scholarly journals Active control of wind turbines through varying blade tip sweep

2017 ◽  
Author(s):  
Αχιλλεύς Μπουλαμάτσης
Keyword(s):  
Active Control ◽  
Wind Turbines ◽  
Blade Tip ◽  
Lifting Line ◽  
Blade Element

Σε αυτή την ερευνητική εργασία παρουσιάζεται ένας πρωτότυπος τρόπος ελέγχου των ανεμογεννητριών οριζόντιου άξονα. Η ιδέα αυτή, αναφέρεται σε πτερύγια ανεμογεννήτριας μεταβλητής γωνίας οπισθόκλισης των ακροπτερύγιων τους, τα οποία έχουν την ικανότητα να περιστρέφονται συλλογικά (κίνηση εντός επιπέδου περιστροφής του ρότορα) γύρω από έναν άξονα που βρίσκεται επάνω στα πτερυγία. Το οπισθοκλινές ακροπτερύγιο μπορεί να είναι τμήμα του υπάρχοντος πτερυγίου με ενσωματωμένο μηχανισμό ή προέκταση αυτού. Η ιδέα αυτού του πρωτότυπου τρόπου ενεργού ελέγχου, έχει ως σκοπό την αύξηση της παραγώμενης ενέργειας σε συγκεκριμένες περιοχές λειτουργίας, τη μείωση των φορτίων κόπωσης των πτερυγίων καθώς και των υψηλών φορτίων κατά τη διάρκεια μίας ριπής ανέμου που διέρχεται από την ανεμογεννήτρια, μέσω της μεταβολής της γωνίας οπισθόκλισης των ακροπτερυγίων του ρότορα. Η έρευνα διεξάγεται με ένα κατάλληλα τροποποιημένο μοντέλο βασισμένο στη θεωρία Blade Element Momentum (BEM) ώστε να λαμβάνεται υπόψη η επίδραση του οπισθοκλινούς ακροπτερυγίου και η τροποποίηση αυτή βασίστηκε στα αποτελέσματα που προκύπτουν από ένα αντίστοιχο μοντέλο βασισμένο στη θεωρία Lifting Line. Τα αποτελέσματα από το τελευταίο μοντέλο συγκρίθηκαν επίσης με αποτελέσματα που προέκυψαν από αντίστοιχα μοντέλα υπολογιστικής ρευστομηχανικής (CFD) και επιπλέον έγινε προσπάθεια επιτάχυνσης των υπολογισμών (με χρήση CUDA platform) που εκτελούνται εντός του μοντέλου (Lifting Line) πριν αυτό χρησιμοποιηθεί ως σημείο αναφοράς για την τροποποίηση του μοντέλου BEM. Οι προσομοιώσεις αφορούν την 5MW NREL ανεμογεννήτρια αναφοράς που ενσωματώνει ένα κατάλληλο ελεγκτή και τα πρώτα αποτελέσματα δείχνουν ωφέλιμη συμπεριφορά σε όλες τους τομείς που μελετήθηκε η επίδρασή του.

A comprehensive comparative investigation of the Lifting Line Theory and Blade Element Momentum Theory applied to small wind turbines

2021 ◽  
pp. 1-25
Author(s):  
K.A.R. Ismail ◽  
Willian Okita
Keyword(s):  
Wind Turbines ◽  
Power Coefficient ◽  
Computational Time ◽  
Local Flow ◽  
Small Wind Turbines ◽  
Wake Effects ◽  
Line Theory ◽  
Lifting Line ◽  
Lifting Line Theory ◽  
Blade Element

Abstract Small wind turbines 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 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 wind turbines 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 lifting line theory provides more precise results and more information on the local flow over the rotor blades.

scholarly journals Active control of wind turbines through varying blade tip sweep

2019 ◽  
Vol 131 ◽  
pp. 25-36 ◽  
Author(s):  
Achilles M. Boulamatsis ◽  
Thanasis K. Barlas ◽  
Herricos Stapountzis
Keyword(s):  
Active Control ◽  
Wind Turbines ◽  
Blade Tip

Implementation of Computational Methods to Obtain Accurate Induction Factors for Offshore Wind Turbines

2014 ◽  
Author(s):  
Anand Bahuguni ◽  
Krishnamoorthi Sivalingam ◽  
Peter Davies ◽  
Johan Gullman-Strand ◽  
Vinh Tan Nguyen
Keyword(s):  
Wind Turbines ◽  
Lift Coefficient ◽  
Offshore Wind ◽  
Cfd Simulations ◽  
Sea State ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Blade Tip ◽  
Computational Fluid Dynamics Cfd ◽  
Blade Element

Most of the wind turbine analysis softwares widely being used in the market are based on the Blade Element Momentum method (BEM). The two important parameters that the BEM codes calculate are the axial and the tangential induction factors. These factors are calculated based on the empirical blade lift coefficient Cl and drag coefficient Cd along with some loss/correction functions to account for the losses near the blade tip and the hub. The current study focusses on verifying the values of induction factors using Computational Fluid Dynamics (CFD) simulations for floating offshore wind turbines at a selected sea state. The study includes steady state calculations as well as transient calculations for pitching motions of the turbine due to waves. The NREL FAST software is used to set the simulation scenarios according to OC3 Phase IV cases. The blades are divided a number of elements in CFD calculations and the data are extracted at individual elements to have an exact comparison with the BEM based calculations.

scholarly journals Numerical Simulations of Novel Conning Designs for Future Super-Large Wind Turbines

2020 ◽  
Vol 11 (1) ◽  
pp. 147
Author(s):  
Zhenye Sun ◽  
Weijun Zhu ◽  
Wenzhong Shen ◽  
Qiuhan Tao ◽  
Jiufa Cao ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Cone Angle ◽  
Angle Of Attack ◽  
Normal Direction ◽  
Velocity Decomposition ◽  
New Concepts ◽  
Blade Tip ◽  
Tip Position ◽  
Large Wind ◽  
Lower Angle

In order to develop super-large wind turbines, new concepts, such as downwind load-alignment, are required. Additionally, segmented blade concepts are under investigation. As a simple example, the coned rotor needs be investigated. In this paper, different conning configurations, including special cones with three segments, are simulated and analyzed based on the DTU-10 MW reference rotor. It was found that the different force distributions of upwind and downwind coned configurations agreed well with the distributions of angle of attack, which were affected by the blade tip position and the cone angle. With the upstream coning of the blade tip, the blade sections suffered from stronger axial induction and a lower angle of attack. The downstream coning of the blade tip led to reverse variations. The cone angle determined the velocity and force projecting process from the axial to the normal direction, which also influenced the angle of attack and force, provided that correct inflow velocity decomposition occurred.

scholarly journals Accurate loads and velocities on low solidity wind turbines using an improved Blade Element Momentum model

2020 ◽  
Author(s):  
Yassine Ouakki ◽  
Abdelaziz Arbaoui
Keyword(s):  
Drag Force ◽  
Wind Turbines ◽  
Solution Method ◽  
Turbine Blades ◽  
Accurate Prediction ◽  
Accurate Estimation ◽  
Complex Nature ◽  
Momentum Theory ◽  
Far Wake ◽  
Blade Element

Abstract. The accurate prediction of loadings and velocities on a wind turbine blades is essential for the design and optimization of wind turbines rotors. However, the classical BEM still suffer from an inaccurate prediction of induced velocities and loadings, even if the classical correction like stall delay effect and tip loss correction are used. For low solidity rotors, the loadings are generally over-predicted in the tip region, since the far wake expansion is not accurately accounted for in the one-dimensional (1D) momentum theory. The 1D dimensional momentum theory supposes that the far wake axial induction is equal to twice the axial induction in the rotor plane, which results in an under-estimation of the axial induction factor in the tip region. Considering the complex nature of the flow around a rotating blade, the accurate estimation of 3D effects is still challenging, since most stall delay models still often tend to under-predict or over-predict the loadings near the root region. As for the solution method for the classical BEM equation, the induced velocities are computed accounting for the drag force. However, according to the Kutta-Joukowski theorem, the induced velocities on a blade element are only created by lift force. Accounting for drag force when solving the BEM will result in an over-estimation of the axial induction factor, while the tangential induction factor is under-estimated. To improve the accuracy of the BEM method, in this paper, the 1D momentum theory is corrected using a new far wake expansion model to take into account the radial flow effect. The blade element theory is corrected for three-dimensional effects through an improved stall delay model. An improved solution method for the BEM equations respecting the Kutta-Joukowski theorem is proposed. The improved BEM model is used to estimate the aerodynamic loads and velocities on the National Renewable Energy Laboratory Phase VI rotor blades. The results of this study show that the proposed BEM model gives an accurate prediction of the loads and velocities compared to the classical BEM model.

scholarly journals Modeling and simulation of forces applied to the horizontal axis wind turbine rotors by the vortex method coupled with the method of the blade element

2021 ◽  
Vol 12 (1) ◽  
pp. 413
Author(s):  
Ibtissem Barkat ◽  
Abdelouahab Benretem ◽  
Fawaz Massouh ◽  
Issam Meghlaoui ◽  
Ahlem Chebel
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Farms ◽  
Vortex Method ◽  
Operating Conditions ◽  
Horizontal Axis ◽  
Rotor Blades ◽  
Good Representation ◽  
Horizontal Axis Wind Turbine ◽  
Blade Element

This article aims to study the forces applied to the rotors of horizontal axis wind turbines. The aerodynamics of a turbine are controlled by the flow around the rotor, or estimate of air charges on the rotor blades under various operating conditions and their relation to the structural dynamics of the rotor are critical for design. One of the major challenges in wind turbine aerodynamics is to predict the forces on the blade as various methods, including blade element moment theory (BEM), the approach that is naturally adapted to the simulation of the aerodynamics of wind turbines and the dynamic and models (CFD) that describes with fidelity the flow around the rotor. In our article we proposed a modeling method and a simulation of the forces applied to the horizontal axis wind rotors turbines using the application of the blade elements method to model the rotor and the vortex method of free wake modeling in order to develop a rotor model, which can be used to study wind farms. This model is intended to speed up the calculation, guaranteeing a good representation of the aerodynamic loads exerted by the wind.

scholarly journals Combined Blade-Element Momentum—Lifting Line Model for Variable Loads on Downwind Turbine Towers

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2521 ◽  
Author(s):  
Shigeo Yoshida
Keyword(s):  
Fluid Dynamics ◽  
Cost Reduction ◽  
Momentum Theory ◽  
Impulsive Loads ◽  
Line Theory ◽  
Lifting Line ◽  
Large Wind ◽  
Lifting Line Theory ◽  
Tower Shadow ◽  
Blade Element

Downwind rotors are a promising concept for multi-megawatt scale large wind turbines due to their advantages in safety and cost reduction. However, they have risks from impulsive loads when one of the blades passes across the tower wake, where the wind speed is lower and locally turbulent. Although the tower shadow effects on the tower loads have been discussed in former studies, there is currently no appropriate model for the blade-element and momentum theory so far. This study formulates the tower shadow effects on the tower load variation induced by blades using the lifting line theory, which does not require any empirical parameters. The method is verified via computational fluid dynamics for a 2 MW(megawatt), 3-bladed downwind turbine. The amplitude and the phase of the variation are shown to be accurate in outboard sections, where the rotor-tower clearance is large (>3.0 times of the tower diameter) and the ratio of the blade chord length is small (<0.5 times of the tower diameter), in both of rated and cut-out conditions.

scholarly journals Evaluation of Tip Loss Corrections to AD/NS Simulations of Wind Turbine Aerodynamic Performance

2019 ◽  
Vol 9 (22) ◽  
pp. 4919 ◽  
Author(s):  
Wei Zhong ◽  
Tong Guang Wang ◽  
Wei Jun Zhu ◽  
Wen Zhong Shen
Keyword(s):  
Wind Turbine ◽  
Wind Farm ◽  
Relative Difference ◽  
Superior Performance ◽  
Navier Stokes ◽  
Special Focus ◽  
Actuator Disc ◽  
Blade Tip ◽  
Blade Loads ◽  
Blade Element

The Actuator Disc/Navier-Stokes (AD/NS) method has played a significant role in wind farm simulations. It is based on the assumption that the flow is azimuthally uniform in the rotor plane, and thus, requires a tip loss correction to take into account the effect of a finite number of blades. All existing tip loss corrections were originally proposed for the Blade-Element Momentum Theory (BEMT), and their implementations have to be changed when transplanted into the AD/NS method. The special focus of the present study is to investigate the performance of tip loss corrections combined in the AD/NS method. The study is conducted by using an axisymmetric AD/NS solver to simulate the flow past the experimental NREL Phase Ⅵ wind turbine and the virtual NREL 5MW wind turbine. Three different implementations of the widely used Glauert tip loss function F are discussed and evaluated. In addition, a newly developed tip loss correction is applied and compared with the above implementations. For both the small and large rotors under investigation, the three different implementations show a certain degree of difference to each other, although the relative difference in blade loads is generally no more than 4%. Their performance is roughly consistent with the standard Glauert correction employed in the BEMT, but they all tend to make the blade tip loads over-predicted. As an alternative method, the new tip loss correction shows superior performance in various flow conditions. A further investigation into the flow around and behind the rotors indicates that tip loss correction has a significant influence on the velocity development in the wake.

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