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.

A Study of Power Production and Noise Generation of a Small Wind Turbine for an Urban Environment

2017 ◽  
Author(s):  
Andrew Hays ◽  
Kenneth Van Treuren
Keyword(s):  
Urban Environment ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Power Production ◽  
Small Scale ◽  
Momentum Theory ◽  
Small Wind Turbines ◽  
Noise Measurements ◽  
Utility Scale ◽  
Blade Element

Wind energy has had a major impact on the generation of renewable energy. While most research and development focuses on large, utility-scale wind turbines, a new application is in the field of small wind turbines in the urban environment. A major design challenge for these urban wind turbines is the noise generated during operation. This study examines the power production and the noise generated by two small-scale wind turbines tested in a small wind tunnel. Both rotors were designed using the Blade-Element Momentum Theory and either the NREL S823 or the Eppler 216 airfoils. Point noise measurements were taken using a 1/4” microphone at three locations downstream of the turbine: 16% of the diameter (two chord lengths), 50% of the diameter, and 75% of the diameter. At each horizontal location downstream of the turbine, a vertical traverse was performed to analyze the sound pressure level from the tip of the turbine blades down to the hub. The rotor designed with the Eppler 216 airfoil showed a 9% increase in power production and decrease of up to 7 dB(A).

A Study of Power Production and Noise Generation of a Small Wind Turbine for an Urban Environment

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Andrew Hays ◽  
Kenneth W. Van Treuren
Keyword(s):  
Urban Environment ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Power Production ◽  
Small Scale ◽  
Momentum Theory ◽  
Small Wind Turbines ◽  
Noise Measurements ◽  
Utility Scale ◽  
Blade Element

Wind energy has had a major impact on the generation of renewable energy. While most research and development focuses on large, utility-scale wind turbines, a new application is in the field of small wind turbines for the urban environment. A major design challenge for urban wind turbines is the noise generated during operation. This study examines the power production and the noise generated by two small-scale wind turbines tested in a small wind tunnel. Both rotors were designed using the blade-element momentum theory using either the NREL S823 or the Eppler 216 airfoils. Point noise measurements were taken using a microphone at three locations downstream of the turbine: 16% of the diameter (two chord lengths), 50% of the diameter, and 75% of the diameter. At each location downstream of the turbine, a vertical traverse was performed to analyze the sound pressure level (SPL) from the tip of the turbine blades down to the hub. The rotor designed with the Eppler 216 airfoil showed a 9% increase in power production and decrease of up to 7 dB(A).

Performance of an H-Darrieus in the Skewed Flow on a Roof1

2003 ◽  
Vol 125 (4) ◽  
pp. 433-440 ◽  
Author(s):  
Sander Mertens ◽  
Gijs van Kuik ◽  
Gerard van Bussel
Keyword(s):  
Wind Turbines ◽  
Power Output ◽  
Vertical Axis ◽  
Horizontal Wind ◽  
Energy Yield ◽  
Wind Environment ◽  
Momentum Theory ◽  
Vertical Axis Wind Turbines ◽  
Flat Roof ◽  
Blade Element

Application of wind turbines on roofs of higher buildings is a subject of increasing interest. However, the wind conditions at the roof are complex and suitable wind turbines for this application are not yet developed. This paper addresses both issues: the wind conditions on the roof and the behavior of a roof-located wind turbine with respect to optimized energy yield. Vertical Axis Wind Turbines (VAWTs) are to be preferred for operation in a complex wind environment as is found on top of a roof. Since the wind vector at a roof is not horizontal, wind turbines on a roof operate in skewed flow. Thus the behavior of an H-Darrieus (VAWT) is studied in skewed flow condition. Measurements showed that the H-Darrieus produces an increased power output in skewed flow. The measurements are compared with a model based on Blade Element Momentum theory that also shows this increased power output. This in contradiction to a HAWT in skewed flow which suffers from a power decrease. The paper thus concludes that due to this property an H-Darrieus is preferred above the HAWT for operation on a flat roof of higher buildings.

Inclusion of a Simple Dynamic Inflow Model in the Blade Element Momentum Theory for Wind Turbine Application

2014 ◽  
Author(s):  
Xiaomin Chen ◽  
Ramesh Agarwal
Keyword(s):  
Steady State ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Phase Iii ◽  
Speed Ratio ◽  
Horizontal Axis Wind Turbine ◽  
Bem Theory ◽  
Blade Element

It is well established that the power generated by a Horizontal-Axis Wind Turbine (HAWT) is a function of the number of blades B, the tip speed ratio λr (blade tip speed/wind free-stream velocity) and the lift to drag ratio (CL/CD) of the airfoil sections of the blade. The previous studies have shown that Blade Element Momentum (BEM) theory is capable of evaluating the steady-state performance of wind turbines, in particular it can provide a reasonably good estimate of generated power at a given wind speed. However in more realistic applications, wind turbine operating conditions change from time to time due to variations in wind velocity and the aerodynamic forces change to new steady-state values after the wake settles to a new equilibrium whenever changes in operating conditions occur. The goal of this paper is to modify the quasi-steady BEM theory by including a simple dynamic inflow model to capture the unsteady behavior of wind turbines on a larger time scale. The output power of the wind turbines is calculated using the improved BEM method incorporating the inflow model. The computations are performed for the original NREL Phase II and Phase III turbines and the Risoe turbine all employing the S809 airfoil section for the turbine blades. It is shown by a simple example that the improved BEM theory is capable of evaluating the wind turbine performance in practical situations where operating conditions often vary in time.

CALCULATION OF THE UNSTEADY AIRLOADS ON WIND TURBINE BLADES UNDER YAWED FLOW

2009 ◽  
Vol 23 (03) ◽  
pp. 493-496 ◽  
Author(s):  
HAI-QING SI ◽  
TONG-GUANG WANG
Keyword(s):  
Wind Turbine ◽  
Turbine Blades ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Dynamic Stall ◽  
Dependent Manner ◽  
Wind Turbine Blades ◽  
Blade Element Momentum Theory ◽  
Momentum Theory ◽  
Blade Element

A dynamic stall model is coupled with the blade element momentum theory to calculate the cyclic variation of the aerodynamic characteristics of the wind turbine in yawed flow. In the dynamic stall model, unsteady effects under attached flow conditions are simulated by the superposition of indicial aerodynamic responses. The movement of the unsteady flow separation point is related to the static separation based on the Kirchhoff flow model via a deficiency function, in which the unsteady boundary layer response and the leading edge pressure response are taken into consideration. The induced vortex force and the associated pitching moment are represented empirically in a time-dependent manner during dynamic stall. The required input of the inflow velocity and incidence to the dynamic stall model is calculated using the improved blade element momentum theory. The calculated results are compared well with the NREL UAE Phase VI experimental data. For completeness, possible factors causing the difference between calculated and experimental results are analyzed and discussed in detail in this paper.

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