scholarly journals Aerodynamically Interacting Vertical-Axis Wind Turbines: Performance Enhancement and Three-Dimensional Flow

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2724 ◽  
Author(s):  
Ian D. Brownstein ◽  
Nathaniel J. Wei ◽  
John O. Dabiri
Keyword(s):  
Wind Direction ◽  
Wind Farm ◽  
Bluff Body ◽  
Performance Enhancement ◽  
Three Dimensional ◽  
Wind Farms ◽  
Vertical Axis ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Turbine Performance

This study examined three-dimensional, volumetric mean velocity fields and corresponding performance measurements for an isolated vertical-axis wind turbine (VAWT) and for co- and counter-rotating pairs of VAWTs with varying incident wind direction and turbine spacings. The purpose was to identify turbine configurations and flow mechanisms that can improve the power densities of VAWT arrays in wind farms. All experiments were conducted at a Reynolds number of R e D = 7.3 × 10 4 . In the paired arrays, performance enhancement was observed for both the upstream and downstream turbines. Increases in downstream turbine performance correlate with bluff–body accelerations around the upstream turbine, which increase the incident freestream velocity on the downstream turbine in certain positions. Decreases in downstream turbine performance are determined by its position in the upstream turbine’s wake. Changes in upstream turbine performance are related to variations in the surrounding flow field due to the presence of the downstream rotor. For the most robust array configuration studied, an average 14% increase in array performance over approximately a 50° range of wind direction was observed. Additionally, three-dimensional vortex interactions behind pairs of VAWT were observed that can replenish momentum in the wake by advection rather than turbulent diffusion. These effects and their implications for wind-farm design are discussed.

scholarly journals Three-Dimensional Velocity Measurements Around and Downstream of a Rotating Vertical Axis Wind Turbine

2014 ◽  
Author(s):  
Kevin J. Ryan ◽  
Filippo Coletti ◽  
John O. Dabiri ◽  
John K. Eaton
Keyword(s):  
Reynolds Number ◽  
Wind Turbines ◽  
Wind Farm ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Mean Velocity ◽  
Scaled Model ◽  
Recirculation Bubble ◽  
Power Extraction ◽  
Turbulent Reynolds Number

Modern designs for straight-bladed vertical axis wind turbines (VAWTs) feature smaller individual footprints than conventional horizontal axis wind turbines (HAWTs), allowing closer spacing of turbines and potentially greater power extraction for the same wind farm footprint. However, the wakes of up-stream turbines could persist far enough to affect the performance of closely-spaced downstream turbines. In order to optimize the inter-turbine spacing and to investigate the potential for constructive aerodynamic interactions, the complex dynamics of VAWT wakes should be understood. The full three-component mean velocity field around and downstream of a scaled model of a rotating VAWT has been measured by Magnetic Resonance Velocimetry (MRV). The model turbine has an aspect ratio (height/diameter) of 1, and was operated in a water facility at subscale but still turbulent Reynolds number of 11,600 based on the turbine diameter. The main flow features including recirculation bubble sizes and strong vortex structures are believed to be representative of flow at full scale Reynolds number. To have kinematic similarity with a power-producing turbine, the model turbine was externally driven. Measurements were taken with the turbine stationary and while driven at tip speed ratios (TSRs) of 1.25 and 2.5, realistic values for VAWTs in operation. The MRV measurement produced three-dimensional velocity data with a resolution of 1/50 of the turbine diameter in all three directions. The flow is shown to be highly three dimensional and asymmetric for the entirety of the investigated region (up to 7 diameters downstream of the turbine). The higher TSR produced greater velocity defect and asymmetry in the near wake behind the turbine, but also showed faster wake recovery than the slower TSR and stationary cases. Wake recovery is affected by a counter-rotating vortex pair generated at the upwind-turning side of the turbine, which mixes faster fluid from the freestream in with the wake. The strength of vortices is shown to increase with TSR.

Performance enhancement of Savonius wind turbine by blade shape and twisted angle modifications

2021 ◽  
pp. 095765092098794
Author(s):  
Ahmed M Nagib Elmekawy ◽  
Hassan A Hassan Saeed ◽  
Sadek Z Kassab
Keyword(s):  
Wind Turbine ◽  
Performance Enhancement ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Cfd Simulations ◽  
Sliding Mesh ◽  
Blade Shape ◽  
Rotor Shape ◽  
Twisting Angle

Three-dimensional CFD simulations are carried out to study the increase of power generated from Savonius vertical axis wind turbines by modifying the blade shape and blade angel of twist. Twisting angle of the classical blade are varied and several proposed novel blade shapes are introduced to enhance the performance of the wind turbine. CFD simulations have been performed using sliding mesh technique of ANSYS software. Four turbulence models; realizable k -[Formula: see text], standard k - [Formula: see text], SST transition and SST k -[Formula: see text] are utilized in the simulations. The blade twisting angle has been modified for the proposed dimensions and wind speed. The introduced novel blade increased the power generated compared to the classical shapes. The two proposed novel blades achieved better power coefficients. One of the proposed models achieved an increase of 31% and the other one achieved 32.2% when compared to the classical rotor shape. The optimum twist angel for the two proposed models achieved 5.66% and 5.69% when compared with zero angle of twist.

Effect of wind turbine nacelle on turbine wake dynamics in large wind farms

2019 ◽  
Vol 869 ◽  
pp. 1-26 ◽  
Author(s):  
Daniel Foti ◽  
Xiaolei Yang ◽  
Lian Shen ◽  
Fotis Sotiropoulos
Keyword(s):  
Wind Turbine ◽  
Coherent Structures ◽  
Large Scale ◽  
Wind Farm ◽  
Wind Farms ◽  
Practical Significance ◽  
Mean Velocity ◽  
Velocity Deficit ◽  
Farm Scale ◽  
Turbine Wake

Wake meandering, a phenomenon of large-scale lateral oscillation of the wake, has significant effects on the velocity deficit and turbulence intensities in wind turbine wakes. Previous studies of a single turbine (Kang et al., J. Fluid. Mech., vol. 774, 2014, pp. 374–403; Foti et al., Phys. Rev. Fluids, vol. 1 (4), 2016, 044407) have shown that the turbine nacelle induces large-scale coherent structures in the near field that can have a significant effect on wake meandering. However, whether nacelle-induced coherent structures at the turbine scale impact the emergent turbine wake dynamics at the wind farm scale is still an open question of both fundamental and practical significance. We take on this question by carrying out large-eddy simulation of atmospheric turbulent flow over the Horns Rev wind farm using actuator surface parameterisations of the turbines without and with the turbine nacelle taken into account. While the computed mean turbine power output and the mean velocity field away from the nacelle wake are similar for both cases, considerable differences are found in the turbine power fluctuations and turbulence intensities. Furthermore, wake meandering amplitude and area defined by wake meanders, which indicates the turbine wake unsteadiness, are larger for the simulations with the turbine nacelle. The wake influenced area computed from the velocity deficit profiles, which describes the spanwise extent of the turbine wakes, and the spanwise growth rate, on the other hand, are smaller for some rows in the simulation with the nacelle model. Our work shows that incorporating the nacelle model in wind farm scale simulations is critical for accurate predictions of quantities that affect the wind farm levelised cost of energy, such as the dynamics of wake meandering and the dynamic loads on downwind turbines.

Modeling of Flow Acceleration Around Wind Farms

2007 ◽  
Author(s):  
Patrick Moriarty ◽  
Tetsuya Kogaki
Keyword(s):  
Wind Farm ◽  
Computational Models ◽  
Three Dimensional ◽  
Wind Farms ◽  
Navier Stokes ◽  
Local Wind ◽  
Flow Acceleration ◽  
Wind Speeds ◽  
Optimum Spacing ◽  
Future Work

Recent measurements from operating wind farms demonstrate that the layout of the farm and interactions between turbine wakes strongly affects the overall efficiency of the wind farm. In some wind farms arranged in rectangular layouts, winds coming from the direction of the rectangular corner create a potential acceleration around the wind farm. This acceleration inherently leads to stronger local wind speeds at wind turbines downstream of the corner turbine, thereby increasing the power output of the downstream turbines. In this study, computational models are developed to predict this complex behavior seen in wind farms. The model used to examine these effects is a fully three-dimensional unsteady incompressible Navier-Stokes code, with the turbulence model turned off. Preliminary results show an optimum spacing configuration is possible. However, the results have yet to be verified at higher Reynolds number, which will be the effort of future work. Ultimately, these tools may lead to more optimal wind farm layouts.

scholarly journals Effects of Jet Induced by String-type Plasma Actuator on Flow Around Three-Dimensional Bluff Body and Drag Force

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 872 ◽  
Author(s):  
Takatoshi Matsubara ◽  
Yoshiki Shima ◽  
Hikaru Aono ◽  
Hitoshi Ishikawa ◽  
Takehiko Segawa
Keyword(s):  
Flow Control ◽  
Bluff Body ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Plasma Actuator ◽  
Recirculation Region ◽  
Back Surface ◽  
Burst Frequency ◽  
Freestream Velocity ◽  
String Type

An experimental investigation of active flow control on a three-dimensional (3D) curved surface bluff body was conducted by using a string-type plasma actuator. The 3D bluff body model tested in this study was composed of a quarter sphere and a half cylinder, and the Reynolds number based on the diameter of half cylinder was set at 1.3 × 104. The modulation drive was adopted for flow control, and the control effects of variations in dimensionless burst frequency (fm+) normalized by the width of the model and freestream velocity were studied. Velocity distributions analyzed by particle image velocimetry showed that the recirculation region behind the model shrank due to the flow control. The static pressure distributions on the back surface of the model tended to decrease under any fm+ set in this study, especially in the ranges of 0.40 ≤ fm+ ≤ 0.64. The drag coefficient reached its maximum value under the similar ranges of fm+. Although the aerodynamic wake sharpening was observed due to the flow control, the entrainment of separated flow into the back surface of the model was enhanced. This scenario of wake manipulation was considered to be responsible for increasing drag acting on the model.

scholarly journals Flow Kinematics in Variable-Height Rotating Cylinder Arrays

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Anna E. Craig ◽  
John O. Dabiri ◽  
Jeffrey R. Koseff
Keyword(s):  
Power Output ◽  
Rotation Rate ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Streamwise Velocity ◽  
Vertical Flow ◽  
Mean Flow ◽  
Freestream Velocity ◽  
Cylinder Arrays ◽  
The Mean

Experimental data are presented for large arrays of rotating, variable-height cylinders in order to study the dependence of the three-dimensional mean flows on the height heterogeneity of the array. Elements in the examined arrays were spatially arranged in the same staggered paired configuration, and the heights of each element pair varied up to ±37.5% from the mean height (kept constant across all arrays), such that the arrays were vertically structured. Four vertical structuring configurations were examined at a nominal Reynolds number (based on freestream velocity and cylinder diameter) of 600 and nominal tip-speed ratios of 0, 2, and 4. It was found that the vertical structuring of the array could significantly alter the mean flow patterns. Most notably, a net vertical flow into the array from above was observed, which was augmented by the arrays' vertical structuring, showing a 75% increase from the lowest to highest vertical flows (as evaluated at the maximum element height, at a single rotation rate). This vertical flow into the arrays is of particular interest as it represents an additional mechanism by which high streamwise momentum can be transported from above the array down into the array. An evaluation of the streamwise momentum resource within the array indicates up to a 56% increase in the incoming streamwise velocity to the elements (from the lowest to highest ranking arrays, at a single rotation rate). These arrays of rotating cylinders may provide insight into the flow kinematics of arrays of vertical axis wind turbines (VAWTs). In a physical VAWT array, an increase in incoming streamwise flow velocity to a turbine corresponds to a (cubic) increase in the power output of the turbine. Thus, these results suggest a promising approach to increasing the power output of a VAWT array.

scholarly journals Theory and Verification of a new 3D RANS Wake Model

2020 ◽  
Author(s):  
Philip Bradstock ◽  
Wolfgang Schlez
Keyword(s):  
Wind Farm ◽  
Three Dimensional ◽  
Wind Farms ◽  
Offshore Wind ◽  
Offshore Wind Farms ◽  
Ambient Flow ◽  
Turbulence Decay ◽  
Local Shear ◽  
Time Lagged ◽  
Wake Model

Abstract. This paper details the background to the WakeBlaster model: a purpose built, parabolic three-dimensional RANS solver, developed by ProPlanEn. WakeBlaster is a field model, rather than a single turbine model; it therefore eliminates the need for an empirical wake superposition model. It belongs to a class of very fast (a few core seconds, per flow case) mid-fidelity models, which are designed for industrial application in wind farm design, operation and control. The domain is a three-dimensional structured grid, with approximately 80 nodes covering the rotor disk, by default. WakeBlaster uses eddy viscosity turbulence closure, which is parameterized by the local shear, time-lagged turbulence development, and stability corrections for ambient shear and turbulence decay. The model prescribes a profile at the end of the near-wake, and the spatial variation of ambient flow, by using output from an external flow model. The WakeBlaster model is verified, calibrated and validated using a large volume of data from multiple onshore and offshore wind farms. This paper presents example simulations for one offshore wind farm.

scholarly journals Investigation of the dissipation in the wake of a wind turbine array

2021 ◽  
Author(s):  
Ingrid Neunaber ◽  
Joachim Peinke ◽  
Martin Obligado
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Bluff Body ◽  
Wind Farms ◽  
Energy Transition ◽  
Mean Velocity ◽  
Maintenance Time ◽  
Bluff Body Wake ◽  
Turbine Wake ◽  
Wind Turbine Wake

Abstract. Within the energy transition, more and more wind turbines are clustered in big wind farms, often offshore. Therefore, an optimal positioning of the wind turbines is crucial to optimize both the annual power production and the maintenance time. Good knowledge of the wind turbine wake and the turbulence within is thus important. However, although wind turbine wakes have been subject to various studies, they are still not fully understood. One possibility to improve the comprehension is to look into the modeling of bluff body wakes. These wakes have been the subject of intensive study for decades, and by means of the scaling behavior of the centerline mean velocity deficit, the nature of the turbulence inside a wake can be classified. In this paper, we introduce the models for equilibrium and non-equilibrium turbulence from classical wake theory as introduced by A. Townsend and W. George, and we test whether the requirements are fulfilled in the wake of a wind turbine. Finally, we apply the theory to characterize the wind turbine wake, and we compare the results to the Jensen and the Bastankhah-Porté-Agel model. We find that the insight into the classical bluff body wake can be used to further improve the wind turbine wake models. Particularly, the classical bluff body wake models perform better than the wind turbine wake models due to the presence of a virtual origin in the scalings, and we demonstrate the possibility of improving the wind turbine wake models by implementing this parameter. We also see how the dissipation changes across the wake which is important to model wakes within wind farms correctly.

scholarly journals Research on the Power Capture and Wake Characteristics of a Wind Turbine Based on a Modified Actuator Line Model

Energies ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 282
Author(s):  
Feifei Xue ◽  
Heping Duan ◽  
Chang Xu ◽  
Xingxing Han ◽  
Yanqing Shangguan ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Output Power ◽  
Wind Turbines ◽  
Wind Farm ◽  
Three Dimensional ◽  
Wind Farms ◽  
Line Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Actuator Line Model

On a wind farm, the wake has an important impact on the performance of the wind turbines. For example, the wake of an upstream wind turbine affects the blade load and output power of the downstream wind turbine. In this paper, a modified actuator line model with blade tips, root loss, and an airfoil three-dimensional delayed stall was revised. This full-scale modified actuator line model with blades, nacelles, and towers, was combined with a Large Eddy Simulation, and then applied and validated based on an analysis of wind turbine wakes in wind farms. The modified actuator line model was verified using an experimental wind turbine. Subsequently, numerical simulations were conducted on two NREL 5 MW wind turbines with different staggered spacing to study the effect of the staggered spacing on the characteristics of wind turbines. The results show that the output power of the upstream turbine stabilized at 5.9 MW, and the output power of the downstream turbine increased. When the staggered spacing is R and 1.5R, both the power and thrust of the downstream turbine are severely reduced. However, the length of the peaks was significantly longer, which resulted in a long-term unstable power output. As the staggered spacing increased, the velocity in the central near wake of the downstream turbine also increased, and the recovery speed at the threshold of the wake slowed down. The modified actuator line model described herein can be used for the numerical simulation of wakes in wind farms.

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