enhances system stability, reduces overshoot, and ensures faster response compared to fixed-parameter controllers. Sensitivity analysis confirms the importance of mass distribution, mechanical stiffness, and damping in minimizing vibrations and ensuring durability. The developed system provides a reliable solution for efficient wind energy conversion in dynamic environments, including urban and coastal applications. Full article

Ocean energy represents a promising resource for renewable energy generation. Hydrokinetic turbines (HKTs) provide a sustainable method to extract energy from ocean currents. However, turbine efficiency remains limited, particularly in marine environments with low flow velocities. A parametric evaluation of blade configurations is conducted in this study to assess their effect on the power and torque performance of a double-stage drag-based Savonius HKT. Numerical simulations are conducted using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the k-ω SST turbulence model. The numerical model is validated against published data, and analyses on mesh density, domain size, and time step are performed to ensure accuracy. Three blade configurations—(0°, 0°), (0°, 45°), and (0°, 90°) are evaluated under flow velocities of 0.6 m/s, 0.8 m/s, and 1.0 m/s. Results indicate that blade configuration significantly affects turbine performance. The (0°, 0°) configuration performs best at high flow velocity (1.0 m/s), while the (0°, 45°) setup achieves the highest efficiency at 0.6 m/s. The (0°, 90°) configuration performs the least effectively across all conditions. A similar performance trend is observed for the torque coefficient. This study recommends selecting blade configurations based on flow velocity, providing design guidance for double-stage HKTs operating in varying marine conditions. Full article