Performance Of Small Wind Turbine Research Articles

Multi-objective optimization of glass/carbon hybrid composites for small wind turbine blades using extreme mixture design response surface methodology

Small wind turbines (SWTs) are a prominent renewable energy technology for decentralized power generation. Blade material and its profile are vital parameters for the aerodynamic performance of SWTs. Traditionally E-glass fiber-reinforced composites (FRCs) are the widely accepted material for developing SWT blades. However, its application is limited by moderate tensile and fatigue properties. Alternatively, other FRC materials such as carbon, basalt and natural fiber composites are proposed as future materials for SWT blades. However, individual materials are observed to satisfy the requirements partially. Therefore, the hybridization of these materials, particularly Glass/Carbon composites is foreseen as a prospective solution for developing cost-competitive and high-strength SWT blades. There are various studies performed to obtain optimized glass/carbon hybrid composites. However, overall material properties required for SWT blades such as low cost, lightweight, moderate flexural strength and higher tensile and fatigue strengths have not been considered simultaneously during the optimization process. This work presents multi-objective optimization of Glass/Carbon hybrid composites using extreme mixture design response surface methodology (RSM) for SWT applications. The weight percentages of glass and carbon fibers are optimized to achieve desired material properties for SWT blades. The experiments are planned using extreme mixture design RSM and the regression models for desired material properties are developed with a 95% confidence level. RSM-based desirability function is employed to perform multi-objective optimization. Maximum composite desirability of 93.5% is achieved with optimal proportions of 37.9% and 27.1% for glass and carbon fibers respectively. An adequate tensile, flexural and fatigue strengths of 486.02, 435.41 and 316.27 MPa respectively are obtained for optimized glass/carbon hybrid composite at an optimum cost of 2228.76 Rs Kg−1 and density of 3.39 g cm−3. The regression models and optimization results are validated through a confirmation experiment with an error of less than 6.1%.

Steady and unsteady characteristics of circular arc airfoils for water pumping windmills

Accurate airfoil lift and drag data at low Reynolds number, Re, and high angles of attack, α, are needed to analyze the performance of small wind turbines, particularly their starting. In the current study, the steady and unsteady aerodynamic characteristics of circular arc airfoils (CAAs) with and without spars, as used in water-pumping windmills, were examined in a wind tunnel of 1 m2 cross section at Re<106. The tunnel was configured as an open jet and a closed section. The effects of varying geometrical characteristics on the CAA performance were investigated using a combination of thickness, camber, aspect ratio, and airfoil chord-to-tunnel height ratio. Using force transducers, the aerodynamic forces acting on the airfoils were measured directly for both increasing and decreasing α. The decreasing α measurements produce a higher lift–drag ratio than the increasing measurements, mostly in the post-stall region. In addition, “second stall,” was observed at large α in both the open and closed tunnels depending on the Re and tunnel blockage, but was much more prominent in the closed tunnel due to its wall constraining the wake and preventing the flow from switching from one regime to another. It was shown that the performance of all tested airfoils was sensitive to low Re under steady and unsteady conditions. The latter measurements for an airfoil oscillated at reduced frequencies, k≤0.06, are the first for CAAs. Results from this investigation provide a comprehensive airfoil dataset for the accurate blade element theory modeling of CAAs aerodynamic and starting performances.

A method to assess the performance of small wind turbines

While large wind farms are well monitored, with a wealth of data provided through a SCADA system, the only information about the behaviour of small wind turbines is often only through the metered electricity production. Given the variable electricity output, it is difficult to ascertain whether a particular electricity production in a metering period is the result of the turbine operating normally, or if a fault is resulting in a production less than possible. This paper presents a method to correlate metered electricity output from a set of 5 kW wind turbines with weather information from a weather station some distance from the turbine. That correlation will then be classified into ‘expected’ and ‘unusual’ performance using Principal Component Analysis.

Evaluation of the Influences of Different Roof Shapes on the Flow Properties and Performance of Small Wind Turbines

Small wind turbines offer a complement to photovoltaic systems and are becoming an interesting solution in the wake of rising energy prices. The measurement results indicate that some locations on and around the building are not suited for installing wind turbines, while others show increased wind potential. Due to limited space, rooftop mounting is an interesting alternative to free mounting on a mast from a technical point of view. For this reason, the influence of roof shapes on the flow on and behind the building was measured and the performance of two different types of small wind turbines was investigated. The turbines assessed in the project are VertikonM with a vertical axis and helix-shaped rotor blades, and Superwind 1250 wind turbine with a horizontal axis and centrifugal force pitch control. The results showed that there is an average increase in wind speed of 0.2 m/s on gable roofs at hub height (7 m). In comparison, there is an increase of 0.4 m/s on flat roofs at hub height (7 m). In relation to the performance of the turbines, high turbulence on the roof seems to cancel out this effect. The performance of the horizontal axis small wind turbine has not increased in comparison with gable roof and free-standing mast. For the vertical-axis turbine, a power increase by a factor of 2.23 was achieved between free-standing mast and gable roof. Vertical wind flow above the gable roof was identified as the main cause for power increase. The experiment was conducted on the Lichtenegg energy research park (Lower Austria) and its results make it possible to better identify all effects that affect the turbine output power.

Investigation of Wind Data Resolution for Small Wind Turbine Performance Study


 Small wind turbine sites, in general, use a 0.5Hz sampling interval and a 10-minute averaging interval for a feasibility study or turbine testing. Studies have established that the calculated performance variation of small wind turbines when averaging at large time intervals. The performance variation is larger for sites with high wind variability. However, these studies are often based on low sampling frequency and high averaging intervals. 
 
 
 In the present study, wind speed data has been measured at a high sampling frequency of 20Hz with an ultrasonic sensor. A dynamic model of a 50W Rutland wind turbine is used to analyse the simulated performance using wind speed data at a range of sampling intervals and some averaging intervals. The wind turbine and the anemometer are installed in a residential area of high wind variability. 
 
 
 The energy is calculated and compared directly using the wind turbine model and using the IEC recommended method of bins. The direct method results show that the rise in instantaneous sampling intervals up to 20 seconds has an insignificant effect on the energy output. Whereas, for 2-seconds sampled wind data averaged over 10-minutes, energy overestimates of 19% is observed. However, where only 10-minute interval averaged wind data are available, there is a significant underestimate in energy by 45%. The energy calculated using the method of bins overestimates the energy by 19% for high resolution wind data and underestimates by 22% for 10-minute average data.

Electrical design of a smart control and monitoring system for small horizontal-axis wind turbines

The popularity of small wind turbines would rise in future, because of electricity prices are still growing. Next generation of small wind-turbines can have higher efficiency values. Under wind gusts and turbulences, the system should be very sensitive to wind conditions. In this work, it is presented a control system that can improve the performance of commercial small-scale wind turbines by including active pitch and load control. We show the electrical design of a smart active pitch control to increase the energy generation of micro-wind turbines (< 5 kWp). The electrical design controls a simple mechanism that allows the rotation of the blades by using an actuator that moves the blades according to the energy desired. The load control is also shown. These two control strategies maximise the power output at all wind conditions, and can increase the performance of small wind turbines. Moreover, important signals that allow safety actions and feedback data are monitored. The electro-mechanical design is robust and economical compare to the traditional hydraulic solution, which will increase its potential adoptability by users.

Effect of the Blade Pitch on the Performance of Small Wind Turbine Exposed to Wind Stream of Various Angles of Attack

In wind turbines, several parameters can affect the productivity of the turbine, such as wind velocity, rotor area, blade aerodynamic design, and blade pitch. In this paper, the effect of various pitch angles for a small wind turbine was investigated. A system of two metal stands with same height is installed (i.e. on the same axis of streaming), the first stand holds an air blower which imitates the wind with constant air blowing. The other, holds a small wind turbine consists of a DC motor and metal hub (steel bush) with 3-blades with equal radial distance (120°). The pitch angle was adjusted at a certain degree of inclination (10°) in which the turbine stars to rotate, then readings of power and rotational speed were collected. The process then repeated with another 3 different angles (15°, 20°, and 25°). At the end, a fixed pitch angle degree was adjusted, and then the lowest and highest air velocity that affecting the blades rotation were measured.

Influence of Reynolds number on the performance of small horizontal axis wind turbine with fixed speed operation

ABSTRACT The Blade Element Momentum (BEM) theory is most commonly utilized to quickly assess the performance of horizontal axis wind turbine. However, the BEM theory requires the aerodynamic characteristic of the airfoil to evaluate the performance. Generally, the aerodynamic characteristics of airfoil in BEM theory for performance prediction of wind turbine with fixed rotor speed operation is obtained at an approximated fixed Reynolds number which may not accurately correspond to the operating Reynolds number over the blade. In the present work, the performance of a small wind turbine, with fixed rotor speed operation, and considering a range of approximated fixed Reynolds number (i.e., 0.5, 0.75, 1.00, and 1.25 million) and the operational Reynolds number over the blade for the aerodynamic characteristic of the airfoil has been evaluated and compared for a range of wind speeds i.e., 6, 8, 10, and 12 m/s. To incorporate the operational Reynolds number in the study, the aerodynamic characteristics of the airfoil have been mathematically represented as function of Reynolds number and angle of attack using an artificial neural network (ANN)-based model. The results suggest that inadequate Reynolds number consideration can led to high discrepancies up to 18.6% in power coefficient prediction.

Effect of averaging time windows on wind resource assessment of small wind turbines

AbstractIn wind energy, the general practice in assessing the wind resource of a site is to employ a 10‐min averaging to measured wind data. However, small wind turbines (SWTs) with rotor diameters <15 m will have a shorter response time scale; thus, an averaging time window of 10 min is too long for accurate wind resource assessments. The current study investigates the effect of averaging time windows on wind resource assessment and power estimation of SWTs. To that end, wind data from a 1‐year measurement campaign is analysed using two short‐term averaging windows of 30 and 60 s and two long‐term averaging windows of 5 and 10 min. Although the average wind speed over the 1‐year period is 1.3 m/s with all four windows, when wind speeds higher than 3 m/s are considered, the average wind speed obtained using a 30‐s averaging window is 8% higher than that obtained using a 10‐min window. Power prediction using the 10 kW SWT shows that the predicted power using a 30‐s window is almost twice as large compared to that estimated using a 10‐min window. Finally, the rotational speed of the SWT obtained with short‐term averaging shows better agreement with that computed by direct modelling of the turbine with the measured wind speed as the input to the model. The study thus shows that the performance of SWTs will be better predicted if short‐term averaging windows are used.

A Comprehensive Comparative Investigation of the Lifting Line Theory and Blade Element Momentum Theory Applied to Small Wind Turbines

Abstract Small wind turbines (WTs) are adequate for electricity generation in isolated areas to promote local expansion of commercial activities and social inclusion. Blade element momentum (BEM) method is usually used for performance prediction, but it generally produces overestimated predictions since the wake effects are not precisely accounted for. Lifting line theory (LLT) can represent the blade and wake effects more precisely. In the present investigation, the two methods are analyzed and their predictions of the aerodynamic performance of small WTs are compared. Conducted simulations showed a computational time of about 149.32 s for the Gottingen GO 398 based rotor simulated by the BEM and 1007.7 s for simulation by the LLT. The analysis of the power coefficient showed a maximum difference between the predictions of the two methods of about 4.4% in the case of Gottingen GO 398 airfoil-based rotor and 6.3% for simulations of the Joukowski J 0021 airfoil. In the case of the annual energy production, a difference of 2.35% is found between the predictions of the two methods. The effects of the blade geometrical variants such as twist angle and chord distributions increase the numerical deviations between the two methods due to the big number of iterations in the case of LLT. The cases analyzed showed deviations between 3.4% and 4.1%. As a whole, the results showed good performance of both methods; however, the LLT provides more precise results and more information on the local flow over the rotor blades.

Effects of leading edge slat on the aerodynamic performance of low Reynolds number horizontal axis wind turbine

The present study considers the use of a slat near the leading edge of an airfoil to delay or completely cancel separation and thus improves the performance of small wind turbines, in addition to lowering the cost of the blade by reducing the used material. Flow around the S809 airfoil with a slat is numerically simulated using ANSYS 2019 R1 (CFD) program. The present work concentrates on two geometrical parameters namely the location of the slat relative to the base airfoil and the chord size of the slat. Relative to the total chord length of the main airfoil, a slat with a chord length 10% is located at range of distances +3.6% to +10.8% in y direction, slat located at 9% shows the best lift coefficient. To study the effect of slat size, slat sizes range from 5% to 12.5% are numerically investigated, slat size 7.5% shows the best lift coefficient and attached flow over the airfoil for a wide range of angles of attack. The improvement is achieved with the same total chord length with 12% saving of material which corresponds to 6% of the total cost of the turbine.

Effects of Rotor-Blade Deformation onto Performance of Domestic Wind Turbines

Paper is focused on the influence that blade deformations by torsion and bending due to drag, lift, and gravitational effects has on the performance of small wind turbines. A blade model of stiff finite elements connected by rotating junctions is used. Mechanical deformations are simulated by controlled gravity and torsional forces, and their effects are measured through the response of the wind turbine. Tests have been run before and after the deformation process under different wind conditions in a wind tunnel. No centrifugal stiffening and gyroscopic moments are considered due to the low angular speed. Wind speed was controlled to determine the effect of the deformation on the performance of the wind turbine as a function of the wind power. The results have shown that in all cases, the effects of the deformation are negative, and the decrease in power has been calculated depending on wind conditions.

Power loss by blade deflection in flexible rotor wind turbines

Effects of deflection onto the performance of small wind turbines with flexible rotor-blades have been studied and analysed. The goal of the study has been the evaluation of the wind turbine output power loss due to angular deflection because of bending effects caused by gravity. Wind turbine blades have been deformed under constant load at the tip of the blade for periods up to 40 days. Deformation process has been accelerated using a very heavy load and the corresponding angular deflection has been obtained. Wind turbine performance has been characterized through the P-V curve for different wind speed operation conditions. Tests have been run for different deformation states to compare the evolution of the power loss with angular deflection. Results from experimental tests have shown there is a constant power loss with deformation increase. Power reduction for angular deflection of 2.3o is between 35% and 45% for blade tip wind speed from 27.6 m/s to 42 m/s. Power coefficient, C p , has also been analyzed and determined for the angular deflection of 2.3o and 4.3o; the reduction of the power coefficient value has been computed through a power loss factor, f P , that shows a reduction in the range of 25% to 50% for the 2.3o angular deflection, and between 45% and 55% for the angular deflection of 4.3o.

Numerical study of the effect of surface grooves on the aerodynamic performance of a NACA 4415 airfoil for small wind turbines

Indented surface grooves can eliminate the laminar separation bubbles formed on airfoil surfaces, and thus have the potential to improve the aerodynamic performance of small wind turbines. In this study, a three-equation transitional turbulence model was selected and validated with experimental data to simulate the 2D flow around a NACA 4415 airfoil. Parametric simulation of surface groove characteristics was then conducted to investigate their effects on aerodynamic behavior. It was found that the recess depth ratio (h/δ, h: groove recess depth, δ: baseline boundary layer thickness) is the key influencing factor among the groove feature parameters, with the most effective value between h/δ=1.0 and 1.5. A smaller aspect ratio of recess depth to groove width is required to trap the vortex for a shallow recess depth, while a higher aspect ratio can stabilize the vortex for a deep recess. The endpoint of a groove can affect the potential vortex size within it, and the optimum endpoint is located around 0.16c (c: airfoil chord). Moreover, a rectangular groove especially for a recess depth ratio h/δ=1.2−1.5 offers better aerodynamic performance than an arc groove, as the rectangular configuration more efficiently restricts the flow motion inside the groove.

Comparative Study of New Airfoils for Small Horizontal Axis Wind Turbines

Abstract The high cost and poor performance of small wind turbines make them not widely used. In an attempt to meliorate this situation, the authors propose to investigate alternative airfoils with different chord and pitch angle distributions that permit low manufacturing, installation and maintenance costs, as well as high efficiency. To achieve these goals, two airfoil sections, Gottingen and Joukowski, together with different chord and pitch angle distributions were simulated by using a validated numerical code based on the blade element momentum (BEM) method. The chord geometry includes constant, linear, and elliptic distributions while the twist angle includes constant and linear distributions. The results reveal that the linear pitch distribution reduces the thrust in the intermediate region of the blade and the bending moment at the root and reduces the power coefficient for both rotors. Rotors with elliptic chord distribution show increased forces in the intermediate region. Joukowski based blades with elliptic chord distribution show lower thrust compared with those with linear chord distribution. The linear chord distribution increases the thrust in the intermediate region and reduces it at the tip and root regions. Blades with multiple airfoils show marginal improvement. The Gottingen and Joukowski based rotors have similar annual energy production (AEP). The Joukowski based rotor with linear pitch and linear chord distribution shows better performance at low velocities and easy to manufacture which makes it a good candidate for small power wind turbines.

Aerodynamic performance prediction of SG6043 airfoil for a horizontal-axis small wind turbine

In order to design a small wind turbine, the performance of SG604x airfoil and previously existing 15 airfoils was reviewed at a Reynolds number of 300,000, which suggests the maximum lift-to-drag ratio of the airfoils, corresponding lift coefficient, and the maximum lift coefficient for both free and fixed transition. The SG6043 airfoil provides enhanced lift-to-drag ratio performance as compared with previously existing airfoils at a Reynolds number of 300,000. Only a SG6043 airfoil for small wind turbine performance prediction is applied along the length of the blades. This is why a blade constructed using airfoils of different performance may not exhibit the expected performance. A code based on BEMT(Blade Element/Momentum Theory) was used for performance predictions of small horizontal axis wind turbine. As important input parameter of BEMT, distributions of chord and twist was derived by the optimization method using genetic algorithm. The power performance prediction of airfoil data of SG6043 using BEMT is presented over a wide range of wind speeds. The results of BEMT using SG6043 show that the rated wind speed can be reduced to 10 m/s for a rotor radius of 7.25m and a rating of 32kW. The reduced rated wind speed would increases the annual capacity factor as compared the existing airfoils.

Investigation of Small Wind Turbine Performance in Natural Wind with Low Turbulent Intensity

Investigation of Small Wind Turbine Performance in Natural Wind with Low Turbulent Intensity

Numerical investigation of the optimum wind turbine sitting for domestic flat roofs

The power capacity of roof mounted wind turbines is dependent on several factors which influence its energy yield. In this paper, an investigation has been carried out using Computational Fluid Dynamics (CFD) to determine flow distribution and establish an optimum mounting location for a small wind turbine on a domestic flat roof. The realisable k-ε and SST k-ω turbulence models were compared to establish their consistency with one another with respect to the physical domain. Nine mounting locations were considered for a pole mounted wind turbine. Three windward positions on the upwind side of the flat surfaced building were considered as viable locations for mounting the small wind turbine. Out of the three windward locations, the central upwind (1,0) mounting position was seen to be producing the highest velocity of 5.3 m/s from the available ambient velocity which was 4 m/s. Therefore, this mounting location provided the highest extractable power for the wind turbine. Conclusively, wind properties along with the mounting locations can play a significant role in either enhancing or diminishing the small wind turbine's performance on a domestic flat roof.

Study on small wind turbine icing and its performance

Wind turbines often suffer from severe ice during winter. Ice on the blades changes the airfoil profile, thereby causing wind turbine power loss. The icing characteristics and output of small horizontal-axis wind turbine were experimentally studied in an artificial climate chamber, and a 3D ice accretion wind turbine model was proposed to simulate glaze ice. Results show that ice rapidly reduces the rotation speed and load power of the wind turbine. The ice growth rate rises initially and then declines with time. Ice linearly increases from the root to the tip and mainly accumulates at the leading edge. As the rotation speed slows down, the ice-covered area moves to the pressure side. Higher wind velocity and lower temperature lead to more severe ice, but they do not change the ice shape. The shaft torque of the iced turbine shows a rising trend, and then it falls, thereby decreasing the shaft power and power coefficient. Ice load seems to have a greater effect than the deterioration of aerodynamic characteristics on the rotor performance of small wind turbines.

Computational studies on small wind turbine performance characteristics

To optimize the selection of suitable airfoils for small wind turbine applications, computational investigation on aerodynamic characteristics of low Re airfoils MID321a, MID321d, SG6040, SG6041, SG6042 and SG6043 are carried out for the Reynolds number range of (0.5- 2)×105. The BEM method is used to determine the power coefficient of the rotor from the airfoil characteristics; in addition, the blade parameters like chord and twist are also determined. The newly designed MID321a airfoil shows better aerodynamic performance and maximum power coefficient as compared with other investigated airfoils for wider operating ranges.