A two-dimensional numerical investigation was conducted to evaluate the effects of plasma actuators (PLA) on the aerodynamic performance of a Darrieus vertical-axis wind turbine (VAWT). In the present study, PLAs mounted on turbine blades are employed to control flow separation. First, the flow field around the turbine and the induced field produced by the PLA are numerically simulated and validated. The influences of applied voltage, electrode length, and position on the power curve and flow features are explored. The performance of the PLA under optimal conditions is then evaluated for rotors with two to five blades, and the corresponding power curves are obtained. The results indicate that for a three-bladed rotor, the optimal use of the PLA increases the average power coefficient from 0.241 to 0.447. Moreover, due to the significant effectiveness of the PLA at low tip-speed ratios, the operational stability of the turbine is improved, and the difference between the maximum and minimum power coefficients of the three-bladed rotor over the tip-speed ratio (TSR) range of 1.64 to 3.3 is reduced from 0.24 to 0.09.

Gravitational water vortex turbines (GWVTs) have emerged as promising hydrokinetic technology for energy extraction in riverine systems characterized by low flow velocity and ultra-low head, where conventional hydropower solutions are not feasible. In this study, a three-dimensional computational fluid dynamics (CFD) model is developed to investigate turbine performance within a conical basin configuration. The numerical framework, validated against published reference data, is used to systematically evaluate the influence of airfoil axial spacing, chord sizing, and airfoil profile, on vortex structure and power coefficient. The results demonstrate that basin-induced flow control plays a critical role in enhancing tangential momentum transfer to the rotor. Among the investigated cases, a configuration employing a NACA0024 ducted airfoil with a chord size of 35 mm and an axial spacing of 50 mm yielded the highest power coefficient of 0.419 compared to the baseline basin power coefficient of 0.313 and reached a maximum value of 0.736 at higher inlet velocities. Performance analysis based on tip speed ratio (TSR) further identified an optimal low-TSR operating range consistent with gravitational water vortex turbine characteristics. Compared with previous GWVT studies that focus on turbine geometry, the present work highlights the effectiveness of basin wall airfoil design as an impactful strategy for performance enhancement in low-head hydrokinetic applications.

• Hybrid HAWT–PV prototype with interchangeable 3-, 4-, and 5-blade rotors is experimentally and numerically characterized for compact small-scale generation. • Blade-number effect clarified: more blades reduce vibration and shift peak response to higher frequencies, while 5 blades give the highest torque and C p with the most stable electrical output. • Validated CFD–experiment agreement shows smoother, more uniform flow at higher solidity, and the 5-blade hybrid delivers up to 28.9 W, outperforming stand-alone wind or solar units in daily energy yield. Global growth in electricity demand and the environmental impact of fossil-fuel–based generation motivate the development of compact, efficient, and structurally robust small-scale renewable systems. This study develops and validates an integrated hybrid generation system that structurally combines a horizontal-axis wind turbine (HAWT) with 3-, 4-, and 5-blade rotors and a photovoltaic panel within a single support framework. The objective is to design a compact prototype, experimentally characterize its aerodynamic and electrical performance, and evaluate its structural integrity through numerical simulation. The development method integrates experimental testing, computational fluid dynamics (CFD), structural modal and harmonic response analysis using numerical simulation, and GIS-based feasibility assessment incorporating land–energy planning and seasonal wind variability. Experimental results show that the 3-blade rotor achieves higher rotational speed and a broader, nearly linear TSR range, making it suitable for stronger wind conditions. The 5-blade rotor produces the highest torque and power coefficient ( C P ) while maintaining the lowest vibration amplitude and more stable electrical output. Harmonic analysis indicates that increasing blade count reduces vibration amplitude and shifts peak response toward higher frequencies, improving operational stability. CFD simulations corroborate these findings, revealing smoother and more uniform flow fields with increasing rotor solidity. When integrated with the solar panel, the 5-blade configuration delivers a maximum combined electrical output of 28.9 W. The results demonstrate that structural integration, supported by coupled experimental–numerical validation and geo-spatial feasibility analysis, enhances daily energy yield and provides a practical design pathway for small-scale coastal hybrid renewable energy systems.

This paper investigates the sum spectral efficiency (SE) and total energy efficiency (EE) of the active reconfigurable intelligent surface (aRIS)-assisted cell-free (CF) massive multiple-input multiple-output (mMIMO) over temporal and spatially correlated channels. Multiple aRISs are deployed between numerous access points (APs) and mobile users to enhance the signals. The active reflective elements (REs) amplify and vary the signal phase. The continuously evolving channel creates a situation, where the channel differs during training and data transmission. We characterize the joint impact of multi-user interference (MUI), pilot contamination (PC), channel aging (CA), and active RIS noise amplification (RNA). The desired signal is enhanced as the reflected signal amplitude and REs per aRIS increase. However, the PC, MUI, CA, and RNA also grow– constraining the SE. Also, the network power consumption increases. An alternating optimization framework based on the weighted minimum mean square error and fractional programming is proposed to optimize the transmit power and reflection coefficients (RCs) with the objective of maximizing the sum SE. It is demonstrated that the number of APs and REs can be reduced by deploying aRISs. The proposed power and RC optimization algorithms considerably improves the sum SE. The trade-off analysis between the total EE and sum SE shows that the envelope of the operating region of the CF mMIMO is expanded by deploying multiple aRISs.

Algebraic estimation-based model-free control for variable-speed wind turbines

Blade shape optimization of floating offshore vertical axis wind turbines for maximum power coefficient under platform pitch motion

Savonius wind turbine (SWT) optimization via machine learning and optimization techniques has attracted increasing attention; however, most existing studies rely on limited datasets that cover only specific geometric parameters or operating conditions. This limitation constrains the comprehensive exploration of the Savonius wind turbine design space. Therefore, the present study constructs a comprehensive multisource dataset covering the key geometric parameters and operating conditions of SWT. Accordingly, an iterative optimization framework integrating artificial neural networks (ANN), genetic algorithms (GA), and computational fluid dynamics (CFD) is developed. The performed CFD simulations are employed to enrich the dataset by filling critical data gaps. Consequently, two high-accuracy ANN surrogate models are established for straight and twisted SWTs, achieving correlation coefficients of up to 0.98. Accordingly, optimizing the developed models results in optimal designs with maximum power coefficients of 0.1856 and 0.1927 for straight and twisted SWTs, respectively. Employing the developed ANN models with Monte Carlo-based sensitivity analysis enables the quantification of influence percentage of each design parameter and operating condition on SWT performance. Furthermore, the optimal designs are fabricated and experimentally tested under different operating conditions. The experimental measurements show good agreement with the ANN model predictions, ensuring the accuracy of the developed ANN-GA-CFD framework.

Tidal kinetic energy is characterized by its bidirectional flow nature, which raises unique challenges for efficient power conversion. Conventional tidal current energy systems commonly employ horizontal-axis open-propeller turbines, often requiring additional mechanisms to accommodate changes in flow direction. This study presents the development of a theoretical analysis model aimed at improving the performance of a bidirectional ducted tidal turbine. A systematic design methodology for a bidirectional turbine rotor is proposed, emphasizing simplicity, mechanical reliability, and obedience to fundamental turbomachinery principles. The theoretical framework incorporates actuator disk theory to establish a performance reference, resulting in a maximum power coefficient of 0.385 based on the maximum duct area. This value is proposed as the ducted Betz limit for ducted tidal turbines. A model-scale experimental validation of the bidirectional duct–turbine system was conducted at a blockage ratio of 0.105. The experimental results yielded a maximum power coefficient of 0.093, which, although significantly lower than the theoretical limit, confirms the applicability of the proposed ducted Betz limit as a meaningful performance benchmark. The rotor design approach is based on Euler’s turbomachinery equation, ensuring consistency with angular momentum conservation principles. The integration of a duct allows for a reduction in turbine diameter for a given power output, potentially enhancing structural durability and reducing system costs. Overall, the proposed analytical framework and design methodology provide a structured basis for evaluating and optimizing the performance of bidirectional ducted tidal turbines.

Maximum power coefficient of dual-rotor wind turbines: An improved momentum theory analysis on geometric configurations

As the world's largest electricity consumer, China has long faced a shortage of publicly available electricity load data at a high temporal resolution. To address this limitation, this study leverages the strong correlation between electricity demand and meteorological conditions, as well as the broad accessibility of hourly weather data. By combining the limited publicly released load statistics from the National Development and Reform Commission with detailed hourly observations of temperature, wind speed, solar irradiance, and relative humidity, we estimated province-level power coefficients and threshold temperatures for both cooling and heating. These coefficients were then used to reconstruct hourly electricity load profiles for all provinces. The resulting dataset provides hourly electricity demand for 31 provincial-level regions across China for the period 2015-2024. Importantly, the proposed methodology is highly scalable and can be extended to any target year using annual electricity consumption data, air conditioner ownership per household, and corresponding hourly meteorological inputs. This dataset offers a valuable empirical foundation for research on electricity demand dynamics and long-term energy system planning in China.

This paper outlines an approach for carrying out a linear stability analysis of spatial xenon-induced power oscillations in a large pressurized heavy water reactor (PHWR) using the modal synthesis technique. The results obtained from the stability analysis are compared with those obtained by a solution using the improved quasi-static method. The present approach offers a computationally efficient linear stability assessment rather than obtaining the same using the improved quasi-static approach. In this approach, the space-time–dependent neutron flux is expressed as a product of the time-dependent amplitude function and the space-dependent eigenfunctions known as modes. This technique is used to solve time-dependent neutron diffusion equations, incorporating delayed neutrons, iodine, and xenon feedback effects. An eigenvalue-based linear stability analysis is performed for the first three harmonic modes, considered one at a time. Stability boundaries are generated in the parameter space defined by the operating power fraction and the power coefficient of reactivity, identifying both the stable and unstable regimes. Numerical simulations validated the stability boundary, showing growing, sinusoidal, and damped oscillations in the unstable boundary and stable regions, respectively. The model is verified against the space-time neutronics code IQS-3D, which uses the improved quasi-static method for the solution to the top-to-bottom and side-to-side modes for different operating power levels. The results indicated a stability threshold of ~46% full power (FP) for nominal reactivity device configurations, with some configurations stabilizing the xenon oscillations even at 100%FP. These findings highlight the key role of xenon dynamics in the determination of reactor stability and present a computationally efficient tool for mapping the operational stability boundaries in PHWRs. This model can be further used to perform nonlinear stability analyses.

Avian wings enable autonomous control over flight trajectory and speed, and their swept-wing geometry inspires the application of sweep modifications to horizontal-axis wind turbine blades, an approach that is critical for improving aerodynamic performance. Hence, wind tunnel experiments were performed to evaluate the output power and wake features of a baseline straight-bladed and a swept-blade wind turbine. The experimental results demonstrate that inflow turbulence intensity (T.I.) affects the peak power coefficient of the swept-bladed turbine, with power coefficient gains being more significant when the tip speed ratio is greater than 3.0 and under yawed conditions. At a yaw angle of 20°, when the T.I. is 0.5%, 10.5%, and 19.0%, respectively, the corresponding increased values are 13.17%, 3.44%, and 4.68%. Cross-stream velocity in the near-wake region of the swept-bladed turbine is markedly higher than that for the baseline condition. The averaged T.I. in the wake velocity region of the swept-blade conditions is greater than that of the baseline condition at most measurement positions. Moreover, power spectral density (PSD) magnitudes behind the blade tip for the swept-blade configuration are higher than those of the baseline, particularly in the medium- and high-frequency domains. This work clarifies the aerodynamic characteristics of swept-blade wind turbines to varying levels of turbulent inflow.

Acoustic requirement of wind turbines can be efficiently meted using optimal design methods, which balance aerodynamic and acoustic goals. Yet, considering an additional discipline in optimization drastically increases the total cost. This paper proposes a cost-effective design optimization approach based on enhanced methods for both formulation and solution. Therefore, the problem is formulated using the MASSOUD deformation-based method, and then solved based on the cost-effective meta-models. The latter are constructed using an improved radial basis function (RBF) and an adaptive sampling, which is generated starting with a Latin hypercube database and enriched iteratively based on an exploration/exploitation criterion. The evaluation of the database is achieved by the validated aero-acoustics (CFD-CAA) simulations. The trained meta-model is coupled with the multi-objective algorithm NSGA-II in order to maximize the power coefficient and reduce the generated noise. The results show a maximum increase of 22% in the power coefficient at a tip speed ratio of 3.2. A consistent attenuation of higher-order tonal components is observed for all optimized configurations, with significant reductions at the second and third harmonics Moreover, the acoustic outcomes exhibit strong directional dependency. Noise reduction is observed in the upstream rotor region, accompanied by increased noise levels in the downstream zone. These findings are supported by detailed flow field analyses, which reveal the mechanisms governing aero-acoustics behavior.

Accurate aerodynamic performance prediction and blade geometry optimization are critical for enhancing wind turbine energy efficiency. This study establishes a Blade Element Momentum (BEM) simulation framework for a wind turbine, focusing on the impacts of correction models, blade parameterization methods, and operating parameters on rotor performance. The results demonstrate that uncorrected ideal Betz models severely overestimate power coefficients, while Prandtl/Glauert corrections yield physically realistic predictions, confirming their necessity in BEM simulations. Comparative analysis reveals that the Bézier curve parameterization achieves a peak power coefficient of 0.4762, significantly outperforming the polynomial method, and is thus selected for blade geometry definition. Further investigation quantifies the combined effects of pitch angle and tip speed ratio, showing that moderate pitch angles optimize aerodynamic loading across operating ranges. Finally, the wind turbine power curve from 4 to 12 m/s is derived, validating the high efficiency of the optimized design. This work provides a systematic reference for wind turbine rotor design and performance evaluation.

Experimental study on flexible and rigid 3D-Printed Savonius vertical axis wind turbines with aerodynamic augmentation

The article discusses the method of hurricane sample replacement taking into account the spatial relationship of other routine samples. This sample is presented as the result of selecting sampling parameters with the mineral content above average values determined using the proposed methodology. The approach is based on geostatistical findings regarding the spatial dependence of sampled subsurface areas within a single geological block. The feature of the proposed methodology is the calculation of the studied indicator taking into account all samples for the evaluated block including the hurricane one. The approach is based on the method for determining weighting coefficients from the inverse distance weighted method. The method has been tested using the exploration data from a placer gold deposit. All key parameters of the proposed method, such as the radius and number of additional points created, as well as the power coefficient of the weighting function are analyzed. Several indicators are identified that will influence the results of mineral reserves calculations taking into account a hurricane sample and when it is replaced by the values calculated using the proposed methodology. The article analyses a situation in which the study object is selected incorrectly. It is demonstrated how the replacement of an outlier value can affect the assessment results for a given geological block. Examples of replacing similar samples are provided along with the assessment of the impact on the change in estimated reserves for a placer gold deposit. A conclusion is drawn regarding the error in determining the hurricane sample with the comparison of the impact on the exploration results and geological block assessment. The article is based on the study of a geological block tested by vertical boreholes, in which the gold content was determined. The results were obtained by modeling the process of determining the values to be used to replace the selected sample. The conducted analysis shows the effect of volume changes for various parameter variants of the proposed method. The article is illustrated with grade-interpolated plots and graphs showing curves for various parameters of calculated indicators.

Micro-scale counter-rotating wind turbines (CRWTs) offer enhanced potential for wake energy recovery. This study proposes an integrated cascade–coupling design framework for high-solidity CRWTs, in which rear rotor geometry and rotor coupling are co-designed based on stereoscopic particle image velocimetry measurements of the front rotor wake. Experiments are conducted at a tip-speed ratio of λ=1.0, solidity σ=1.25, spacing ratios of d=0.6RT, 1.0RT, and 3.0RT, and a tip radius of RT=70 mm. At the physical limit spacing of d=0.6RT, the integrated design increases the system power coefficient by 24.1% while limiting front rotor power reduction to 17.2%, compared to a 10.3% system gain and 34.5% front rotor suppression for the baseline mirrored configuration. Wake measurements confirm near-complete absorption of rotational kinetic energy from the front rotor wake without exacerbating upstream interference. These results demonstrate that cascade-based energy extraction and coupling-based interference mitigation can operate synergistically, enabling compact, high-performance micro-scale CRWTs suitable for space-constrained and urban energy applications.

Global decarbonisation requires efficient and reliable renewable energy systems, with Vertical Axis Wind Turbines ( VAWTs ) offering advantages in turbulent and urban environments. This study examines the effect of blade Fixing Angle ( FA ) on the aerodynamic performance of a three-bladed Darrieus VAWT using Unsteady Reynolds-Averaged Navier–Stokes ( URANS ) based Computational Fluid Dynamics ( CFD ) simulations coupled with an Artificial Neural Network ( ANN ) surrogate model. A parametric analysis was carried out for seven FA values across a Tip-Speed Ratio ( TSR ) range of 0.5 − 3.0 . Results show that a small positive FA (toe-out) improves efficiency by delaying stall onset and extending upwind torque production. The optimum case ( FA = + 1.5 ∘ , TSR = 2.0 ) achieved a 15.3 % increase in power coefficient ( C P ) compared to the baseline ( FA = 0 ∘ , TSR = 2.0 ) . In contrast, negative FA reduced performance due to earlier separation and greater downwind losses. The ANN surrogate, trained on CFD data, effectively captured the nonlinear dependence of C P on TSR and FA , achieving R 2 = 0.98 and a Mean Absolute Error ( MAE ) below 0.01 . Once validated, the ANN enabled rapid optimisation of the design space, locating the global optimum with negligible computational cost. Flow-field and force-coefficient analyses further reveal that positive FA modifies the incidence-angle distribution, mitigates torque ripple, and suppresses dynamic stall, thereby explaining the observed performance enhancement. Overall, the integration of CFD and ANN provides both physical insight and computational efficiency, establishing a solid foundation for future multi-objective optimisation of VAWTs considering parameters such as C P , torque ripple, and self-starting capability.

Energy crisis due to fast globalization and the negative effects of global warming compels a greater need for nonconventional energy sources. Solar and wind power are the primary sources of renewable energy used to meet the power demand. Savonius rotor, a kind of vertical-axis wind turbine, whose operation is dependent upon drag force, has many benefits, including low operating speeds, good self-starting ability, ease of installation, design simplicity, and wind direction independence. However, the low efficiency of the turbine caused by the negative torque it produces on the returning blade limits the applicability of the turbine. The present work experimentally investigated the possibility of performance improvement of the turbine by incorporating inner blades. A 3-bladed configuration of the turbine containing 2 inner blades and an outer semi-circular blade was designed and constructed for performance assessment using an open circuit wind tunnel. Three turbine configurations with 160º inner blade angle and 2 cm spacing between the blades were tested for optimal performance. The performance was evaluated for different wind velocities by fixing the test setup at the wind tunnel outlet. The rotational speed and torque were measured using a rope break dynamometer and tachometer, respectively. The result indicated that using 1 inner arc blade improved the maximum power coefficient and torque coefficient of the rotor by 33.17% and 8.89%, respectively, compared to the conventional configuration. However, using 2 inner blades reduced the maximum power coefficient and torque coefficient by 37.43% and 46.67%, respectively. The maximum value of the power coefficient was found at tip speed ratios (TSRs) between 0.25 and 0.45, whereas the torque coefficient declined with the increase of TSR for all 3 configurations. Moreover, the maximum power coefficient and torque were observed at lower wind speeds.

Parametric analysis and optimization of lift-type vertical axis wind turbines using machine learning techniques