Small-scale Wind Turbine Research Articles

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.

Aerodynamic Design and Wind Tunnel Tests of Small-scale Horizontal-axis Wind Turbines for Low Tip Speed Ratio Applications

Abstract In recent times, the application of small-scale horizontal axis wind turbines (SHAWTs) has drawn interest in certain areas where the energy demand is minimal. These turbines, operating mostly at low Reynolds number (Re) and low tip speed ratio (λ) applications, can be used as stand-alone systems. The present study aims at the design, development, and testing of a series of SHAWT models. On the basis of aerodynamic characteristics, four SHAWT models viz., M1, M2, M3, and M4 composed of E216, SG6043, NACA63415, and NACA0012 airfoils, respectively have been developed. Initially, the rotors are designed through blade element momentum theory (BEMT), and their power coefficient have been evaluated. Thence, the developed rotors are tested in a low-speed wind tunnel to find their rotational frequency, power and power coefficient at design and off-design conditions. From BEMT analysis, M1 shows a maximum power coefficient (Cpmax) of 0.37 at λ = 2.5. The subsequent wind tunnel tests on M1, M2, M3, and M4 at 9 m/s show the Cpmax values to be 0.34, 0.30, 0.28, and 0.156, respectively. Thus, from the experiments, the M1 rotor is found to be favourable than the other three rotors, and its Cpmax value is found to be about 92% of BEMT prediction. Further, the effect of pitch angle (θp) on Cp of the model rotors is also examined, where M1 is found to produce a satisfactory performance within ±5° from the design pitch angle (θp, design).

Software in-the-Loop Simulation of an Advanced SVM Technique for 2ϕ-Inverter Control Fed a TPIM as Wind Turbine Emulator

An appropriate modulation scheme selection ensures inverter performance. Thus, space vector modulation (SVM) is more efficient and has its own distinct advantages compared to other pulse width modulation (PWM) techniques. This work deals with the development of an advanced space vector pulse width modulation (SVM) technique for two-phase inverter control using an XSG library to ensure rapid prototyping of the controller FPGA implementation. The proposed architecture is applied digitally and in real time to drive a two-phase induction motor (TPIM) for small-scale wind turbine emulation (WTE) profiles in laboratories with minimum current ripple and torque oscillation. Four space voltage vectors generated for the used SVM technique do not contain a zero vector. Hence, for an adequate adjustment of these four vectors, a reference voltage vector located in the square locus is determined. Considering the asymmetry between the main and auxiliary windings, the TPIM behavior, which is fed through the advanced SVM controlled-two-phase inverter (2ϕ-inverter), is studied, allowing us to control the speed and the torque under different conditions for wind turbine emulation. Several quantities, such as electromagnetic torque, rotor fluxes, stator currents and speed, are analyzed. To validate the obtained results using both Simulink and XSG interfaces, the static and dynamic characteristics of the WTE are satisfactorily reproduced. The collected speed and torque errors between the reference and actual waveforms show low rates, proving emulator controller effectiveness.

Investigating the Prospect of Small-Scale Wind Turbines Based on Regional Wind Velocities in Bangladesh

The wind turbine has the advantage of operating uninterruptedly, which ensures a constant source of electricity. This investigation includes a clear overview of the wind velocity, the flow direction; the amount of energy reserved, suitable regions for wind turbine installation, etc. The feasibility and possibility of installing a wind energy conversion system for several locations in Bangladesh are analyzed. A brief study of wind characteristics in different locations in Bangladesh is reported. Wind data obtained from the Bangladesh Meteorological Department (BMD) for Mongla, Patuakhali, Kutubdia, and Bhola stations are analyzed through wind rose, frequency distribution, and average wind velocity. The performance of suitable small-scale wind turbines will be assessed in order to confirm the prospect of wind turbines in Bangladesh.

A supervised machine-learning method for optimizing the automatic transmission system of wind turbines

Large-scale wind turbines mostly use Continuously Variable Transmission (CVT) as the transmission system, which is highly efficient. However, it comes with high complexity and cost too. In contrast, the small-scale wind turbines that are available in the market offer a one-speed gearing system only where no gear ratios are varied, resulting in low efficiency of harvesting energy and leading to gears failure. In this research, an unsupervised machine-learning algorithm is proposed to address the energy efficiency of the automatic transmission system in vertical axis wind turbines (VAWT), to increase its efficiency in harvesting energy. The aim is to find the best adjustment for VAWT while the automatic transmission system is taken into account. For this purpose, the system is simulated and tested under various gear ratios conditions while a centrifugal clutch is applied to automatic gear shifting. The outcomes indicated that the automatic transmission system could successfully adjust the spinning in line with the wind speed. As a result, the obtained level of harvested voltage and power by VAWT with the automatic transmission system are improved significantly. Consequently, it is concluded that automatic VAWTs, equipped with the machine-learning capability can readjust themselves with the wind speed more efficiently.

Impact of Turbulence and Blade Surface Degradation on the Annual Energy Production of Small-scale Wind Turbines

Impact of Turbulence and Blade Surface Degradation on the Annual Energy Production of Small-scale Wind Turbines

Investigation on the Performance of a Portable Power Generation System with a Low-Cost Vertical Axis Wind Turbine

The purpose of this project was to develop an innovative, small-scale, and portable vertical axis wind turbine for power generation. The wind turbine was simple in design and economical. Wind speeds ranging from 2.0ms-1 to 7.0ms-1 were tested on the proposed wind turbine. The experiments revealed that the turbine required a minimum wind speed of 3.9ms-1 to operate. According to the results, the proposed turbine achieved its maximum power output of 5.6W at a rotational speed of 65rpm when the wind speed was 7.0m/s. Additionally, voltage and current increased proportionately with increasing wind speed. The proposed system showed an average coefficient factor between 0.10 and 0.12. This portable wind turbine potentially revolutionizes industry while raising public awareness about clean and renewable energy.

Screening analysis and unconstrained optimization of a small-scale vertical axis wind turbine

The demand for alternative and renewable energy sources has been substantially growing in recent years, mainly steered by economic and environmental inconveniences of conventional energy sources, such as oil and its derivatives. In this context, wind energy has emerged as an attractive renewable source, envisioning possibilities of developing more efficient equipment to meet the ever-growing energy demand. In this work, we coupled Computational Fluid Dynamics (CFD) with an optimization based on response surface (RS) methodologies to find an optimal design for a small-scale NACA 0021 Darrieus vertical axis wind turbine (VAWT) operating at a tip speed ratio of 2.63. For that, we investigated four geometric parameters: number of blades (N), rotor diameter (D), chord length (c), and pitch angle (β). For the numerical model, we considered a two-dimensional, incompressible, turbulent, and unsteady flow regime. A sensitivity analysis (SA) via Morris’ method was performed to identify the influence of the four geometric parameters on the turbine aerodynamic performance. Our results reveal that the pitch angle (β) contributes the most (58%) to the turbine performance. The resulting optimized turbine design increased the conversion efficiency by 40%. Additionally, we also present a detailed discussion on the flow phenomenology considering the impact of each one of the four geometric parameters on the power coefficient. Finally, the strategy adopted here, in which a qualitative sensitivity analysis combined to the response surface and unconstrained optimization, was shown to be robust and can be applied to high-dimensional and computational-expensive CFD models to reduce costs with adequate results regarding fluid flow phenomena.

Impact of compact diffuser shroud on wind turbine aerodynamic performance: CFD and experimental investigations

In the present work, the influence of a compact diffuser on aerodynamic behavior of small-scale wind turbine is analyzed using both CFD and experimental approaches. The present work aims to obtain a compact diffuser shroud while ensuring high aerodynamic performance in order to reduce the fabricating costs, materials, and structural loads on the mast. In this regard, a unique optimization approach is employed to optimize the geometrical features of the shroud profile including length of both entrance and diffuser sections, radii of both diffuser and entrance area. The shroud profile is mathematically described using second-order polynomial functions. The optimization findings affirmed that the total length of optimized shroud profile is shorter by approximately 6 % than the baseline (Cii) configuration. However, the wind speed obtained from the optimized shroud profile shows an improvement of 1.58% compared to the baseline configuration at the throat area. A high-fidelity CFD simulation of the wind turbine equipped with an optimized shroud profile using commercial software SATR-CCM+ was performed to evaluate the overall aerodynamic performance of the wind lens system. Both conventional and shrouded wind turbines were investigated for two different cases: constant rotor speed, and constant wind speed. Furthermore, an experimental test was implemented for both conventional and shrouded turbines under various environmental conditions using an open-loop wind tunnel. A systematic comparison between CFD results with the corresponding experimental data for both turbines is performed. It is evident that placing an optimized shroud around the rotor improves the aerodynamic performance more than twofold compared to the bare turbine. Moreover, results revealed that Cp obtained from shrouded Wind Turbine increased by approximately 66.4 % compared to the conventional one based on CFD results, whereas, it has increased by 69.3 % according to the experimental data.

A Novel 10 kW Vertical Axis Wind Tree Design: Economic Feasibility Assessment

A novel, small-scale vertical axis wind turbine tree was designed using turbines combining both Darrieus and Savonius blades. We tested for economic viability using wind data collected at a site in Surat Thani, Thailand. The Weibull distribution and Monte Carlo modeling with financial indices (Levelized Cost of Electricity (LCOE), Net Present Value (NPV), Internal Rate of Return (IRR), and Simple Payback Period (SPP)) were used to analyze data. We found that monthly mean wind speeds varied from 2.35 m/s in October to 2.84 m/s in February, corresponding to a wind power of 28.43 W/m2 and 42.68 W/m2. The average annual power output was 1446.1 kWh for May 2019 to April 2021. Results show that for turbine cut-in to cut-out speeds (2 m/s to 15 m/s), the prototype has potential economic feasibility (NPV > 0 for 64.93%), although the small capacity of the wind tree, in combination with the low average wind speed at the Surat Thani test site, showed a lack of economic viability at this specific location (NPV = USD − 20,946.29). A higher-wind-speed location (Chiang Mai) showed viability, especially at a 10 m height (NPV > 0 for 84.83%). We discuss potential conditions that would make broader use of the prototype feasible.

Wind Tunnel Tests of a Model Small-Scale Horizontal-Axis Wind Turbine Developed From Blade Element Momentum Theory

Abstract The small-scale horizontal-axis wind turbines (SHAWTs) have emerged as the promising alternative energy resource for the off-grid electrical power generation. These turbines primarily operate at low Reynolds number and low tip speed ratio conditions. Under such circumstances, the airfoil selection and blade design of a SHAWT becomes a challenging task. The present work puts forward the necessary steps starting from the aerofoil selection to the blade design and analysis by means of blade element momentum theory (BEMT) for the development of four model turbine rotors composed of E216, SG6043, NACA63415, and NACA0012 airfoils. This analysis shows the superior performance of the model rotor with E216 airfoil in comparison with other three models. However, in the subsequent wind tunnel study with the E216 model, a marginal drop in its performance due to mechanical losses has been observed.

Evaluation of wind energy potential for different regions in Lebanon based on NASA wind speed database

The grid-connected system can be an attractive solution to reduce electricity consumption, dependence on utility power, and increase electricity generation from renewable energy resources like wind energy for residential electricity users. Based on 33-year wind data (1983-2020), this study investigates the potential of wind energy at different locations ((Akkar, Baalbek, Beirut, Zahlé, Baabda, Nabatieh, Tripoli, and Sidon) in Lebanon using the Weibull distribution function. Monthly NASA wind speed data during the period (1983-2020) were used to estimate the wind energy potential. The result showed that the averaged wind speeds at the selected regions are varied from 3.695m/s to 4.457m/s at the height of 10m. Furthermore, the annual wind power density was estimated at various heights (10m, 30m, and 50m). The results demonstrated that small-scale wind turbines are recommended to be used for generating electricity from wind in the selected regions. Finally, the performance of WRE.060 / 6 kW (vertical axis wind turbine) and Proven WT 6000 (horizontal axis wind turbine) was done based on the monthly NASA wind speed database.

Economic Feasibility of a Small-Scale Wind Turbine in Coastal Area of South Sulawesi

To evaluate the exploitation potential of wind energy in the coastal area of South Sulawesi, Indonesia, an investigation on the economic feasibility of this project was performed. A 300-watt horizontal wind turbine was used as an example installed turbine. The wind speed range of 4-7 m/s which was the wind speed data in the coastal area of South Sulawesi was computed. The main economic analysis method employed was Capital Budgeting Analysis (CBA) method. In this method, 4 (four) indicators were used to evaluate the feasibility of the project which are payback period (PBP), net present value (NPV), internal rate of return (IRR), and benefit-cost ratio (BCR). A visual basic computer program based on the CBA method was also developed to make the computation more convenient. From the study, it was found that the wind speed range of 4-6 m/s resulted in a non-feasibility project while the highest wind speed (7 m/s) was found to be quite strong to make the project feasible.