Airfoil Optimization for Small Wind Turbines Using Multi Objective Genetic Algorithm

Review of aerodynamic developments on small horizontal axis wind turbine blade

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

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.

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.

The root region of small wind turbines experience low Reynolds number (Re) flow that makes it difficult to design airfoils that provide good aerodynamic performance and at the same time, provide structural strength. In the present work, a multi-objective genetic algorithm code was used to design airfoils that are suitable for the root region of small wind turbines. A composite Bezier curve with two Bezier segments and 16 control points (11 of them controlled) was used to parametrize the airfoil problem. Geometric constraints including suitable curvature conditions were enforced to maintain the airfoil thickness between 18% and 22% of chord and a trailing edge thickness of 3% of chord. The objectives were to maximize the lift-to-drag ratio for both clean and soiled conditions. Optimization was done by coupling the flow solver to a genetic algorithm code written in C++, at Re = 200,000 and for angles of attack of 4 and 10 degrees, as the algorithm was found to give smooth variation of lift-to-drag ratio within such a range. The best airfoil from the results was tested in the wind tunnel as well as using ANSYS-CFX. The experimental airfoil had a chord length of 75 mm and was provided with 33 pressure taps. Testing was done for both free and forced transition cases. The airfoil gave the highest lift-to-drag ratio at an angle of 6 degrees with the ratio varying very little between 4 degrees and 8 degrees. Forced transition at 8% of chord did not show significant change in the performance indicating that the airfoil will perform well even in soiled condition. Fixed trailing edge flaps (Gurney flaps) were provided right at the trailing edge on the lower surface. The lift and drag behavior of the airfoil was then studied with Gurney Flaps of 2% and 3% heights, as it was found from previous studies that flap heights of 1% or greater than 3% do not give optimum results. The flaps considerably improved the suction on the upper surface and also improved the pressure on the lower surface, resulting in a higher lift coefficient; at the same time, there was also an increase in the drag coefficient but it was less compared to the increase in the lift coefficient. The results indicate that Gurney flaps can be effectively used to improve the performance of thick trailing edge airfoils designed for the root region of small wind turbines.

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

Influence of downstream wake rotation ω, drag coefficient Cd and Prandtl’s tip losses Fi on the geometry and performance of rotor blade for a 2kW horizontal axis small scale wind turbine has been analytically analyzed. The objectives of the study are accomplished through Blade Element Momentum theory (BEMT). Analytical examination reveals that only the idealized blade exhibits maximum geometry and its performance closely follows Betz limit due to non-consideration of downstream wake rotation ω, drag coefficient Cd and Prandtl’s tip losses Fi. However, inclusion of the said losses drastically changes the blade shape and performance. The study showed that the average sectional chord ci and twist distribution θTi of the idealized blade reduced by 20.42% and 14.08% respectively and also the Coefficient of Power Cp of the idealized blade reduced nearly by 29.4% as a result of losses.

This paper aims to do blade design of a small horizontal axis wind turbine and perform wind tunnel test to conform its efficiency. In this research Bladecalculator, Pro/E and ANSYS/CFX are used to find the relationship between the blade rotating speed with torque. The analytical results of wind turbine completely match with that of test data. Comparison with data of generator, new design blade gets more power. The power of new design blades is about ten times as the original blades.

Bringing electricity to areas of difficult terrain is a complicated task, so it is convenient to generate power using local natural resources, such as wind, through a small horizontal-axis wind turbine (S-HAWT). However, at the rotor height of these wind turbines, the wind is often turbulent due to obstacles such as trees and buildings. For a turbine to function properly in these conditions, the action of the wind force on the rotor must be smoothed out by controlling the pitch angle. A commercial derivative-integral-proportional (PID)-type pitch controller works well when system dynamics are stable, but not when there are disturbances in the system. This paper proposes a hierarchical fuzzy logic controller (HFLC) to solve the nonlinear system effects produced by atypical winds. The methodology includes a statistical analysis of wind variability at the installation site, which determines the functions of belonging and its hierarchy. In addition, installing an anemometer in front of the turbine allows an advanced positioning of the blades in the presence of wind gusts. The algorithm was implemented in an S-HAWT, and a comparison was made to quantify the performance difference between the proposed control strategy and a conventional PID controller.

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.

Study on small wind turbine icing and its performance

The wind energy is deemed as one of the most durable energetic variants of the future because the wind resources are immense. Furthermore, one predicts that the small wind turbines will play a vital role in the urban environment. Unfortunately, the complexity and the price of pitch regulated small horizontal-axis wind turbines represent ones of the main obstacles to widespread the use in populated zones. Moreover, the energetic efficiency of small stall regulated wind turbines has to be high even at low and medium wind velocities because, usually the cities are not windy places. During the running stall regulated wind turbines, due to the extremely broad range of the wind velocity, the angle of attack can reach high values and some regions of the blade will show stall and post-stall behavior. This paper deals with stall and post-stall regimes because they can induce significant vibrations, fatigue and even the wind turbine failure.

<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>

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.

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.