S809 Airfoil Research Articles

풍차 날개의 틈새에 패들휠을 사용하는 새로운 능동 유동제어 방법에 대한 유동해석

In the following years, the wind energy industry will maintain its surge during the last few decades. Meanwhile, horizontal axis wind turbines (HAWT) are the most prominent one among other wind turbines. Accordingly, enhancing blade aerodynamic performance should be the main part of study over this type of turbines. For this purpose, various active and passive flow control methods are being extensively investigated. Investigating new hybrid method is the main aim of this paper. Therefore, in this present study a novel idea, that uses a paddle wheel which is located inside the split, is investigated. This new configuration is based on the split method and the rotation of a paddle wheel that provides pulsatile flow inside the split. The flow then gets injected into the bulk flow over the airfoil, causing hybrid flow control effects. Optimized split geometry of S809 airfoil has been selected and then a paddle wheel is placed inside the split. First, the effect of split width on passing flow and separation zone was investigated. Second, the effect of rotational speed of the paddle is discussed. To this end, 2D CFD simulations using SST-k-ω turbulence model have been performed. The simulations have been conducted for a wide range of angles of attack (AOA). The results are discussed in the form of aerodynamics force coefficients as well as streamlines to compare the size of the separation area at higher angles of attack.

Design and aerodynamic performance analysis of a finite span double-split S809 configuration for passive flow control in wind turbines and comparison with single-split geometries

With the previous knowledge of the effectiveness of single-split blades, questions arise about the effectiveness of a double-split configuration on horizontal axis wind turbine. To shed light on this question, a 3-D double-split finite-span configuration with S809 airfoil profile is designed based on the results of unsteady DES simulations of two families of single-split configurations. Firstly, the two 3-D single-split families with four different values of split width are simulated at angles of attack (AOA) up to 25°. Secondly, a finite span double-split model is designed based on the single-split geometries with the highest aerodynamic performances. It has been found that the double-split configuration had the poorest performance for 0°<AOA<17°; however, at 17°<AOA<22°, the double-split model showed the highest performance. Analyzing the time-averaged streamlines showed that excessive injected flow at low AOAs as well as the formation of separation bubbles inside the split channel were two main negative factors that severely reduced the performance of the double-split geometry. Also, findings revealed that using optimum cases of single-split geometry does not result in an optimum double-split geometry. Lastly, considering all findings, a conceptual selective (controlled) flow control method that led to a considerable increase in the aerodynamic performance of the double-split geometry has been proposed and discussed.

Research and Development of a Small-Scale Icing Wind Tunnel Test System for Blade Airfoil Icing Characteristics

In order to study the icing mechanism and anti-icing technology, a small low-speed reflux icing wind tunnel test system was designed and constructed. The refrigeration system and spray system were added to the small reflux low-speed wind tunnel to achieve icing meteorological conditions. In order to verify the feasibility of the test system, the flow field uniformity, temperature stability, and liquid water content distribution of the test section were tested and calibrated. On this basis, the icing tests of an aluminium cylinder, an NACA0018 airfoil, and an S809 airfoil were carried out, and the two-dimensional ice shape obtained by the test was compared with the two-dimensional ice shape obtained by the numerical simulation software. The results show that in the icing conditions and icing time studied, the parameters of the test system are stable, and the experimental ice shape is consistent with the simulated ice shape, which can meet the needs of icing research.

Flow control of a stalled S809 airfoil using an oscillating micro-cylinder at different angles of attack

The flow control effects on the S809 airfoil produced by an oscillating micro-cylinder placed upstream of the airfoil suction surface were investigated using numerical simulations at Reynold number of 1×106 and high angles of attack (α) range from 20° to 24°. The oscillating mode and initial position of the micro-cylinder are two main parameters considered in this paper. The numerical results suggest that at the start of a heavy stall angle of attack (α < 22°), flow separation can be suppressed when the optimum oscillating mode and initial position of the micro-cylinder were given. However, once the airfoil is confronted to heavy stall angles of attack (α > 22°), its aerodynamic performance could only be lightly improved or even deteriorated because of the strong and large adverse separation which could not be controlled effectively by the small oscillating cylinder. It was also found that a better control effect can be obtained when the initial position of the cylinder was set adjacent to the separation point compared with that placed near the leading edge at α = 21°. Furthermore, our results also showed that higher dimensionless oscillating amplitudes and a larger frequency can obtain a higher lift-to-drag ratio when the micro-cylinder was placed at optimal initial position.

Effects of Micro-Tab on the Lift Enhancement of Airfoil S-809 with Trailing-Edge Flap

Recently, the Trailing-Edge Flap with Micro-Tab (TEF with Micro-Tab) has been exploited to enhance the performance of wind turbine blades. Moreover, it can also be used to generate more lift and delay the onset of stall. This study focused mostly on the use of TEF with Micro-Tab in wind turbine blades using NREL’s S-809 as a model airfoil. In particular, the benefits generated by TEF with Micro-Tab may be of great interest in the design of wind turbine blades. In this paper, an attempt was made to evaluate the influence of TEF with Micro-Tab on the performance of NREL’s S-809 airfoils. Firstly, a computational fluid dynamics (CFD) model for the airfoil NREL’s S-809 was established, and validated by comparison with previous studies and wind tunnel experimental data. Secondly, the effects of the flap position (H) and deflection angle (αF) on the flow behaviors were investigated. As a result, the effect of TEF on air-flow behavior was demonstrated by augmenting the pressure coefficient at the lower surface of the airfoil at flap position 80% chord length (C) and αF = 7.5°. Thirdly, the influence of TEF with Micro-Tab on the flow behaviors of the airfoil NREL’s S-809 was studied and discussed. Different Micro-Tab positions and constant TEF were examined. Finally, the effects of TEF with Micro-Tab on the aerodynamic characteristics of the S-809 with TEF were compared. The results showed that an increase in the maximum lift coefficient by 25% and a delay in the air-flow stall were accomplished due to opposite sign vortices, which was better than the standard airfoil and S-809 with TEF. Therefore, it was deduced that the benefits of TEF with Micro-Tab were apparent, especially at the lower surface of the airfoil. This particularly suggests that the developed model could be used as a new trend to modify the designs of wind turbine blades.

Aerodynamic Shape Optimization of NREL S809 Airfoil for Wind Turbine Blades Using Reynolds-Averaged Navier Stokes Model—Part II

Sustainability has become one of the most significant considerations in everyday work, including energy production. The fast-growing trend of wind energy around the world has increased the demand for efficient and optimized airfoils, which has paved the way for energy harvesting systems. The present manuscript proposes an aerodynamically optimized design of the well-known existing NREL S809 airfoil for performance enhancement of the blade design for wind turbines. An integrated code, based on a genetic algorithm, is developed to optimize the asymmetric NREL S809 airfoil by class shape transformation (CST) and the parametric section (PARSEC) parameterization method, analyzing its aerodynamic properties and maximizing the lift of the airfoil. The in-house MATLAB code is further incorporated with XFOIL to calculate the coefficient of lift, coefficient of drag and lift-to-drag ratio at angles of attack of 0° and 6.2° by the panel technique and validated with National Renewable Energy Laboratory (NREL) experimental results provided by The Ohio State University (OSU). On the other hand, steady-state CFD analysis is performed on an optimized S809 airfoil using the Reynolds-averaged Navier–Stokes (RANS) equation with the K–ω shear stress transport (SST) turbulent model and compared with the experimental data. The present method shows that the optimized airfoil by CST is predicted, with an increment of 11.8% and 9.6% for the lift coefficient and lift-to-drag ratio, respectively, and desirable stability parameters obtained for the design of the wind turbine blades. These characteristics significantly improve the overall aerodynamic performance of new optimized airfoils. Finally, the aerodynamically improved results are reported for the design of the NREL Phase II, Phase III and Phase VI HAWT blades.

Numerical investigation into rotational augmentation with passive vortex generators on the NREL Phase VI blade

Passive vortex generators (VGs) have been widely used on wind turbines to improve the aerodynamic power. Nevertheless, most studies of VGs are conducted on flat plates and airfoils rather than rotating blades. The effect of VGs on rotational blade flow therefore remains unclear. This paper presents a comparative study between the NREL S809 airfoil flow and NREL Phase VI blade flow, to highlight rotational augmentation with VGs. There are 36 pairs of rectangular VGs installed at about 20% c between 25% and 50% spans of the blade. Fully-resolved RANS simulations are used to identify the airfoil and blade flow characteristics with VGs. Although VGs greatly increase the maximum lift coefficient of airfoil by almost 60%, they cause unexpected decreases in aerodynamic forces on the inboard blade. This is mainly because VGs can reduce the radial flow and thus undermine rotational augmentation. Furthermore, increasing VG size amplifies the VG effect on radial flow and enlarges the separation bubble at 30% span from 43% c to 57% c in height. Positioning VGs in a skewed layout, however, effectively diminishes this negative VG effect and reduces the separation bubble height to 28% c. These findings indicate a huge difference between the airfoil flow and blade flow with VGs due to rotational effects. This work might deepen the understanding of rotational augmentation with VGs on a rotating blade.

Dynamic stall of the wind turbine airfoil and blade undergoing pitch oscillations: A comparative study

Dynamic stall significantly causes the unsteady aerodynamic loads on horizontal axis wind turbines. However, many studies are about dynamic stall of 2D airfoils rather than 3D rotating blades. The 3D dynamic stall is therefore still poorly understood and also challenging to predict accurately. This paper presents comparative analyses of dynamic stall among the 2D airfoil, 3D non-rotating blade and 3D rotating blade undergoing sinusoidal pitch oscillations. The parameters of 2 radial locations and 11 pitch conditions are also studied. All 3D aerodynamic responses come from the NREL Phase VI experiment. URANS simulations are used to predict the 2D aerodynamic responses of NREL S809 airfoil. Rotational augmentation is found to make the key difference between 2D airfoil flow and 3D blade flow. Rotational augmentation effectively suppresses the extension of separated flow during the upstroke process, and significantly accelerates the flow reattachment during the downstroke process. The onset of dynamic stall is therefore delayed with the maximum lift coefficient increased by 46%. The aerodynamic hysteresis intensity is also greatly reduced by 61%. Increasing the mean angle of attack (AOA), AOA amplitude and reduced frequency can further delay the onset of dynamic stall. On the other hand, rotational augmentation may unexpectedly produce a negative aerodynamic pitch damping and cause stall flutter on the inboard blade. Increasing AOA amplitude could reduce this negative damping and improve the torsional aeroelastic stability. This work might deepen the understanding of 3D dynamic stall with rotational augmentation on wind turbines.

Wind Turbine Blade Design Optimization using OpenFOAM and DAKOTA software

Owing to the fast development in the energy field, the demands are increasing to improve energy efficiency of wind turbine. In order to produce more efficient, sustainable-clean energy, accurate prediction of wind turbine design parameters provide to work the system efficiency at the maximum level. So, many research to determine wind turbine characteristics have been conducted by the researchers with different methods: theoretical analysis, experiment, numerical simulation... One of the main research subjects of wind turbines is blades. The wind blades are considered as the most important and expensive part in the wind turbine. The design optimization of the blades is the most important stage to maximize efficiency production. Aerodynamic characteristics of the blades are critical components that have a large influence on the performance of the turbine. So, the authors built an optimal model of aerodynamic characteristics through maximizing lift coefficient (Cl) and the lift to drag ratio. The lift to drag ratio is used to express the relation between lift and drag, it is determined by dividing the Cl by the drag coefficient (Cd). This value can be maximized by optimizing the blade shape. In this paper, a method of optimizing shape by combining computational fluid dynamics (CFD) and genetic algorithms (GA) is presented. Firstly, an S809 airfoil which is frequently used in wind turbines will be selected as the initial shape by a list of control points and then the lift and drag coefficients of this airfoil were determined using CFD. Next, the shape of the airfoil will be automatically changed by moving the control point through the GA method by Dakota (Design and Analysis toolKit for Optimization and Terascale Applications) software. The final shape that the lift to drag ratio for the optimal value will be found through a number of loops. The simulation results were validated by comparison with articles of Agarwal. [1] and Ritlop [3]. The main contribution of this paper is that the optimal model for predicting aerodynamic characteristics is built. Furthermore, the present study also points out the possible further research directions of optimizing the wind turbine so as to help researchers in the field develop more effective wind turbine designs according to geographical conditions and user needs at Viet Nam.

Numerical Investigation of the Aerodynamic Performance of S809 Airfoil

Numerical Investigation of the Aerodynamic Performance of S809 Airfoil

Probabilistic study of S809 airfoil for wind turbine blade

Probabilistic study of S809 airfoil for wind turbine blade

Desain Turbin Angin Horisontal untuk Area Kecepatan Angin Rendah dengan Airfoil S826

This research aims to determine performance of turbine rotor performance with a single rotor blade model with a diameter of 0.6 m that has been developed by NORCOWE, while for turbine rotor blades used is the NREL S826 airfoil series. The wind turbines are operated at wind speed intervals of 1-5 m / s. This parameter will also present data in the form of the optimal point of wind turbine rotation and rotor rotation speed. The pitch angles used are 25 °, 30 °, and 35 °. The pitch angle that affects the value of the ideal rotational speed with the highest optimization for the horizontal airfoil turbine S826 is 30 ° with a wind speed of 5 m / s and a rotation of 570 RPM. This is because the greater the pitch angle of the installation, the easier it will be to experience speed trimming but is vulnerable to too large an angle of attack that causes a stall.

The influence of freestream turbulence on the temporal pressure distribution and lift of an airfoil

To gain insight on how freestream turbulence (FST) affects the aerodynamics of an airfoil in a systematic manner, the present study investigates a NREL S826 airfoil subjected to seven different incoming flows with varying degrees of FST. The Reynolds number was held at Rec ​= ​4.0 ​× ​105, while the turbulence intensity (Ti) was varied between 0.4% and 5.4%. An increase in Ti increases the maximum lift while having negligible effects on the stall angle. The lift slope in the linear region also generally increased with higher Ti. The latter observation contrasts with some earlier studies, and incoming flow homogeneity is a potential contributing factor to the differences seen here. Periodic pressure fluctuations are seen in the computed lift time-series signal when Ti is between 1% and 2% and the airfoil is operating in the linear region. These fluctuations arise from surface pressure oscillations that are likely excited by the relatively low incoming Ti. The overall effect is a reduction in the time-averaged lift under these operating conditions. At higher Ti, more energetic boundary layers develop over the airfoil’s suction side and the effect of these periodic pressure fluctuations is suppressed, leading to an increase in the produced lift.

Aerodynamic performance improvement using a micro-cylinder as a passive flow control around the S809 airfoil

Aerodynamic performance improvement of airfoilsis the first step towards enhancement ofthe wind turbine performance in electricity generation and energy conversion inrenewable energy applications. The flow behavioraround wind turbine blades profilecan be improved by introducing active and/or passive flow controls. This work numerically describes the impact of adding micro-cylinder, as a passive flow control around S809 airfoil, on aerodynamic performance under various operating conditions. A suitable combination of flow analysis and optimization technique has been used in the current work.The numerical simulation has been performed using ANSYSFluent 18.2 software. The airfoil was numerically analysed in flow atReynolds number of 106; aerodynamic coefficients (lift and drag coefficients) at different angle of attacks were validated with the experimental data reported by Somers in NREL. The Response Surface Method (RSM) is applied to obtain the optimum position of micro-cylinder to achieve maximum lift to drag ratio. It has been found that the total aerodynamic forces are sensitive to the location of the micro-cylinder. A significant enhancement of lift to drag ratio can be achieved by adding micro-cylinder in front of S809 airfoil especially at high Reynolds number.

Input-output reduced-order modeling of unsteady flow over an airfoil at a high angle of attack based on dynamic mode decomposition with control

Due to the damage caused by stall flutter, the investigation and modeling of the flow over a wind turbine airfoil at high angles of attack are essential. Dynamic mode decomposition (DMD) and dynamic mode decomposition with control (DMDc) are used to analyze unsteady flow and identify the intrinsic dynamics. The DMDc algorithm is found to have an identification problem when the spatial dimension of the training data is larger than the number of snapshots. IDMDc, a variant algorithm based on reduced dimension data, is introduced to identify the precise intrinsic dynamics. DMD, DMDc and IDMDc are all used to decompose the data for unsteady flow over the S809 airfoil that are obtained by numerical simulations. The DMD results show that the dominant feature of a static airfoil is the adjacent shedding vortices in the wake. For an oscillating airfoil, the DMDc results may fail to consider the effect of the input and have an identification problem. IDMDc can alleviate this problem. The dominant IDMDc modes show that the intrinsic flow for the oscillating case is similar to the unsteady flow over the static airfoil. Moreover, the input–output model identified by IDMDc can give better predictions for different oscillating cases than the identified DMDc model.

Control of Dynamic Stall of an Airfoil by Using Synthetic Jet Technology

In this paper, the dynamic stall characteristics of the S809 airfoil have been numerically predicted, and the flow under dynamic stall condition has been controlled by introducing synthetic jet for enhancing the airfoil aerodynamic performance. In addition, experimental results have been adopted to validate the obtained numerical ones. The results show that the oscillation of the airfoil can delay the occurring of stall, and the stall angle of attack is increased from 9.5° to 13.1°. The introduction of synthetic jet can improve the lift coefficient of airfoil under dynamic stall conditions: The mean lift coefficient in a period of oscillation has been increased by 33%, and the drag coefficient has been reduced by 39%. Moreover, the stall angle of attack is increased from 13.1° to 16.2°. Therefore, the airfoil performance under dynamic stall condition could be greatly improved by the introduction of synthetic jet technology.

UTILIZACIÓN DEL MODELO DES, CON BASE EN EL MODELO DE TURBULENCIA SPALART-ALLMARAS EN EL ANÁLISIS DEL PERFIL S809

Este trabajo brinda el estudio numérico de las características aerodinámicas del perfil S809 para un número de Reynolds de 300000. El perfil S809 es uno de los perfiles más utilizados en aerogeneradores de baja potencia y bastante estudiado experimentalmente por varios autores. Para el estudio se utilizó el programa FLUENT del paquete ANSYS donde se seleccionó el modelo de turbulencia Spalart-Allmaras. Durante el estudio se utilizaron ángulos de ataque que variaron desde 0° hasta 15,2° determinándose los coeficientes de arrastre y sustentación para cada posición. El comportamiento aerodinámico numérico del perfil seleccionado presentó excelentes resultados cuando comparados con resultados experimentales reportados en la literatura. Se determinó que el modelo de turbulencia utilizado representa adecuadamente el proceso físico, pero a partir de un ángulo de ataque de 10,2° comienza a desviarse levemente de los resultados experimentales, lo que puede ser explicado debido al aumento de la turbulencia por el aumento del ángulo de ataque.

Characteristics and Effects of Laminar Separation Bubbles on NREL S809 Airfoil Using the γ - R e θ Transition Model

Understanding the characteristics and effects of the laminar separation bubbles (LSBs) is important in the aerodynamic design of wind turbine airfoils for maximizing wind turbine efficiency. In the present study, numerical simulations using the γ-Reθ transition model were performed to analyze the flow structure of LSBs around a 21% thick NREL S809 airfoil. The simulation results obtained from the γ-Reθ transition model and the standard k-ε model for the aerodynamic coefficients at various angles of attack (AoAs) were compared with the wind tunnel data acquired from the Delft University 1.8 m × 1.25 m low-turbulence wind tunnel. When the AoA increased, the bubble on the suction airfoil surface was found to move closer to the leading edge owing to an earlier laminar separation (LS). Furthermore, the transition onset (TO) points were shown to occur right after separation, thus causing an abrupt increase in turbulence intensity (TI) and forming different bubble extents with increasing AoAs. Consequently, the transition model-based approaches can provide a clear understanding of the characteristics and effects of the LSB on airfoil aerodynamic performance. The findings of this study can provide important insights into redesigning an airfoil with a reduced bubble length causing the improved aerodynamic performance.

Effects of blunt trailing-edge optimization on aerodynamic characteristics of NREL phase VI wind turbine blade under rime ice conditions

To reduce the adverse effects of the ice on aerodynamic characteristics, a new NREL Phase VI wind turbine blade which is suitable to rime ice environments is developed through the blunt trailing-edge optimization. The parametric control equations of blunt trailing-edge airfoil are established by adopting the airfoil profile integration theory and B-spline curve, and the curve fitting of the airfoil’s rime ice from LEWICE software is carried out using the linear interpolation algorithm with equidistant and equiangular step lengths. The S809 airfoil under rime ice conditions is optimized to maximize the lift coefficient by the particle swarm optimization (PSO) coupled with GAMBIT and FLUENT, and a NREL Phase VI blade is formed with the optimized airfoil S809-BT (with BT the blunt trailing-edge). The blade’s rime ice is obtained through using the polynomial fitting to deal with projection point coordinates of airfoils’ ice shapes in lagging and flapping surfaces, and the pressure coefficient, flow characteristics, torque and output power of icy sharp and blunt trailing-edge blades are investigated. The results indicate that in rime ice conditions, compared with those of sharp trailing-edge blade, the pressure difference and vortex size of blunt trailing-edge blade become larger, and the torque and output power increase by 4.36 %, 1.55 % and 2.88 % at v= 7 m/s, 15 m/s and 20 m/s, respectively. The research provides significant guidance for improving the aerodynamic performance of wind turbine blade considering the icing effects.

Numerical Investigation of Active Control of Boundary Layer Flow Around S809 Airfoil with Suction Method

Bu çalışmada, sınır tabaka akışı aktif kontrol yöntemlerinden biri olan, sınır tabakadan kanat içerisine hava emilmesi prensibine dayanan emme tekniği kullanılarak bir rüzgar türbini kanadının aerodinamik performansının arttırılması hedeflenmiştir. Emme işlemi daimi bir jet vasıtasıyla gerçekleştirilmiş, kanat modeli olarak rüzgar türbini uygulamalarında yaygın olarak kullanılan S809 kanat profili tercih edilmiştir. Çalışma parametreleri olarak, üç ayrı jet konumu (Ljet = 0.1c, 0.26c, 0.36c) ve üç ayrı jet oranı (Rjet = 0.1, 0.3, 0.5) seçilmiştir. Emme jeti genişliği sabit olup veter uzunluğunun %2.5’i kadar ve emme jeti açısı (θjet) bölgesel jet yüzeyine 90° olacak şekilde ayarlanmıştır. İki boyutlu türbülanslı akış için sayısal analiz; α = 15° hücum açısında ve Re = 106’da SST k-ω türbülans modeli kullanılarak gerçekleştirilmiştir. İlk olarak emme jeti konumunun etkisi, ardından en iyi sonucu veren emme jeti konumu seçilerek emme jeti oranının etkisi araştırılmıştır. Kanat profili etrafındaki akışa ait simülasyon sonuçları incelendiğinde, en iyi sonuç emme jeti konumu 0.36c (Jet-3) ve emme jeti oranı 0.5 olduğunda alınmıştır. Jet kullanılmadığı duruma göre CL/CD oranı 17.92’den 273.03’e yükselmiştir. Emme jeti ile kontrol yönteminin uygulanması ile kontrolsüz duruma göre Cl değeri yaklaşık olarak 1.211’den 1.8’e yükselmiş, Cd değeri ise 0.068’den 0.0066’ya düşmüştür.