NREL Phase VI Wind Turbine Research Articles

Computational Fluid Dynamics (CFD) Investigation of NREL Phase VI Wind Turbine Performance Using Various Turbulence Models

This study presents a detailed computational fluid dynamics (CFD) investigation into the aerodynamic performance of the NREL Phase VI wind turbine, focusing on torque and power generation under different turbulence models. The primary objective was to analyse the effect of various turbulence models and their responses in wind turbine torque generation. Furthermore, it also investigates the distance effect on wind velocity deficit. The research utilizes 2D and 3D simulations of the S809 airfoil and the full rotor, examining the predictive capabilities of the k-epsilon, k-omega, and k-omega SST turbulence models. The study incorporates both experimental validation and wake analysis using the Gaussian wake model to assess wind velocity deficits. Simulations were conducted for a wind speed range of (6–10 m/s), with results indicating that the k-epsilon model provided the closest match to experimental data, particularly at higher wind speeds within the targeted range. Even though k-epsilon results had better agreement when validated with experimental data, theoretically k-omega (SST) should perform better as it combines k-epsilon and k-omega advantages in predicting the flow regardless of its farness from the wall. However, in simulations using the k-omega (SST), the separation of flow and the shear stress transients were only visible at wind speeds of 10 m/s or higher. Wake effects, on the other hand, were found to cause significant velocity deficits behind the turbine, following an exponential decay pattern. The findings offer valuable insights into improving wind turbine performance through turbulence model selection and wake impact analysis, providing practical guidelines for future wind energy optimizations.

Investigation of NREL Phase VI wind turbine blade with different winglet configuration for performance augmentation

ABSTRACT A wind turbine blade’s winglet is predominantly used to reduce the induced drag generated by the blades and consequently improve the blade’s aerodynamic performance. The benchmark blade NREL Phase VI and all blades with the winglet were designed and simulated using CFD. Subsequently, the numerical model is validated against data from the NREL Phase VI experiment. In the first case, at a fixed winglet length of 0.09 m, the best results are obtained for sharp bent configurations when the winglet cant angle is 45° whereas for smooth bent configurations is at a 30° cant angle. Under the second scenario, ten winglets with different winglet heights, lengths, and cant angles and a simple linear tip extension are generated and tested numerically at wind speeds of 5, 7 and 9 m/s. Therefore, curving the tip to make a winglet shape of applicable configuration is definitely preferable to extending the tip straight.

An actuator line method for performance prediction of HAWTs at urban flow conditions: A case study of rooftop wind turbines

Blade-resolved numerical modeling of wind turbines at complex flow conditions are resource expensive due to large computational domains and extra-fine grid requirements. The Actuator Line Method (ALM) can significantly boost the simulation speed, providing acceptable accuracy and flow details. This study investigates the performance of NREL Phase VI wind turbine mounted over a high-rise building at nine different locations, providing practical illustrations of complicated flow situations. To demonstrate the superior capabilities of this method compared to the actuator disk model, two hub-heights are considered for mounting the wind turbine. Results showed that the power coefficient of the turbines with higher hub-height are close to the corresponding bare wind turbine. However, up to 52 % reduction was observed for the low hub-heights. Furthermore, variations of the bending moment experienced by the turbine's blade in a complete revolution are presented, which is a crucial factor affecting the fatigue life and structural stability of the wind turbine. Eventually, more in-depth discussions on the time-evolution of rotor performance at various locations are presented by illustrating the spanwise distributions of Angle-of-Attack histogram and its PSD diagram for the blade-1 of the wind turbine.

NREL Phase VI wind turbine blade tip with S809 airfoil profile winglet design and performance analysis using computational fluid dynamics

NREL Phase VI wind turbine blade tip with S809 airfoil profile winglet design and performance analysis using computational fluid dynamics

Numerical investigation of blade roughness impact on the aerodynamic performance and wake behavior of horizontal axis wind turbine

The prolonged operation of wind turbines in harsh offshore environments leads to deterioration and roughness accumulation on the blade surface. This roughness, particularly on the leading edge and other surfaces, can affect the laminar-to-turbulent transition, alter the flow characteristics in the turbine wake and turbulent boundary layer, and become critical for the accurate design and performance analysis of offshore horizontal axis wind turbines (HAWT). This study investigates the effects of blade surface roughness on the aerodynamic performance and wake evolution of the NREL Phase VI wind turbine rotor using the Reynolds-Averaged Navier-Stokes (RANS) technique. First, 2D simulations are validated against experimental data of the S809 airfoil. Then, full-scale 3D simulations of the complete turbine model are conducted with roughness effects to simulate natural conditions. The results show that surface roughness reduces the blade’s aerodynamic performance. The rough surface increases the boundary layer thickness, causing flow separation and turbulence, which decrease the lift generated by the blade and increase its drag, resulting in decreased overall blade performance. At higher wind speeds, surface roughness has a negligible effect on turbine performance due to flow separation at the leading edge. The analysis of surface roughness effects on the turbine wake flow indicates that blade roughness positively correlates with wake recovery, where the wake velocity recovers faster with an increase in roughness height.

A New Flow Control and Efficiency Enhancement Method for Horizontal Axis Wind Turbines Based on Segmented Prepositive Elliptical Wings

Flow separation occurs when wind turbines operate under large inflow conditions, which seriously affects the utilization of wind energy and reduces the output power of the blade. Therefore, a composite flow control configuration for horizontal axis wind turbines, founded on segmented prepositive elliptical wings, is proposed for efficiency enhancement. Taking a typical NREL Phase VI wind turbine as the prototype, its separation effect is evaluated by the CFD method. Then, starting from the improvement of the two-dimensional airfoil flow, the prepositive elliptic wing is designed according to the airfoil flow, and the optimal two-dimensional flow control configuration of the blade airfoil is obtained by simulation analysis. Finally, the two-dimensional configuration is extended to three-dimensional, and the aerodynamic characteristics of the blade before and after flow control are simulated and compared. The results show that, at wind speeds of 10~20 m/s, flow separation on the blade is effectively inhibited; meanwhile, the pressure difference between the pressure surface and the suction surface increases. These characteristics greatly improve the performance of wind turbine and increase its torque by more than 30%. Moreover, when the flow control effect cannot be reached, the blade torque is only reduced by approximately 2%.

Prediction of the near wall flow behaviours of separation and transition for NREL phase VI wind turbine blade

ABSTRACT This study demonstrates the separation and transition flow behaviour around a 3-D wind turbine blade by analysing blending functions, intermittency, and transition onset Reynolds number in SST Gamma Theta model. The National Renewable Energy Laboratory Phase VI rotor was modelled for the analysis. The simulations were executed by using the ANSYS-CFX solver. Extensive comparisons were performed to demonstrate the accuracy of this numerical model for sectional pressure distribution, tangent force, normal force, thrust, and torque. Good agreement was observed in all wind speed cases. The discrepancies in pre-stall region were negligible, and those in the post-stall region were acceptable. Thus, the capability and accuracy of the SST Gamma Theta model in predicting separated and transitional flow effects were verified.

Airfoil Shape Optimization of a Horizontal Axis Wind Turbine Blade using a Discrete Adjoint Solver

In this study, airfoil shape optimization of a wind turbine blade is performed using the ANSYS Fluent Adjoint Solver. The aim of this optimization process is to increase the wind turbine output power, and the objective function is to maximize the airfoil lift to drag ratio (Cl/CD ). This study is applied to the NREL phase VI wind turbine, therefore, the S809 airfoil is used as a reference profile. First, for the validation of the applied numerical model, steady-state simulations are carried out for the S809 airfoil at various angles of attack. Then, the optimization is performed with the airfoil set at a fixed angle of attack, , considering three Reynolds numbers, Re =3 105,4.8 105 and 106. Next, computations are performed for the fluid flow around the optimized airfoils at angles of attack AOA= 6.1° ranging from 0° to 20°. The results show that (i) the lift to drag ratios of the optimized airfoils are significantly improved compared to the baseline S809 airfoil, (ii) this improvement is sensitive to the Reynolds number, and (iii) the Cl/CD ratios are also improved for another angle of attack values. Thereafter, the optimized airfoils are used for the design of the NREL Phase VI blade and the aerodynamic performances of this new wind turbine are assessed using the open-source code QBlade. These latter results indicate that when the blades are designed with the optimized airfoils, the wind turbine aerodynamic performances increase significantly. Indeed, at a wind speed of 10 m/s, the power output of the wind turbine is improved by about 38% compared to that of the original turbine.

Passive flow-field control using dimples for performance enhancement of horizontal axis wind turbine

This paper investigates the effectiveness of dimples on the aerodynamic performance of NREL Phase VI wind turbine. Computational fluid dynamics (CFD) was conducted to simulate the turbulent flow and all the forces acting on the rotor. k-ω shear-stress transport (SST) turbulence model was selected to complete the governing equations and multi-reference frame was used as the computational domain. The computational results were compared with the experimental data and previous studies to ensure its reliability. The effect of different dimple configurations, placed at the suction side of the rotor, on the aerodynamic performance of the rotor blade was investigated in terms of the output torque and axial thrust, coefficient of pressure, and the flow field around the blade cross section in the spanwise directions. The results revealed that, dimpled-surface blade could generate up to 8.41% higher output torque compared to the original blade. The results showed no significant deviation in the axial thrust with the addition of the dimples. The modified surface blade with dimples was proven to enhance the operating performance of a wind turbine.

A review of Stall Delay Models and their Application on Hybrid Methods

This paper is a review on the stall delay phenomenon that Horizontal Axis Wind Turbines (HAWT) encounter under typical flow conditions and its numerical modelling. Aerodynamic performance predictions of HAWT have been often carried out through Computational Fluid Dynamics method with the combination of the concept of actuator disk i.e. hybrid method. For this purpose, the hybrid method is presented in details together with the numerical modelling of such stall delay phenomenon. Despite modern wind turbines are equipped with sophisticated control systems for avoiding stall, nevertheless, stall is still inevitable in the near root region of the rotor blade. This paper focuses on recent research development materials which have been undertaken on the stall delay phenomenon where the engineering models (stall delay models) of the literature being presented and criticized based on the predictions obtained from the NREL Phase VI wind turbine experiments.

Wake modeling and simulation of an experimental wind turbine using large eddy simulation coupled with immersed boundary method alongside a dynamic adaptive mesh refinement

Accurate numerical models of the flow around wind turbines is highly relevant for optimizing the energy efficiency of wind farms. The main goal of this work is to apply large eddy simulation (LES) along with an immersed boundary (IB) method to generate spatial and temporal information of the velocity field and forces acting on a fully-resolved NREL S809 airfoil and NREL Phase VI wind turbine. The numerical framework used in the simulations performs LES under a Cartesian block-structured mesh that is dynamically refined via adaptive mesh refinement (AMR) to increase accuracy and reduce computational costs. The mesh refinement criteria is based on Lagrangian points and vorticity. Solid surfaces of the wind turbine are captured using the Lagrangian formulation of the IB method. The simulations are based on the NREL Phase VI wind turbine, where blade analysis of lift and drag coefficients were performed, followed by time-averaged streamwise velocity and vorticity evaluations. For different angles of attack, the wake centerline velocity analysis demonstrates high energy extraction in the near wake of the wind turbine blade. In terms of validation, the drag coefficient of the NREL S809 airfoil achieves better agreement with the experimental data than the lift coefficient. Validation from the NREL Phase VI shows that the power performance difference between the simulation and experiment is lower than 6%. Wake analysis of the wind turbine scenario are based on downstream profiles of the time-averaged streamwise velocity. The numerical simulation shows a higher loss of kinetic energy in the near wake region, mainly in the centerline, compared to benchmark data, but achieves very similar results to literature in the far-wake region.

Arbitrary Hybrid Turbulence Modeling Approach for High-Fidelity NREL Phase VI Wind Turbine CFD Simulation

Today, growth in renewable energy is increasing, and wind energy is one of the key renewable energy sources which is helping to reduce carbon emissions and build a more sustainable world. Developed countries and worldwide organizations are investing in technology and industrial application development. However, extensive experiments using wind turbines are expensive, and numerical simulations are a cheaper alternative for advanced analysis of wind turbines. The aerodynamic properties of wind turbines can be analyzed and optimized using CFD tools. Currently, there is a general lack of available high-fidelity analysis for the wind turbine design community. This study aims to fill this urgent gap. In this paper, an arbitrary hybrid turbulence model (AHTM) was implemented in the open-source code OpenFOAM and compared with the traditional URANS model using the NREL Phase VI wind turbine as a benchmark case. It was found that the AHTM model gives more accurate results than the traditional URANS model. Furthermore, the results of the VLES and URANS models can be improved by improving the mesh quality for usage of higher-order schemes and taking into consideration aeroelastic properties of the wind turbine, which will pave the way for high-fidelity concurrent multidisciplinary design optimization of wind turbines.

CFD Validation and Aerodynamic Behaviour of NREL Phase VI Wind Turbine

In the present study, the 3D flow around the rotating wind turbine whose blade’s geometry is tapered and twisted is observed by using Computational Fluid Dynamics (CFD) as a numerical simulation tool. The CFD simulation of the wind turbines is essential for their efficient use and optimization of the solutions. This paper shows the accuracy of numerical simulation of Reynolds Averaged Navier Stokes equations (RANS equations) along with the Shear Stress transport k-ω turbulence model and validation with the experimental data by the National Renewable Energy Laboratory. All the simulations in this paper are performed on the sequence S of the test configuration of the experiment conducted at the NASA Ames Wind tunnel facility with the blades rotating at constant RPM and varying inlet wind speeds. The results of this study depict a close agreement with the experimental data. The torque predicted by this method is well in line with the experimental values, and it is also able to predict the stalling regions of the wind turbine. This study captures the pre-stall, stall & deep-stall regions and also the 3-dimensional flow around the wind turbine. The flow separation starts occurring on the wind turbine when the inlet speed is greater than 10 m/s, and it is observed that the turbine goes into the deeps stall region when the wind speed is 18m/s.

High-Fidelity 2-Way FSI Simulation of a Wind Turbine Using Fully Structured Multiblock Meshes in OpenFoam for Accurate Aero-Elastic Analysis

With increased interest in renewable energy, the power capacity of wind turbines is constantly increasing, which leads to increased rotor sizes. With ever larger rotor diameters, the complex and non-linear fluid-structure interaction (FSI) effects on wind turbine aerodynamic performances become significant, which can be fully studied using hi-fidelity 2-way FSI simulation. In this study, a two-way FSI model is developed and implemented in Openfoam to investigate the FSI effects on the NREL Phase VI wind turbine. The fully structured multiblock (MB) mesh method is used for the fluid and solid domains to achieve good accuracy. A coupling method based on the ALE is developed to ensure rotation and deformation can happen simultaneously and smoothly. The simulation results show that hi-fidelity CFD (Computational Fluid Dynamics) and CSD (Computational Structural Dynamics) -based 2-way FSI simulation provides high accurate results for wind turbine simulation and multi-disciplinary design optimization (MDO).

CFD simulations of aerodynamic characteristics for the three-blade NREL Phase VI wind turbine model

In order to study the impact of the wind speed and turbulence model on the numerical simulation of the aerodynamic characteristics for the wind turbine, SST k–ω and transition SST turbulence models were used to numerically simulate the aerodynamic characteristics at 7 m/s, 10 m/s and 20 m/s inlet wind speed, and the numerical results were compared with the experimental results. The results show that as the low inlet wind speed, no flow separation occurs over most of the blade surface, and SST k–ω and transition SST turbulence models can accurately predict the aerodynamic characteristics of the blades. As the low inlet wind speed, the flow separation mainly occurs around the root and the middle of blade, and numerical results at the leading edge by SST k-ω turbulence model and near the trailing edge by transition SST turbulence model match the experimental results well. When most of the flow through the blade surface is completely separated, the numerical simulation results by both SST k–ω and transition SST turbulence models have certain differences with experiment results, and the deviations are mainly concentrated on the suction surface and decrease gradually from the blade root to the tip.

Optimization of NREL phase VI wind turbine by introducing blade sweep, using CFD integrated with genetic algorithms

Optimization of NREL phase VI wind turbine by introducing blade sweep, using CFD integrated with genetic algorithms

Numerical Investigation of the Effect of Winglets on Wind Turbine Blades

Numerical investigation of the effect of winglets on NREL Phase VI wind turbine blade is performed. In this research, two different winglet configurations upstream winglet and downstream winglet are compared to see which configuration has the benefit to improve the blade performance. The thickness of winglet tip with the blade shape varied from 100% to 85% and 70% of tip blade thickness to see the effect on blade performance. Moving reference frame method was chosen to perform the blade rotating motion. Computational results were compared with experimental data and it was found that upstream winglet able to increase torque production compared to normal blade up to 1.6%. While downstream winglet decreases. Reducing winglet thickness tends to increase the torque.

Evaluation of three potential machine learning algorithms for predicting the velocity and turbulence intensity of a wind turbine wake

In this paper, three machine learning (ML) algorithms, Support Vector Regression (SVR), Artificial Neural Networks (ANN), and Extreme Gradient Boosting (XGBoost), are validated to estimate the velocity and turbulence intensity of a wind turbine's wake at distinct downstream distances. To this end, a series of high-fidelity numerical simulations for the NREL Phase VI wind turbine is carried out to generate training and test datasets for the three machine learning algorithms. The predicted wake velocity and turbulence intensity from the ML models are also contrasted with significant existing analytical wake models. Machine learning algorithms estimate velocity and turbulence intensity in the wake in a way commensurate to the Computational Fluid Dynamics (CFD) simulations while running at a similar pace as low-fidelity wake models. The results demonstrate that machine learning-based algorithms can predict velocity and turbulence intensity better with higher precision than the traditional analytical wake models.

Influence of leading-edge tubercles on the aerodynamic performance of a horizontal-axis wind turbine: A numerical study

Leading-edge tubercles on the humpback whale pectoral fin are known to have aerodynamic benefits, particularly in the post-stall regime. In this research, a horizontal-axis wind turbine blade was modelled with tubercles distributed on its leading edge to mimic the humpback whale pectoral fin. A parametric study of the effect of tubercles on the reference NREL Phase VI wind turbine was conducted via computational fluid dynamics. Three parameters—amplitude, wavelength, and tubercle location along the blade span—were varied. The results showed that tubercles have negative effects on the turbine performance at wind speeds (V∞) ≤ 7 m/s. However, when tubercles are placed over 60% of the blade span, the backflow area can be eliminated at V∞ = 10 m/s. It is found that the vortices in the stable-flow zone over the suction surface can be reduced when tubercles of a relatively small amplitude-wavelength ratio are employed, thereby maintaining turbine performance. Compared with the reference blade, tubercles provided benefits at higher wind speeds. The generated vortices due to the presence of tubercles, leading to both blockage effects and stall delay. The results revealed that the pressure on the suction surface of the tubercled blade decreases, thereby increasing lift and enhancing the turbine performance.

Numerical Study of a Horizontal Wind Turbine under Yaw Conditions

Over recent years, considerable attention has been devoted to the optimization of energy production in wind farms, where yaw angles can play a significant role. In order to quantify and maximize such potential power, the simulation of wakes is vital. In the present study, an actuator line model code was implemented in the OpenFOAM flow solver. A tip treatment was applied to involve the tip effect induced by the pressure equalization from the suction and pressure sides. The Leishman–Beddoes dynamic stall (LB-DS) model modified by Sheng et al. was employed to consider the dynamic stall phenomenon. The developed ALM-CFD solver was validated for the NREL Phase VI wind turbine reference case. The solver was then used in simulating the yawed wind turbine, and power variation was compared with UBEM and CFD. Overall, according to the obtained data, the coupled solver compared well with CFD. There was an improvement in terms of prediction of the phase delay that is due to the dynamic stall. However, there was still negligible overestimation in deep stall conditions. Based on the obtained results, it is suggested that the reduction of power output follows a cosine to the power of X function of the yaw angle. In terms of visualizing wake, the results demonstrated that the current ALM code was satisfying enough to simulate skewed wake and vortices trajectory. The effect of advancing and retreating blade was captured. It was found that yaw led to the concentration of the induced velocity downstream, resulting in a lower velocity deficit on a broader area, which is essential for wind farm optimization.