CFD Analysis and Blade Optimization of a Small Horizontal Axis Wind Turbine

<abstract> <p>The paper deals with small wind turbines for grid-independent or small smart grid wind turbine systems. Not all small turbine manufacturers worldwide have access to the engineering capacity for designing an efficient turbine. The objective of this work is to provide an easy-to-handle integrated design and performance prediction method for wind turbines and to show exemplary applications.</p> <p>The underlying model for the design and performance prediction method is based on an advanced version of the well-established blade-element-momentum theory, encoded in MATLAB™. Results are (i) the full geometry of the aerodynamically profiled and twisted blades which are designed to yield maximum power output at a given wind speed and (ii) the non-dimensional performance characteristics of the turbine in terms of power, torque and thrust coefficient as a function of tip speed ratio. The non-dimensional performance characteristics are the basis for the dimensional characteristics and the synthesis of the rotor to the electric generator with its load.</p> <p>Two parametric studies illustrate typical outcomes of the design and performance prediction method: A variation of the design tip speed ratio and a variation of the number of blades. The predicted impact of those parameters on the non-dimensional performance characteristics agrees well with common knowledge and experience.</p> <p>Eventually, an interplay of various designed turbine rotors and the given drive train/battery charger is simulated. Criterions for selection of the rotor are the annual energy output, the rotor speed at design wind speed as well as high winds, and the axial thrust exerted on the rotor by the wind. The complete rotor/drive train//battery charger assembly is tested successfully in the University of Siegen wind tunnel.</p> </abstract>

Review of aerodynamic developments on small horizontal axis wind turbine blade

The wind power industry has experienced fast and tremendous growth, globally, in recent years. Consequently, there is a growing interest in investigating aerodynamics and aeroacoustics characteristics of wind turbines and developing environmental standards aimed at decreasing noise levels in the design and manufacture of these machines. This study was carried out in the Carleton University Wind Induced Dynamic Laboratory (WInDLab) that was designed to evaluate and quantify noise levels emitted by a small horizontal axis wind turbine. This investigation provided the first-ever set of measurements carried out in the WInDLab following the successful installation of the wind turbine. The background acoustic data obtained for the wind tunnel showed that the wind tunnel is not quiet enough for measurements of the type undertaken. The wind tunnel would need to be silenced and acoustically treated to capture noise with low frequencies. Recommendations for further work have been provided.

In recent years, the energy production by wind turbines has been increasing, because its production is environmentally friendly; therefore, the technology developed for the production of energy through wind turbines brings great challenges in the investigation. The use of wind energy worldwide has overgrown in recent years to reduce greenhouse gas emissions. Wind power is free, but the installation and maintenance of wind turbines still remain costly. Wind vitality is the second biggest wellspring of sustainable power source after hydropower. However, it has not yet accomplished full matrix equality with fossil vitality sources. In this work experimental design of small HAWT for home electricity has been designed and analysed in the laboratory at the Libyan Academy for Postgraduate Studies, Al-Bayda-Libya. Experimental work was used in this paper to evaluate the wind energy data in Al-Bayda, East of Libya. The field tests and measurements proved that the present turbine is efficient and has long life-time and needs minimum maintenance. Wind turbines convert wind energy into electricity. The efficiency of this conversion is measured by comparing the incoming winds speed and the output power. From the experimental work it was found that the present turbine is efficient, easy to construct and assembly, has long life-time and needs minimum maintenance, suitable for different sites such as urban, suburban, rural, and sea coast and the output power of the turbine covers the consumption of many electric devices.

Small wind turbines are gaining popularity due to their ability to meet community or domestic needs in isolated areas with relatively easier installation and lower cost than large wind turbines. This study looks at optimizing airfoils for use in small horizontal axis wind turbines. The optimization looks to maximize the lift coefficient (Cl) while minimizing or fixing the drag coefficient (Cd). To satisfy these two objectives a multi–objective genetic algorithm is used. The airfoil is parameterized using a composite Bezier curve with two Bezier segments and 11 control points. Appropriate curvature conditions are implemented at the leading and trailing edge of the airfoil and geometric constraints are applied to maintain the maximum thickness between 8% to 14% of the chord for structural reasons. An existing genetic algorithm (GA) code is modified in C++ to generate suitable airfoils using the 13 control points and pass the coordinates to a solver for analysis. As a result four new airfoils are generated for application in low Reynolds number (Re) flow. The characteristics and suitability of the four airfoils are discussed while comparing them to the popular SG6043 airfoil.

The formation and evolution of laminar separation bubbles on a horizontal axis wind turbine blade in the transitional flow regime are investigated using Large Eddy Simulations. Both rotating and translating cases of a blade element, based on a small horizontal axis wind turbine, are analyzed to distinguish the specific aerodynamic effects introduced by rotation. The results demonstrated that in the rotating case, the roll-up vortices developed through Kelvin–Helmholtz instability appear shorter, inclined at varying angles along the span, and break down at various locations along the span, in contrast to the continuous two-dimensional structures of the Kelvin–Helmholtz vortices observed in the translating case. Furthermore, in the rotating case, the Coriolis force induces a stabilization of the boundary layer by enhancing momentum transfer, promoting an earlier transition to turbulence and facilitating a rapid reattachment of the flow. Centrifugal force drives radially outward flow, displacing the bubble laterally, restricting its growth and limiting its extent along the blade surface. These effects result in a 66.4% thinner bubble, leading to a 26.7% reduction in lift, and a 36.3% reduction in drag compared to the translating case. These results demonstrate that, unlike large wind turbines, rotation in small horizontal axis wind turbines can degrade lift performance due to reduced effective curvature, despite improving aerodynamic efficiency due to the accompanied drag reduction. This study provides insights into laminar separation bubble behavior under rotation and contributes to a better understanding of the physics, aiding investigations and improvements in performance prediction models for the transitional flow regime.

This study employs a comprehensive combination of experimental and numerical methodologies to delve into the aeroacoustic attributes of a small horizontal axis wind turbine with optimized blades. The experimental investigation is conducted within a semi-anechoic chamber, where both original and optimized geometry models are meticulously positioned to measure the sound pressure levels across a range of rotational speeds and positions. In parallel, the numerical simulations employed the large eddy simulation, complemented by the Ffowcs Williams–Hawkings analogy, facilitating detailed examinations of both aerodynamic and acoustic aspects in the original and optimized modes. The findings reveal a subtle enhancement in aerodynamic performance with the optimized serrated blade configuration when compared to the original. Nevertheless, the reduction in noise levels within the frequency domain was remarkable, culminating in an impressive overall sound pressure reduction of about 10 dB. Furthermore, an intriguing observation emerged from noise measurement in acoustic room: the noise production experiences a marked escalation as the turbine rotational speed intensifies, particularly within the downstream domain. The lateral noise level is found to be lower compared to the axial direction and the reduced noise emission for the serrated optimized blade is more dispersed in the plane of rotation than the original blade, which was pointed out to be nearly uniform. The results provide valuable insights into the interplay of aerodynamics and aeroacoustics in the context of small wind turbines with optimized blades.

Accurate modeling of wind speed distributions is a crucial step in the design and sizing of small wind turbines. However, most current studies rely solely on the two-parameter Weibull distribution, without rigorous statistical analysis or comparison with other methods. This study presents a statistical analysis for the sizing of a small horizontal-axis wind turbine in northern Morocco. The proposed framework integrates hub-height optimization, probabilistic wind distribution modeling, and turbine parameter computation within a unified and robust methodology. The site hourly wind speed data, obtained from PVGIS, were extrapolated to an optimal hub height of 29 m using a power-law formulation combined with a cost-energy optimization approach. Then multiple distribution models were evaluated, which are the Weibull, Champernowne distribution, and kernel density estimation (KDE). Their performance was assessed using both conventional pointwise error metrics (RMSE and MAE) and distributional divergence measures, namely, Jensen‒Shannon divergence (JSD) and the Wasserstein distance (WD). Although the least-squares Weibull model produced the lowest pointwise errors (RMSE = 0.0136, MAE = 0.0103), it exhibited some distributional misspecification (JSD = 0.0132, WD = 0.0307) concentrated in the upper tail. Finally, based on a piecewise power-curve integration, the resulting turbine design parameters correspond to a swept area of 37.82 m², a blade length of 3.47 m, and a rated power of 8.28 kW to meet an annual energy demand of 33159 kWh. The results demonstrate that distributional metrics reveal modeling biases in the Weibull approach that remain undetected by traditional pointwise evaluation methods, with important implications for accurate energy yield prediction and turbine sizing reliability.

A Direct Approach of Design Optimization for Small Horizontal Axis Wind Turbine Blades

Dynamic and static frequency of the rotor about diameter of 1.4m small horizontal axis wind turbine was tested by using PULSE16.1 structural vibration analysis system., through combining the data of static frequency to identify rotor Dynamic frequency using spectrum analysis method. The conclusions found that, at a yaw condition of constant rotor speed, vibration acceleration of axial movement, disc effect and first order vibration of rotor increased with the increase of the yaw angle. The reason was that yaw exciting force which generated by the yaw behavior increased with the increase of yaw angle. At a constant load yaw, vibration acceleration of axial float, disc effect increased with the increase of the yaw angle. At the yaw condition of constant load R=82Ω、R=118Ω and the yaw angle 25°,30°,the acceleration value sharp increased and occurred the machine resonance phenomenon due to the tower instability. First order symmetric and anti symmetric vibration acceleration of rotor decreased with the increase of the yaw angle. The reason was that after the wind turbine yaw, the speed decreased of rotor caused the centrifugal force of the blades decreased, the impact of the centrifugal load changed was far greater than yaw exciting force for the first order vibration acceleration. The study also found that vibration acceleration values of rotor first order anti symmetric was ​​greater than axial movement, disc effect and first order symmetric vibration acceleration values, which shows that stress concentration in root of blade was large and the blade fatigue damage was more serious. This paper related research results can provided a new analytical thinking for rotor fatigue damage or breakage occurred frequently in wind turbine operation process, and may provide a reference for the vibration characteristics of rotor in the process of yaw.

Hydraulically actuated horizontal axis wind turbine pitch control by model free adaptive controller

A small wind turbine blade was designed and optimized in this research paper. The blade plays an important role, because it is the most important part of the energy absorption system. Consequently, the blade has to be designed carefully to enable to absorb energy with its greatest efficiency. The main objective of this paper is to optimized blade number and selection of tip speed ratio corresponding to the solidity. The power performance of small horizontal axis wind turbines was simulated in detail using blade element momentum methods (BEM). In this paper for wind blade design various factors such as tip loss, hub loss, drag coefficient, and wake were considered. The design process includes the selection of the wind turbine type and the determination of the blade airfoil, twist angle distribution along the radius, and chord length distribution along the radius. A parametric study that will determine if the optimized values of blade twist angle and chord length create the most efficient blade geometry. The 3-bladed, 5-bladed and 7-bladed rotor achieved maximum values of Cp 0.46, 0.5 and 0.48 at the tip speed ratio 7, 5 and 4 respectively. It was observed that using BEM theory, maximum Cp varied with strongly solidity and weakly with the blade number. The studies showed that the power coefficient increases upto blade number B = 5, while the blade number if increased above 5 then the power coefficient decreases at operating pitch angle equal to 3°. Highest Cp would have solidity between 4% to 6% for number of blade 3 and design point tip speed ratio of about "7". Highest Cp would have solidity ranging from 5% to 10% for number of blade 5 and 7 and design point tip speed ratio of about 5 and 4 respectively.

In this research article, a developed approach was introduced for the design and optimization of small wind turbine blades based on computational tools such as FAST and QBlade to address challenges in aerodynamic analysis, structural integrity, and power output prediction. A key focus is on optimizing airfoil selection based on lift-to-drag ratios, with the NACA4412 airfoil emerging as the most suitable choice for enhancing turbine performance. The optimization process includes a linearization approach for adjusting the chord and twist angles of the blade, which proved beneficial in streamlining the design. This approach led to notable improvements in the power coefficient across a range of rotational speeds, achieving an average increase of up to 8% and boosting power generation at a wind speed by 6.38%. These findings underscore the effectiveness of a targeted, systematic design optimization in enhancing turbine efficiency and output.

Analysis on aerodynamic performance of mine horizontal axis wind turbine with air duct based on breeze power generation

The development of wireless sensor network based on breeze power generation is of great significance to promote the development of the intelligent mine. According to the underground environment of coalmine, a small horizontal axis wind turbine with mine air duct was designed. The aerodynamic performance of the wind turbine was analyzed by constructing the three‐dimensional solid model of the wind turbine. The results show that under the condition of underground low wind speed. Outer basin: the air flow entering the air duct is accelerated and rectified, and the speed increases near the impeller. The pressure value at the front end of the blade is the largest and the pressure value at the rear end of the blade is the smallest. A certain range of negative pressure zone is formed at the rear end of the impeller, which is conducive to the operation of the wind turbine. After passing through the impeller, the speed of the air flow decreases and is the lowest near the impeller rotating shaft. Inner basin: the air flow speed gradually increases along the radial direction of the impeller center. The pressure at the front end of the blade is greater than the atmospheric pressure, which is conducive to facilitating the operation of the wind turbine. When the wind speed reaches the rated wind speed of the wind turbine, the power, torque, and output power of the wind turbine increase, which can provide effective power generation. Compared with other airfoils, NACA5505 airfoil has higher lift drag ratio and thrust coefficient. Compared with the wind turbine without air duct, the wind turbine with air duct has higher wind energy conversion and output power under the condition of low Reynolds number, which verifies the feasibility of the wind turbine with air duct.