Small-scale Wind Turbine Research Articles

Numerical visualization of wind turbine wakes using passive scalar advection–diffusion equation and its application for wake management

To visualize and characterize the unsteady properties of the wake trailing behind a wind turbine, we propose a novel numerical methodology in this study. Through a wind-tunnel experiment using a smoke generator, we succeeded in visualizing a compact-type small-scale wind turbine wake using continuous scalar plumes from a single point source. Next, to simulate the above wind-tunnel experiment, we proposed a method using the passive scalar advection–diffusion equation based on a high-fidelity large-eddy simulation (LES). The actuator-line method (ALM) was adopted for the wind turbine model. We succeeded in qualitatively reproducing the wake visualization experiment in the wind tunnel described above and verified the effectiveness of the proposed numerical visualization method. To evaluate the characteristics of wakes generated by wind turbines in more detail, we conducted a quantitative comparison using a disk-shaped volume source with the same size as the swept area, set behind the wind turbine model. The results indicated that the non-dimensional time-averaged passive scalar profile in the near- and far-wake regions qualitatively matched the shape of the stream-wise velocity profile, despite having opposite signs. In other words, it was shown that if a disk-shaped volume source with the same size as the swept area is placed just behind the wind turbine, it is possible to accurately predict the behavior of the wind turbine wake. Finally, to validate the proposed method for wind farm wake management, we performed a visualization of wake flows in a virtual offshore wind farm consisting of 12 wind turbines with short separation distances. Through detailed comparison of two types of numerical results with different wind directions, we showed that the proposed method can effectively demonstrate the range of spatial influence of the wakes formed by the wind turbine with special attention.

MPPT FOR HYBRID WIND, SOLAR AND THERMOELECTRIC POWER GENERATION SYSTEMS FOR OFF-GRID APPLICATIONS

Renewable energy resources for electrical generation are normally free but are not continuously available due to their sporadic availability. Thus, hybrid connections of various kinds of energy are made to increase utilization of renew-able energy. This paper involves a design of a hybrid renewable energy system employing maximum power point tracking (MPPT) techniques. The hybrid system consists of solar PV panels, a small-scale wind turbine, and a thermoelec-tric generator (TEG) module. Four MPPT techniques are examined in this research. They are the incremental conductance (IC) algorithm, fuzzy logic controllers (FLC) using 25 and 35 rules, and an interval type 2 fuzzy logic con-troller (IT2FLC). Each MPPT technique is tested in the system to determine which has the best maximum power tracking, stable operation, and efficiency. All of the studied energy resources are connected to a DC linked bus. The voltage of this bus is supplied to a three-phase inverter. Inverter output voltage is regulated for balanced and unba¬lanced loads. The generating capacity of the designed hybrid system is 5 kW and the system is simulated using MATLAB Simulink R2017a.

Cloud-Based Energy Storage Systems: A shared pool of benefits in distributed electric power systems

Social, environmental, and economic motivations, along with disruptive technological advancements, have been leading to substantial changes in the landscape of the energy supply chain. The progress in sensor fusion, readiness of remote and interactive controllers and actuators, abundance of low-cost and highly available communication media, proliferation of distributed energy resources (DERs), and maturity of monitoring devices and control algorithms have fostered the concept of distributed electric power systems. Plug-and-play capability, along with ever-declining capital costs and the economic breakeven of small-scale photovoltaic (PV) panels and wind turbines, has enabled retail customers located at the low-voltage end of feeders to have access to abundant and variable energy resources in their territories.

Application of M-SWARA and TOPSIS Methods in the Evaluation of Investment Alternatives of Microgeneration Energy Technologies

Investments in microgeneration technologies help to boost the usage of clean energy while reducing pollution. However, selecting the appropriate investment remains the most critical phase in developing these technologies. This study aims to design a multi-criteria decision-making method (MCDM) to evaluate investment alternatives for microgeneration energy technologies. The proposed MCDM is based on a Multi Stepwise Weight Assessment Ratio Analysis (M-SWARA), to define the relative importance of the factors. The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and q-Rung Orthopair Fuzzy Soft Sets (q-ROFSs) are used to rank investment alternatives. Calculations were also made with Intuitionistic Fuzzy Sets (IFSs) and Pythagorean Fuzzy Sets (PFSs). For analysis, five evaluation criteria were selected based on the literature: frequency of maintenance, ease of installation, environmental adaptation, transmission technologies, and efficiency of cost. Similarly, six alternatives for microgeneration technology investments were selected: ground source heat pumps, micro hydroelectric power, micro combined heat and power, micro bioelectrochemical fuel cell systems, small-scale wind turbines, and photovoltaic systems. The results showed that cost efficiency was the most significant factor in the effectiveness of microgeneration energy investments, and the photovoltaic system was the best alternative to increase microgeneration energy technology investment performance. Furthermore, the results were the same for the analyses made with IFSs and PFSs, demonstrating the reliability of the proposed method. Therefore, investors in microgeneration technologies should prioritize photovoltaic systems. This conclusion is supported by the fact that photovoltaic is a renewable energy source that has witnessed the most technological improvements and cost reductions over the last decade.

Optimal Design and Aerodynamic Performance Prediction of a Horizontal Axis Small-Scale Wind Turbine

The improved aerodynamic design of a horizontal axis small-scale wind turbine blade is crucial to increasing the efficiency and annual energy production of the turbine. One of the vital stages in aerodynamic design is the selection of the airfoil. Using the existing airfoils for a blade design which results in higher turbine characteristics is tedious. Consequently, this paper provides an optimal design strategy for a horizontal axis small-scale wind turbine blade through the multiobjective optimization of the airfoil using the Nondominated Sorting Genetic Algorithm II (NSGA-II). The latter outperforms the other commonly used genetic algorithms (GAs), as well as the Computational Fluid Dynamics (CFD) investigation of the different airfoil types and the wind turbine rotors on the steady or unsteady state aerodynamic performance. An NACA4412 airfoil with higher aerodynamic efficiency is considered as a baseline for the optimization in order to increase the lift coefficient and lift to drag ratio while avoiding excessive variations in the maximum relative thickness and area. The optimized airfoil (NACA4412-OPT) is used as the cross-sectional profile in the design procedure for a novel 1.15 m diameter three-bladed wind turbine rotor at a wind speed of 11.5 m/s, tip speed ratio of 4.65, and pitch angle of 0.2° by the Wilson design method. The two-dimensional analysis demonstrates that the optimized airfoil outperforms the other airfoils yielding the highest lift coefficient and lift to drag ratio, as well as a larger pitch range. The three-dimensional analysis shows that the time-averaged power coefficient value (0.33) of the new wind turbine is almost 26% higher and more stable than that of the original wind turbine while avoiding a high increase of the axial thrust.

Power and Energy Management of a DC Microgrid for a Renewable Curtailment Case Due to the Integration of a Small-Scale Wind Turbine

Economic dispatch optimization and power management are the main concerns for a microgrid (MG). They are always studied and are considered to achieve an efficient operation of the MG by simplifying the control process and decreasing losses. The integration of a small-scale wind turbine (SSWD) into a direct current (DC) MG has an impact on its power and energy management. Excess power produced by renewable energy sources (RESs) is one of the problems that face the reliability of the MG and should be resolved. For this reason, a supervisory system is suggested to manage the excess of power. During the supervision process, some criteria, such as the physical limits and tariffs of the components are taken into account. Then, the suggested power management strategy aims to achieve an instantaneous power balance considering a rule-based power and depends on the above-mentioned criteria. To better meet the power balance, it is necessary to explore the constraints related to the control and supervision of the studied DC MG. Performance measures include the overall system energy cost and renewable curtailment (renewable energy that cannot be utilized and should be limited). Thus, the power limitation strategy consists of using two types of “shedding coefficients”, α and γ, to calculate the power that should be limited from each RES in the case of energy surplus. Simulation tests are carried out using two power management strategies: optimization and without optimization (i.e., storage priority). The results reveal that the coefficient γ reduces the overall energy cost and whatever the applied coefficient, optimization still provides good performances and significantly reduces the global energy cost.

Aerodynamic Profile Modification of a NACA 0012 Aerofoil for Enhanced Lift-Drag Characteristics at Low Reynolds Number

This article discusses the enhanced lift-drag ratio of a geometrically modified National Advisory Committee for Aeronautics 0012 aerofoil at a low Reynolds number of 40000. The study involves validating the Reynolds Averaged Navier Stokes Transition Shear Stress Transport model for the analysis of flow around the subject aerofoil with the modified profile for angles of attack ranging from 0 to 10°. The coefficient of lift to drag increased by 70% for the modified aerofoil at an angle of attack of 6°. The extent of the laminar separation bubble on the modified airfoil is reduced by 40% compared to the standard aerofoil at an angle of attack of 8°. The modified aerofoil cross-section does not involve much manufacturing complexity and can be deployed in small-scale wind turbines operating at low wind speeds.

Design and Optimization of a Small-Scale Horizontal Axis Wind Turbine Blade for Energy Harvesting at Low Wind Profile Areas

Wind turbine blades perform the most important function in the wind energy conversion process. It plays the most vital role of absorbing the kinetic energy of the wind, and converting it to mechanical energy before it is transformed into electrical energy by generators. In this work, National Advisory Committee for Aeronautics (NACA) 4412 and SG6043 airfoils were selected to design a small horizontal axis variable speed wind turbine blade for harvesting efficient energy from low wind speed areas. Due to the low wind profile of the targeted area, a blade of one-meter radius was considered in this study. To attain the set objectives of fast starting time and generate more torque and power at low wind speeds, optimization was carryout by varying Reynolds numbers (Re) on tip speed ratios (TSR) values of 4, 5, and 6. The blade element momentum (BEM) method was developed in MATLAB programming code to iteratively find the best twist and chord distributions along the one-meter blade length for each Re and tip speed ratio (TSR) value. To further enhance the blade performance, the twist and chord distributions were transferred to Q-blade software, where simulations of the power coefficients (Cp) were performed and further optimized by varying the angles of attack. The highest power coefficients values of 0.42, 0.43, and 0.44 were recorded with NACA 4412 rotor blades, and 0.43, 0.44, and 0.45 with SG6043 rotor blades. At the Re of 3.0 × 105, the blades were able to harvest maximum power of 144.73 watts (W), 159.69 W, and 201.04 W with the NACA 4412 and 213.15 W, 226.44 W, 245.09 W with the SG6043 at the TSR of 4, 5, and 6 respectively. The lowest cut-in speed of 1.80 m/s and 1.70 m/s were achieved with NACA 4412 and SG6043 airfoils at TSR 4. At a low wind speed of 4 m/s, the blades were able to harness an efficient power of 79.3. W and 80.10 W with both rotor blades at the TSR 4 and 6 accordingly.

Development of a Dual-Input Magnetic Gear Train for the Transmission System of Small-Scale Wind Turbines

Magnetic gear mechanisms have advanced to have a promising future in transmission technology. Previous research indicates that magnetic gear mechanisms might replace mechanical gear mechanisms in some applications. Small-scale wind turbines (SWT) with counter-rotating rotors that were initially fitted by bevel gears are proposed to be replaced by a coaxial magnetic gear train (CMGT). The CMGT is intended for use as a speed multiplier in order to obtain maximum power at low wind speeds, due to its beneficial transmission of power without physical contact. The primary objective of this study is to build a dual-input CMGT that will be employed in the transmission system of small-scale counter-rotating wind turbines. A dual-input CMGT is built through the analytical modeling of an equivalent magnetic circuit (EMC), which aims to predict the magnetic flux density in the air-gaps of CMGT. Several models within design constraints were compared to obtain the optimum design parameters of the preliminary CMGT design resulting from an EMC analysis. The optimized critical design parameters were then selected and analyzed using finite-element analysis (FEA) to depict the performance of the proposed SWT design. According to the findings, the developed design can generate an inner air-gap flux density of 0.8314 T and an outer air-gap flux density of 1.0200 T. The model likewise produces promising simulation results with an output transmitted torque in the inner rotor (output link) of 8.7 Nm, 56.9 Nm in the outer rotor, and 48.0 Nm in the carrier with pole-pieces. Thus, this design can generate higher torque than a bevel-geared wind turbine. The speed characteristics are also compromised in order to raise the generator’s rotating speed to generate more power. Finally, this study demonstrates the performance and embodiment design of the proposed SWT using CMGT.

Current source gate drivers for 3-phase VSI operated in small-scale wind turbine systems

The paper is dedicated to the improvement of efficiency of small-scale wind turbines’ (SSWT) power electronic converters. An efficiency of the 3-phase voltage source inverter that operates with low output voltage (<60 V) and high grid-side input voltage (380 V) is investigated. Such a solution allows skipping the intermediate DC/DC boost converter and thus reducing conversion losses and complexity of a system. The inverter has to oaperate with low duty cycles, which, in turn, demands increasing of switching speed and thus requires application of advanced transistors. To evaluate the switching performance, studies were carried out with various types of switches, namely Si IGBT, Si MOSFET, Cascode SiC JFET, SiC MOSFET using classic gate drivers and proposed current source drivers. Detailed switching waveforms were obtained using the double pulse method and analyzed for each type of the switch. The switching speed was assessed and losses were evaluated. Two types of transistors were selected for testing in the VSI paired with an EMRAX 228 generator. Inverter efficiency data was obtained and analyzed for two types of transistors/drivers and the speed-torque curve applicable for a 3 kW turbine. It is shown that the suggested solution improves the efficiency of SSWTs’ inverters.

An Inverse Method for Wind Turbine Blade Design with Given Distributions of Load Coefficients

It is shown in the literature that wind turbine designs with different load distributions have different wake features. To systematically study how different load distributions affect turbine wakes, a method for designing variants of blades with different radial load distributions, but with approximately the same power (CP) or thrust coefficient (CT), is needed. In this work, an inverse design method based on the blade element momentum method and the multi-dimensional Newton’s method, with the normal and tangential force coefficients as the design objective and iterations for satisfying the CP or CT constraint, is developed. The proposed method is validated using the two-bladed small-scale NREL phase VI S809 wind turbine blade design and the three-bladed utility-scale NREL 5 MW wind turbine blade design. Four variants of the NREL 5 MW wind turbine, i.e., the Root-CP, Tip-CP, Root-CT, and Tip-CT designs, which represent the variants of the original design (NREL-Ori) with a higher load near the blade root and tip regions with approximately the same power coefficient (CP) or thrust coefficient (CT) as that of the NREL-Ori design, respectively, are then designed using the proposed method. At last, the flapwise blade bending moment and the power coefficients from different variants of the NREL 5 MW turbine are compared for different tip speed ratios, showing that the “Root” designs are featured by a wider chord near the root, lower blade bending moment, and higher power coefficients for tip-speed ratios greater than nine.

Performance analysis of shrouded invelox wind collector in the built environment

Shrouded wind turbines are emerging as a promising approach for integrating wind energy into residential areas. A wind turbine’s shrouding plays a key role in strengthening the wind speed in low-wind areas, thereby maximizing power generation. The wind speed is improved by various novel geometries, airfoils, and positioning of the turbines at various locations. In this research, further improvement in wind speed is attained by optimizing the shrouded profile using the Taguchi approach. A modified INVELOX is attached at the exit of the shroud for harnessing wind power at multi-stages using the shrouded turbine. A high turbulence environment at two distinct locations was chosen based on the standards of the International Wind Agency to validate the performance of the shrouded INVELOX small-scale wind turbines. The wind turbulence characteristics based on the urban atmospheric boundary layer inflow situation over the above locations are analyzed using computational fluid dynamics and validated with experimental results. The shrouded INVELOX increases the wind speed by 1.52 times the actual wind speed when located at low-rise buildings and increases by 1.68 times when located at the top of the tallest building. The shrouded INVELOX performs better in comparison with the shroud and INVELOX when operated separately.

Univariate analysis of scaling effects on the aerodynamics of vertical axis wind turbines based on high-resolution numerical simulations: The Reynolds number effects

The scale effect on aerodynamics determines, to some extent, the development trend and limitation of large vertical axis wind turbines (VAWTs). Among many factors, Reynolds number is an important one affected by such effects and is therefore often used as a criterion to distinguish between small-scale and large-scale wind turbines. In this paper, a dimensionless analysis was first conducted, and the results showed that scaling the wind turbine as a whole only led to a change in Reynolds number, while other key factors remained constant. Based on such understanding, a univariate analysis was then carried out to investigate the effect of Reynolds number variation due to scaling effects on the aerodynamic performance of VAWTs. In the study, a series of high-resolution numerical simulations were performed on a simplified single-bladed VAWT model. By directly scaling the model size, the operating Reynolds number of the wind turbine was made to vary in the range of 1×104 to 5×106 at a specific solidity and reduced frequency. The analysis shows that over the range of Reynolds number investigated, as the size of the wind turbine model increases, the flow separation nearby the blade decreases, the strength of the dynamic stall vortex becomes weaker, and the power coefficient of wind energy extraction generally tends to increase, thus indicating that large-scale wind turbine is generally beneficial aerodynamically. Specifically, when VAWTs operate in a Reynolds number ranging from 5×104 to 5×105, the power coefficient increases significantly as the size of wind turbine increases, while when operating in the range of 5×105∼5×106, the power coefficient still tends to increase, but in a decreasing increment ratio.

Recent developments and issues of small-scale wind turbines in urban residential buildings- A review

To address the future growth in energy demands, complete renewable power generation from environmental assets demands unique methodologies from every investigator. Wind energy harvesting in residential areas is one such approach. But the urban landscape and the physical challenges restrict the erection of small-scale wind turbines. Further, a significant degree of uncertainty leads to a lack of awareness of how dispersion in urban environments impacts turbine performance. This research looks into the potential productivity of wind turbine installations in urban areas, considering turbulence. These unique ambient conditions prevailing in a dynamic environment compared to flat terrains have made the harnessing of wind energy very difficult. Many researchers are still trying to find an effective methodology in these constrained circumstances. Since the characteristics of small-scale wind turbine models are undetermined, large-scale turbines fared well compared to small-scale wind turbine models. The feasibility and success of small and medium turbines in community homes were investigated in this study. The origins of the very uncertain nature of atmospheric boundary layer limitations are discussed in this work and subsequent successful developments by different researchers.

Particle Image Velocimetry Investigation of the Flow for the Curved Type Wind Turbine Shroud

Determining the flow structure in the flanged diffuser shrouding designed to be used for a wind turbine, plays a vital role in improving efficiency in small-scale wind turbine technology. In this study, the flow structure in the curved type flanged diffuser was investigated in terms of water flow velocity increase, by using particle image velocimetry (PIV) measurements. The dimensionless magnitude of the resultant velocity determined at downstream and up radial regions as well as at the flange downstream of the curved type wind turbine shroud, revealed that resultant velocity was increased by a factor of 1.5. This increase of the wind velocity will result the wind energy interacting with the rotor blades to be enhanced by 3.38 times more. By the designed shrouding component to be used in micro wind turbines, it is also aimed to start the power generations in these types at a lower value of cut-in wind speed value.

The impact of trailing edge flap on the aerodynamic performance of small-scale horizontal axis wind turbine

Despite the significant progress in the wind energy field, there is always space for new blade profiles to improve the efficiency and the energy extracted of HAWTs. To improve the performance of small-scale HAWTs, a new blade profile design using a fixed trailing-edge flap was investigated using blade element momentum (BEM) approach and validated using computational fluid dynamics (CFD) approach. The aim of this study is to obtain a new blade profile which has higher lift-to-drag coefficient for wind turbine by integrating a trailing-edge flap into a reference blade design. To determine the optimal blade profile, the annual yield based on the Weibull distribution is used. The full three-dimensional CFD analyses were performed on the new blade profile only. The BEM results show that at the design tip speed ratio of 7, the power coefficient of the new blade profile is 8.3% higher than the reference design. According to the new blade profile, the CFD method over-predicts the power coefficient compared with the BEM method. According to wind speed distribution in Turkey, the annual yield of the wind turbine with the reference blade profile and the new blade profile was found as 6378 kWh/year and 6944 kWh/year, respectively.

Wind Tunnel Probe Into an Array of Small-Scale Horizontal-Axis Wind Turbines Operating at Low Tip Speed Ratio Conditions

AbstractIn recent times, the small wind farms consisting of small-scale horizontal-axis wind turbines (SHAWTs) have emerged as suitable candidates for electric power generation. In view of this, an experimental study on the arrays of two SHAWTs has been performed in a wind tunnel to find the individual/combined performance(s) along with the downstream wake assessment. The rotor blades composed of Eppler E216 airfoil and having radius of 120 mm are designed using the blade element momentum theory. The operational limit of tip speed ratio (λ) is kept between 0.5 and 6. The upstream turbine (UsT) is capable to produce a maximum power coefficient (Cpmax) of 0.30 at a wind speed U = 8 m/s, whereas at the same wind speed, the downstream turbine (DsT) produces Cpmax values of 0.12, 0.13, and 0.15 when installed at a distance of 6R, 8R, and 10R from the UsT, respectively. Another notable feature is the change in the operational limit of λ for DsT due to the wake of UsT. The streamwise velocity measurement at the different downstream locations of UsT shows the formation of W-shape velocity deficit within the near wake regime that loses its shape as the distance downstream goes beyond 12R due to ∼60–70% flow recovery.

Performance assessment of straight and linearly tapered rotors through wind tunnel investigation for off-grid applications

The development of commercial wind turbine (WT) blade often accompanies many challenges due to its complex design process, geometric configuration and associated cost. In this backdrop, the article tries to put forward the applicability of a much simpler form of WT blades, which could be used in place of blade element momentum theory (BEMT) based turbine blades. In the present investigation, four small-scale horizontal-axis wind turbines model rotors having NACA0012 as its sectional profile has been designed and tested. The three model rotors opted to have straight and linearly tapered (SLT) blades, have been chosen in reliance on their simplicity and ease of fabrication. They are differentiated based on the root chord to tip chord ratio as M1 (1:1), M2 (5:3) and M3 (5:2), and subsequently compared with a BEMT rotor of a similar operational configuration. The wind tunnel investigation shows that the power coefficient for M1 is higher than M2 and M3. The favourable models M1 and M2 are capable of capturing power coefficient of, 37% and 24%. respectively, of the Betz-Joukowsky limit while operating at blade pitch angle less than 30°. Based on their operational characteristics, it is suggested to operate the modelled SLT rotors in the potential generation phase of the power characteristics curve to avoid a sudden drop in the rotor rotational speed.

Development of the Monitoring Program for an Integrated Small-Scale Wind and Solar Systems based on IoT Technology

For monitoring the energy supply from the hybrid small-scale wind turbine generator (WTG) and rooftop solar Photovoltage (PV) systems, this paper presents the design of a management program of the studied system based on the Internet of Things (IoT) technology. The proposed studied system consists of digital power meters that communicate wirelessly to the Programmable Logic Controller (PLC) through the ZigBee communication standard. By using a free cloud platform will greatly facilitate the Supervisory Control and Data Acquisition (SCADA) interface design work for a Human Machine Interface (HMI) or mobile phone. This system configuration may be easy to be fitted for collecting electrical information such as voltage, current, power, frequency of the system to be monitored. This is one of the cheap solutions deployed in small-scale hybrid power systems (HPS) or factories because wireless communication is very convenient in construction and installation.

Parametric Analysis Using CFD to Study the Impact of Geometric and Numerical Modeling on the Performance of a Small Scale Horizontal Axis Wind Turbine

The reliance on Computational Fluid Dynamics (CFD) simulations has drastically increased over time to evaluate the aerodynamic performance of small-scale wind turbines. With the rapid variability in customer demand, industrial requirements, economic constraints, and time limitations associated with the design and development of small-scale wind turbines, the trade-off between computational resources and the simulation’s numerical accuracy may vary significantly. In the context of wind turbine design and analysis, high fidelity simulation under full geometric and numerical complexity is more accurate but pose significant demands from a computational standpoint. There is a need to understand and quantify performance deterioration of high fidelity simulations under reduced geometric or numerical approximation on a single small scale turbine model. In the present work, the flow past a small-scale Horizontal Axis Wind Turbine (HAWT) was simulated under various geometric and numerical configurations. The geometric complexity was varied based on stationary and rotating turbine conditions. In the stationary case, simple 2D airfoil, 2.5D blade, 3D blade sections are evaluated, while rotational effects are introduced for the configuration 3D blade, rotor only, and the full-scale wind turbine with and without the inclusion of a nacelle and tower. In terms of numerical complexity, the Single Reference Frame (SRF), Multiple Reference Frames (MRF), and the Sliding Meshing Interface (SMI) is analyzed over Tip Speed Ratios (TSR) of 3, 6, 10. The quantification of aerodynamic coefficients of the blade (Cl, Cd) and turbine (Cp, Ct) was conducted along with the discussion on wake patterns in comparison with experimental data.