Small-scale Wind Research Articles

Small-scale wind fluctuations within melting layers of winter storms: results from WINTRE-MIX

Abstract Investigations into the melting layer (ML) of winter storms have revealed small-scale fluctuations in the horizontal wind that could significantly affect surface precipitation type and the evolution of the ML. Despite previous evidence of such fluctuations, essential questions remain concerning their characteristics and the forces driving them. Therefore, this study characterizes small-scale horizontal wind fluctuations (<1 km in length with perturbation magnitudes < 3 m s−1) and their environments within the ML of winter storms. This analysis uses data from a scanning X-band Doppler radar collected during the Winter Precipitation Type Research Multi-Scale Experiment (WINTRE-MIX), conducted during February and March 2022. We present three case studies where small-scale horizontal wind fluctuations are identified using along-radial and along-azimuthal radial velocity perturbations. These cases cover the range of environmental conditions observed during WINTRE-MIX, including: i) a descending ML with change in surface p-type from snow to rain, ii) a steady ML with a surface p-type transition from freezing rain to rain due to surface cold air erosion, and iii) a steady ML with a surface p-type transition from freezing rain to ice pellets due to surface cold air advection. Forcing mechanisms for small-scale wind fluctuations during each case are attributed to static instability, vertically trapped gravity waves, and/or shear instability inferred from rawinsonde data, HRRR analysis, and radar data. Our findings suggest that static instability, gravity waves, and shear instability drive the ML’s small-scale wind fluctuations and may influence surface precipitation-type transitions.

Experimental and numerical analysis of NREL S823 airfoil with auxiliary airfoil integration

ABSTRACT This study explores the potential for using an auxiliary airfoil to improve the aerodynamic characteristics of an NREL (National Renewable Energy Laboratory) S823 airfoil designed explicitly for small-scale wind turbines. The experimental investigation is carried out on a standard S823 airfoil (S823(S)) and an S823 with the inclusion of an auxiliary airfoil (S823(A)), at different angles of attacks (0º-20º) and different low wind speeds (4–10 m/s). The result shows that the S823(A) model consistently outperforms the S823(S) model in terms of lift-related metrics. It exhibited a 10% increase in CL values. Specifically, the S823(A) model achieved a maximum CL value of 1.284 at 10 m/s, which is an 8% improvement over the S823(S) model’s maximum of 1.191 at the same wind speed. Besides, the S823(A) model demonstrated superior performance in the sliding ratio, with values consistently higher by approximately 11%, 9%, 10%, and 14% at wind speeds of 4 m/s, 6 m/s, 8 m/s, and 10 m/s, respectively. Moreover, numerical simulations were carried out for both the models at similar conditions, which reveal that using an auxiliary airfoil reduces flow separation on the pressure side, along with well controlling the Turbulence Kinetic Energy (TKE) dissipation of the S823(A) model. Moreover, the airfoil flow visualization reveals that the auxiliary airfoil promotes smoother airflow separation, especially near the trailing edge of the airfoil. This reduces turbulence and improves the overall stability and controllability of the airfoil across different AoAs. Overall, the S823(A) model offers superior aerodynamic performance, improved lift-to-drag ratio, and better control characteristics across a range of angles of attack compared to the S823(S) model that improves the overall aerodynamic performance of the main airfoil.

A New Stochastic Controller for Efficient Power Extraction from Small-Scale Wind Energy Conversion Systems under Random Load Consumption

This paper presents an innovative scheme to enhance the efficiency of power extraction from wind energy conversion systems (WECSs) under random loads. The study investigates how stochastic load consumption, modeled and predicted using a Markov chain process, impacts WECS efficiency. The suggested approach regulates the rectifier voltage rather than the rotor speed, making it a sensorless and reliable method for small-scale WECSs. Nonlinear WECS dynamics are represented using Takagi–Sugeno (TS) fuzzy modeling. Furthermore, the closed-loop system’s stochastic stability and recursive feasibility are guaranteed regardless of random load changes. The performance of the suggested controller is compared with the traditional perturb-and-observe (P&O) algorithm under varying wind speeds and random load variations. Simulation results show that the proposed approach outperforms the traditional P&O algorithm, demonstrating higher tracking efficiency, rapid convergence to the maximum power point (MPP), reduced steady-state oscillations, and lower error indices. Enhancing WECS efficiency under unpredictable load conditions is the primary contribution, with simulation results indicating that the tracking efficiency increases to 99.93%.

Determination of unsteady wing loading using tuft visualization

Unsteady separated flow affects the aerodynamic performance of many large-scale objects, posing challenges for accurate assessment through low-fidelity simulations. Full-scale wind tunnel testing is often impractical due to the object’s physical scale. Small-scale wind tunnel tests can approximate the aerodynamic loading, with tufts providing qualitative validation of surface flow patterns. This investigation demonstrates that tufts can quantitatively estimate unsteady integral aerodynamic lift and pitching moment loading on a wing. We present computational and experimental data for a NACA0012 wing, capturing unsteady surface flow and force coefficients beyond stall. Computational data for varying angles of attack and Reynolds numbers contain the lift coefficient and surface flow. Experimental data, including lift and moment coefficients for a tuft-equipped NACA0012 wing, were obtained at multiple angles of attack and constant Reynolds number. Our results show that a data-driven surrogate model can predict lift and pitching moment fluctuations from visual tuft observations.

Optimization of a hybrid renewable energy system for off-grid residential communities using numerical simulation, response surface methodology, and life cycle assessment

This paper presents an optimized hybrid renewable energy system tailored for off-grid residential communities, integrating wind, solar, and hydrogen technologies to meet electricity, cooling, heating, and water needs. The proposed optimization methodology combines numerical simulation, response surface methodology (RSM), and life cycle assessment (LCA), ensuring robust performance across diverse conditions. Key components include fuel cells, reverse osmosis systems, heat pumps, photovoltaic/thermal solar collectors, wind turbines, and hydrogen generation systems. The optimization process targets critical variables such as PVT panel area, the number of wind turbines, and fuel cell power. The optimal configuration was found to include 24 small-scale wind turbines, 159.46 m2 of PVT collectors, and 79.73 kW of fuel cell power. This configuration generated surplus electricity with net electricity usage (NEU) values of −123084.27 kWh/year in New York, −224245.29 kWh/year in Forks, and −215949.30 kWh/year in Santa Barbara. Additionally, the optimized systems achieved a significant reduction in life cycle cost (LCC), with Forks showing the lowest LCC at 304428.97 USD. The environmental impact was also minimized using the novel optimization approach, with the optimized systems achieving negative 100-year global warming potential (GWP100) values, indicating a net reduction in greenhouse gas emissions.

MPPT Optimal Torque Control Strategy for a PMSG-based Wind Turbine Emulator

A wind turbine emulator is a valuable tool, which enables real-time physical simulation of a wind turbine behavior using a dedicated experimental test setup, providing a controlled environment for research and development purposes. One significant advantage of using this tool is its ability to test control algorithms designed to maximize power extraction from the wind turbine. This paper continues previous work on developing a small-scale variable-speed wind turbine emulator based on a Permanent Magnet Synchronous Generator for stand-alone applications (Benhacine et al., 2024). This paper presents enhancements made to the emulator. These improvements facilitate the assessment of a maximum power point tracking control strategy designed to optimize power extraction from the wind turbine.

Numerical investigation of turbulent flow over a small-scale vertical axis wind turbine

The present paper aims to analyse the aerodynamics of turbulent fluid flow over a vertical axis wind turbine (VAWT). A 2D study is carried out for a two-bladed SAVONIUS wind turbine, where the rotor diameter is D=20cm. The governing equations (Unsteady Reynolds Averaged Navier Stokes URANS) are solved numerically using a CFD (computational fluid dynamics) open-source code based on the finite volume method; the SST turbulence model is applied for the system closure. An arbitrary mesh interface (AMI) technique is applied at the sliding interface boundary, which is a circular surface separating between the rotating zone and the fixed zone where the mesh remains stationary. The numerical results allow predicting the vorticity and pressure distributions over a rotating wind turbine for different tip speed ratios in order to characterize the generated wake. The velocity deficit is calculated for different positions behind the rotor to characterize the disturbance rate of the flow.

Pressure loss and droplet entrainment under spray absorber conditions

The interaction of spray with counter-flowing flue gas causes pressure loss (ΔP) and influences droplet entrainment and sorbent loss in gas–liquid scrubbers. As these phenomena were usually investigated separately and not linked with atomizer characteristics, it is difficult to obtain insight into the scrubber operation and select an atomization device proper to particular process. Atomizers typically used in a spray column, together with pressure-swirl and twin fluid effervescent types, were tested in column-like conditions. All the atomizers were tested at the same liquid flow rate of 140 kg/h, with inlet pressure (pin) from 0.025 to 0.2 MPa under the counter–flow velocity (ucf) ranging from 0to1 m/s. A small-scale low-speed wind tunnel was specially designed to simulate spray column flow conditions. The ΔP and droplet entrainment were correlated with atomizer operating regimes. Empirical and analytical models of ΔP were compared with experimental results for different atomizers. Limitations of both models are discussed. The ΔP is influenced by the spray velocity at the discharge orifice (uL) and correlates well with the liquid kinetic energy (Ek) and Reynolds number at the discharge orifice. The atomizers working on higher pin, provide a larger interfacial area, but yield higher Ek at the discharge orifice, causing larger ΔP and a greater risk of sorbent loss due to presence of smaller droplets.

Determining Payback Period and Comparing Two Small-Scale Vertical Axis Wind Turbines Installed at the Top of Residential Buildings

In recent years, residential buildings have seen a notable increase in energy consumption. To address this, it is crucial for researchers to invest in renewable energy technologies, aiming to develop highly sustainable and nearly-zero energy buildings. Many countries are started to commit to this goal, seeking to phase out fossil fuels due to their harmful environmental effects. Wind energy stands out as a promising renewable resource, especially in areas with strong wind patterns. This study focuses on a case in Karaburun, Izmir province, Türkiye, where annual wind speeds range from 6 to 8 m/s and evaluates the performance of two types of small-scale Vertical Axis Wind Turbines (VAWTs) in reducing energy consumption in a three-story residential building, along with associated costs. Utilizing advanced simulation tools like ANSYS Fluent and DesignBuilder Software, the study examines Ice-Wind VAWTs and Savonius VAWTs. The findings reveal that installing 15 Ice-Wind VAWTs on the building's roof can reduce energy consumption by approximately 22.5%, with each turbine costing about $2000 and a payback period of around 14.57 years. Conversely, using 15 Savonius VAWTs can reduce energy consumption by 36%, with each turbine costing about $2300 and a payback period of around 8.93 years. These results indicate that the Savonius turbine offers a faster return on investment compared to the Ice-Wind turbine under the specified conditions. Overall, this study highlights the significant benefits and cost implications of integrating renewable energy solutions like VAWTs into residential buildings.

Aerodynamic analysis of a small-scale Savonius wind turbine incorporated with wind lenses: A CFD approach for wake pattern and power prediction

Aerodynamic analysis of a small-scale Savonius wind turbine incorporated with wind lenses: A CFD approach for wake pattern and power prediction

Study on novel control method for small wind – solar hybrid power system using photovoltaic cooperating system in parallel connection mode

Currently, a small-scale wind turbine can be connected to the Power Conditioning System (PCS) of the solar power system by simulating the technical characteristics of the solar panels to enhance the efficiency of the PCS on cloudy or rainy weather days. However, the working efficiency of the entire system has not been optimized because the use of traditional control techniques. P-I control has several problems of high starting overshoot, and slow response to sudden disturbances. Besides, P&O MPPT control has fluctuations in output power and slow response time at peak solar cell power due to weather effects. Therefore, this research proposes a novel control system including Artificial Neural Networks (ANN) MPPT control and digital slide mode control (DMSC) for the power conversion circuit to connect small-scale wind turbine power with the PCS of the solar power system in the parallel mode. The novel control solution in this study can minimize the disadvantages of PI control and P&O MPPT control. The study results showed that DSMC controller has better performance than the PI controller when controlling the PVCS in parallel mode with more 17.5 % power, no static error, 20 % less chattering of the power value of PVCS in the steady state, and 20 % less static error of power. Besides, the ANN MPPT controller also works better when changing solar radiation and has a harvested power of about 0.6 % higher than the power generated by the P&O MPPT controller.

Experiment research on the characteristics and mechanism of noise caused by a car door sealing cavity at wind excitation

Due to the various geometric shapes of cavities within car door sealing systems, the resulting cavity noise induced by wind excitation exhibits complex characteristics, leading to unclear noise mechanisms. To address this, a study was conducted to examine the acoustic properties of door sealing cavities located in the B-pillar, C-pillar, and backdoor of an SUV within a full-scale aeroacoustic wind tunnel. The main objective was to explore the relationship between cavity noise and interior noise. The results showed that peak components in the sound pressure level spectrum of the cavities significantly contribute to interior noise, particularly for cavities located close to the car’s interior. To gain further insight, the geometric characteristics of the cavities were extracted and transformed into equivalent regular cavities. These equivalent cavities were subsequently tested for their noise performance in a small-scale aeroacoustic wind tunnel, and the occurrence mechanisms were thoroughly investigated. The results demonstrated that the noise spectra of different cavities, whether they had sealing strips or leakage gaps, exhibited typical multipeak characteristics, with some cases even leading to whistling (e.g. backdoor cavity). The reason for the whistling was a resonance when the self-sustained oscillation frequencies of the cavities coincided with or approached the Helmholtz resonance frequencies or modal frequencies of the cavities. Interestingly, the self-sustained oscillation frequency and cavity modal resonance still persisted even when the two frequencies were somewhat separated, albeit with peaks of lower magnitude in the sound pressure spectrum (e.g. in the sealed cavities of the B-pillar and C-pillar).

Comparative Analysis of Estimated Small Wind Energy Using Different Probability Distributions in a Desert City in Northwestern México

In this paper, four probability functions are compared with the purpose of establishing a methodology to improve the accuracy of wind energy estimations in a desert city in Northwestern Mexico. Three time series of wind speed data corresponding to 2017, 2018, and 2019 were used for statistical modeling. These series were recorded with a sonic anemometer at a sampling frequency of 10 Hz. Analyses based on these data were performed at different stationarity periods (5, 30, 60, and 600 s). The estimation of the parameters characterizing the probability density functions (PDFs) was carried out using different methods; the statistical models were evaluated by the coefficient of determination and Nash–Sutcliffe efficiency coefficient, and their accuracy was estimated by the measured quadratic error, mean square error, mean absolute error, and mean absolute percentage error. Weibull, using the energy pattern factor method, and Gamma, using the Method of Moments, were the probability density functions that best described the statistical behavior of wind speed and were better at estimating the generated energy. We conclude that the proposed methodology will increase the confidence of both wind speed estimation and the energy supplied by small-scale wind installations.

Reconstructing Energy-Efficient Buildings after a Major Earthquake in Hatay, Türkiye

Türkiye’s earthquake zone, primarily located along the North Anatolian Fault, is one of the world’s most seismically active regions, frequently experiencing devastating earthquakes, such as the one in Hatay in 2023. Therefore, reconstructing energy-efficient buildings after major earthquakes enhances disaster resilience and promotes energy efficiency through retrofitting, renovation, or demolition and reconstruction. To this end, this study proposes implementing energy-efficient design solutions in dwelling units to minimize energy consumption in new buildings in Hatay, Southern Turkiye, an area affected by the 2023 earthquake. This research focused on a five-story residential building in the district of Kurtlusarımazı, incorporating small-scale Vertical-Axis Wind Turbines (VAWTs) with thin-film photovoltaic (PV) panels, along with the application of a green wall surrounding the building. ANSYS Fluent v.R2 Software was used for a numerical investigation of the small-scale IceWind turbine, and DesignBuilder Software v.6.1.0.006 was employed to simulate the baseline model and three energy-efficient design strategies. The results demonstrated that small-scale VAWTs, PV panels, and the application of a green wall reduced overall energy use by 8.5%, 18%, and 4.1%, respectively. When all strategies were combined, total energy consumption was reduced by up to 28.5%. The results of this study could guide designers in constructing innovative energy-efficient buildings following extensive demolition such as during the 2023 earthquake in Hatay, Türkiye.

Effect of rotation on achieving constant voltage in three-phase self-excited induction generator for small scale wind turbines application

Three-phase Self-Excited Induction Generators (SEIGs) are commonly employed for electricity generation in remote or isolated areas. SEIGs are preferred in such regions due to their ability to create a magnetic field by adding a capacitor to one of their terminals. Nevertheless, a significant challenge in utilizing SEIGs is maintaining a consistent output voltage in the presence of load fluctuations. This study aims to investigate the impact of generator rotation on the SEIG's output voltage and determine the optimal rotation speed required for achieving a stable output voltage. Ensuring stable voltage regulation is crucial to guarantee the proper functioning of all loads connected to the SEIG. Furthermore, operating the SEIG in parallel with other generators is advantageous. The methodology employed in this study involves varying the load supplied by the SEIG at different capacitor values. Unwanted voltage variations occur due to load fluctuations within a generating system or SEIG. Adjustments to the generator's rotation speed are made to uphold a uniform voltage level. The variables considered in this study include the generator's rotation speed, capacitor size, and load fluctuations. Simulation results demonstrate that the SEIG's output voltage is affected by the generator's rotation speed, and maintaining a consistent voltage necessitates appropriate adjustments to capacitor values and generator speed. This research enhances understanding of SEIG characteristics and offers guidance on effective settings for maintaining a stable output voltage at various generator rotation speeds. Future research can focus on practically implementing these findings to enhance the performance of SEIGs in real-world applications

Performance Analysis of Permanent Magnet Synchronous Generator for Small Scale Wind Energy Applications

This paper presents a study of the performances of a permanent magnet synchronous generator (PMSG) used in small scale wind energy applications. The d-q model is adopted for the performance analysis of the PMSG under variable operating conditions. In addition, in order to validate the results obtained with the theoretical model, an experimental test bench based on a small PMSG equipped with a data acquisition system has been developed. The study carried out on the experimental test bench made it possible to determine both the dynamic and the steady state performances of the PMSG under variable loads and rotational speeds.

The Effect of Nacelle Shape and Blade Geometry on the Performance of Small Scale Wind Turbine

The Effect of Nacelle Shape and Blade Geometry on the Performance of Small Scale Wind Turbine

Commercial Small-Scale Horizontal and Vertical Wind Turbines: A Comprehensive Review of Geometry, Materials, Costs and Performance

The effective exploitation of renewable energy sources is one of the most effective solutions to counter the energy, environmental and economic problems associated with the use of fossil fuels. Small-scale wind turbines (converting wind energy into electric energy with a power output lower than 50 kW) have received tremendous attention over the past few decades thanks to their reduced environmental impact, high efficiency, low maintenance cost, high reliability, wide wind operation range, self-starting capability at low wind speed, limited installation space, reduced dependence on grid-connected power and long transmission lines, low capital costs, as well as the possibility to be installed in some urban settings. However, there are significant challenges and drawbacks associated with this technology from many different perspectives, including the significant discrepancy between theoretical performance data provided by the manufacturers and real field operation, that need to be investigated in greater depth in order to enable a more widespread deployment of small-scale wind turbines. In this review, a complete and updated list of more than 200 commercially available small-scale horizontal and vertical wind turbine models is provided and analysed, detailing the corresponding characteristics in terms of the number and material of blades, start-up wind speed, cut-in wind speed, cut-out wind speed, survival wind speed, maximum power, noise level, rotor diameter, turbine length, tower height, and specific capital cost. In addition, several scientific papers focusing on the experimental assessment of field performance of commercially available small-scale horizontal and vertical wind turbines have been reviewed and the corresponding measured data have been compared with the rated performance derived from the manufacturers’ datasheets in order to underline the discrepancies. This review represents an opportunity for the scientific community to have a clear and up-to-date picture of small-scale horizontal as well as vertical wind turbines on the market today, with a precise summary of their geometric, performance, and economic characteristics, which can enable a more accurate and informed choice of the wind turbine to be used depending on the application. It also describes the differences between theoretical and in-situ performance, emphasizing the need for further experimental research and highlighting the direction in which future studies should be directed for more efficient design and use of building-integrated small-scale wind turbines.

Onsite measurements of pedestrian-level wind and preliminary assessment of effects of turbulence characteristics on human body convective heat transfer

Wind is an important factor affecting outdoor thermal comfort in urban environment, but its turbulence characteristics at the pedestrian level and effects on convective heat transfer (hc) from a human body remain poorly understood. Previous studies were only conducted in wind tunnels with low turbulence intensity, small turbulence integral length scale, and fixed prevailing wind direction. To address this knowledge gap, this field study was conceived to monitor the pedestrian level wind in actual outdoor settings and to measure the hc of a thermal manikin at the same time. The results show that both longitudinal and lateral turbulence intensity significantly enhance whole body hc. It remains to be examined whether the small-scale wind direction variation can be included in the lateral turbulence intensity or vice versa. The integral length scale found at the two sites were larger than a typical manikin dimension, and the whole body hc peaked when these two scales were comparable. As the first major field study to quantify convection heat loss of a thermal manikin exposed to real-life urban boundary layer wind, it is demonstrated crucial to consider realistic turbulence characteristics in the field when evaluating hc over a human body for urban microclimate design.

Fluid-structure interaction and life prediction of small-scale damaged horizontal axis wind turbine blades

Throughout their operational lifespan and exposure to various environmental conditions, wind turbines experience diverse loading scenarios that could lead to blade cracking, affecting their structural integrity. This research focuses on analyzing the blade lifespan of two small-scale wind turbines, namely Air Silent X and Pikasola. The investigation introduces deliberate irregularities like holes, erosion, and cracks to examine their effects on blade durability. Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) are used to assess aerodynamic loads, deflection, and stress levels on the blades under different wind speeds. Leveraging the fracture analysis tool within ANSYS, the study predicts blade lifespan in terms of cycles. The findings revealed that anomalies located near high-stress regions tend to reduce the lifespan of blades compared to those positioned in lower-stress areas.