Physical Model Study of the Wind Turbine Array Boundary Layer

2014 ◽  
Author(s):  
Kyle Charmanski ◽  
John Turner ◽  
Martin Wosnik
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Hot Wire ◽  
Flow Measurements ◽  
Model Study ◽  
Power Rate ◽  
First Results ◽  
Upstream Part ◽  
Measurement Location

First results from an experimental investigation of the fully developed wind turbine array boundary layer are reported, using arrays of up to 100 model wind turbines with a diameter of 0.25 m. The wind turbine array was simulated by a combination of drag-matched porous disks, used in the upstream part of the array, and by a smaller array of realistically scaled 3-bladed wind turbines just upstream of the measurement location. The model array was placed in the 6.0 m × 2.7 m × 72.0 m test section of the UNH Flow Physics Facility. Power, rate of rotation and rotor thrust were measured for select turbines, and hot-wire anemometry was used for flow measurements. Development of a fully developed wind turbine array boundary layer was noted with increase in array size.

Experimental Investigation on the Wake Characteristics and Aeromechanics of Dual-Rotor Wind Turbines

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Ahmet Ozbay ◽  
Wei Tian ◽  
Hui Hu
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Large Scale ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Neutral Stability ◽  
Flow Measurements ◽  
Wake Characteristics

An experimental study was carried out to investigate the aeromechanics and wake characteristics of dual-rotor wind turbines (DRWTs) in either co-rotating or counter-rotating configuration, in comparison to those of a conventional single-rotor wind turbine (SRWT). The experiments were performed in a large-scale aerodynamic/atmospheric boundary layer (AABL) wind tunnel, available at Iowa State University with the oncoming atmospheric boundary-layer (ABL) airflows under neutral stability conditions. In addition to measuring the power output performance of DRWT and SRWT models, static and dynamic wind loads acting on those turbine models were also investigated. Furthermore, a high-resolution digital particle image velocimetry (PIV) system was used to quantify the flow characteristics in the near wakes of the DRWT and SRWT models. The detailed wake-flow measurements were correlated with the power outputs and wind-load measurement results of the wind-turbine models to elucidate the underlying physics to explore/optimize design of wind turbines for higher power yield and better durability.

An Experimental Investigation on the Wake Characteristics and Aeromechanics of Dual-Rotor Wind Turbines

2015 ◽  
Author(s):  
Ahmet Ozbay ◽  
Wei Tian ◽  
Hui Hu
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Large Scale ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Neutral Stability ◽  
Flow Measurements ◽  
Wake Characteristics

An experimental study was carried out to investigate the aeromechanics and wake characteristics of dual-rotor wind turbines (DRWTs ) in either co-rotating or counter-rotating configuration, in comparison to those of a conventional single-rotor wind turbine (SRWT). The experiments were performed in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel available at Iowa State University with the oncoming Atmospheric Boundary Layer (ABL) airflows under neutral stability conditions. In addition to measuring the power output performance of DRWT and SRWT models, static and dynamic wind loads acting on those turbine models were also investigated. Furthermore, a high resolution digital particle image velocimetry (PIV) system was used to quantify the flow characteristics in the near wakes of the DRWT and SRWT models. The detailed wake flow measurements were correlated with the power outputs and wind load measurement results of the wind turbine models to elucidate the underlying physics to explore/optimize design of wind turbines for higher power yield and better durability.

scholarly journals Impacts of the low-level jet's negative wind shear on the wind turbine

2017 ◽  
Vol 2 (2) ◽  
pp. 533-545 ◽  
Author(s):  
Walter Gutierrez ◽  
Arquimedes Ruiz-Columbie ◽  
Murat Tutkun ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Real Life ◽  
Horizontal Wind ◽  
Major Power ◽  
Low Level ◽  
Wind Speed Maximum ◽  
Wind Shears

Abstract. Nocturnal low-level jets (LLJs) are defined as relative maxima in the vertical profile of the horizontal wind speed at the top of the stable boundary layer. Such peaks constitute major power resources for wind turbines. However, a wind speed maximum implies a transition from positive wind shears below the peak to negative ones above. The effect that such a transition has on wind turbines has not been thoroughly studied.This research study employed a methodical approach to the study of negative wind shear's impacts on wind turbines. Up to now, the presence of negative shears inside the turbine's rotor in relation to the presence of positive shears has been largely ignored. A parameter has been proposed to quantify that presence in future studies of LLJ–wind-turbine interactions. Simulations were performed using the NREL aeroelastic simulator FAST code. Rather than using synthetic profiles to generate the wind data, all simulations were based on real data captured at the high frequency of 50 Hz, which allowed us to perform the analysis of a turbine's impacts with real-life, small scales of wind motions.It was found that the presence of negative wind shears at the height of the turbine's rotor appeared to exert a positive impact on reducing the motions of the nacelle and the tower in every direction, with oscillations reaching a minimum when negative shears covered the turbine swept area completely. Only the tower wobbling in the spanwise direction was amplified by the negative shears; however, this occurred at the tower's slower velocities and accelerations. The forces and moments were also reduced by the negative shears. The aforementioned impacts were less beneficial in the rotating parts, such as the blades and the shafts. Finally, the variance in power production was also reduced. These findings can be very important for the next generation of wind turbines as they reach deeper into LLJ's typical heights.The study demonstrated that the presence of negative shears is significant in reducing the loading on wind turbines. A major conclusion of this study is that the wind turbines of the future should probably be designed with the aim of reaching the top of the nightly boundary layer more often and therefore the altitudes where negative shears are more frequent. Doing so will help to reduce the positive shear's associated damage and to capture the significant LLJ energy.

Modeling of Aerodynamically Generated Noise From Wind Turbines

2005 ◽  
Vol 127 (4) ◽  
pp. 517-528 ◽  
Author(s):  
Wei Jun Zhu ◽  
Nicolai Heilskov ◽  
Wen Zhong Shen ◽  
Jens Nørkær Sørensen
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Aerodynamic Noise ◽  
Generation Model ◽  
Two Dimensional ◽  
Noise Emission ◽  
Total Noise ◽  
Element Input ◽  
Blade Element

A semiempirical acoustic generation model based on the work of Brooks, Pope, and Marcolini [NASA Reference Publication 1218 (1989)] has been developed to predict aerodynamic noise from wind turbines. The model consists of dividing the blades of the wind turbine into two-dimensional airfoil sections and predicting the total noise emission as the sum of the contribution from each blade element. Input is the local relative velocities and boundary layer parameters. These quantities are obtained by combining the model with a Blade Element Momentum (BEM) technique to predict local inflow characteristics to the blades. Boundary layer characteristics are determined from two-dimensional computations of airfoils. The model is applied to the Bonus 300 kW wind turbine at a wind speed of 8 m/s. Comparisons of total noise spectra show good agreement with experimental data.

scholarly journals Development and Validation of CFD 2D Models for the Simulation of Micro H-Darrieus Turbines Subjected to High Boundary Layer Instabilities

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5564
Author(s):  
Rosario Lanzafame ◽  
Stefano Mauro ◽  
Michele Messina ◽  
Sebastian Brusca
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Fluid Dynamic ◽  
Vertical Axis ◽  
Operating Conditions ◽  
Time Step ◽  
Vertical Axis Wind Turbines ◽  
2D Model

The simulation of very small vertical axis wind turbines is often a complex task due to the very low Reynolds number effects and the strong unsteadiness related to the rotor operation. Moreover, the high boundary layer instabilities, which affect these turbines, strongly limits their efficiency compared to micro horizontal axis wind turbines. However, as the scientific interest toward micro wind turbine power generation is growing for powering small stand-alone devices, Vertical Axis Wind Turbines (VAWTs)might be very suitable for this kind of application as well. Furthermore, micro wind turbines are widely used for wind tunnel testing, as the wind tunnel dimensions are usually quite limited. In order to obtain a better comprehension of the fluid dynamics of such micro rotors, in the present paper the authors demonstrate how to develop an accurate CFD 2D model of a micro H-Darrieus wind turbine, inherently characterized by highly unstable operating conditions. The rotor was tested in the subsonic wind tunnel, owned by the University of Catania, in order to obtain the experimental validation of the numerical model. The modeling methodology was developed by means of an accurate grid and time step sensitivity study and by comparing different approaches for the turbulence closure. The hybrid LES/RANS Delayed Detached Eddy Simulation, coupled to a transition model, demonstrated superior accuracy compared to the most advanced unsteady RANS models. Therefore, the CFD 2D model developed in this work allowed for a thorough insight into the unstable fluid dynamic operating conditions of micro VAWTs, leading the way for the performance improvement of such rotors.

Modeling of the atmospheric boundary layer under stability stratification for wind turbine wake production

2019 ◽  
pp. 0309524X1988092
Author(s):  
Mohamed Marouan Ichenial ◽  
Abdellah El-Hajjaji ◽  
Abdellatif Khamlichi
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Large Scale ◽  
Wind Farm ◽  
Layer Structure ◽  
Atmospheric Stability ◽  
Weather Conditions ◽  
Boundary Layer Structure

The assessment of climatological site conditions, airflow characteristics, and the turbulence affecting wind turbines is an important phase in developing wake engineering models. A method of modeling atmospheric boundary layer structure under atmospheric stability effects is crucial for accurate evaluation of the spatial scale of modern wind turbines, but by themselves, they are incapable to account for the varying large-scale weather conditions. As a result, combining lower atmospheric models with mesoscale models is required. In order to realize a reasonable approximation of initial atmospheric inflow condition used for wake identification behind an NREL 5-MW wind turbine, different vertical wind profile models on equilibrium conditions are tested and evaluated in this article. Wind farm simulator solvers require massive computing resources and forcing mechanisms tendencies inputs from weather forecast models. A three-dimensional Flow Redirection and Induction in Steady-state engineering model was developed for simulating and optimizing the wake losses of different rows of wind turbines under different stability stratifications. The obtained results were compared to high-fidelity simulation data generated by the famous Simulator for Wind Farm Applications. This work showed that a significant improvement related to atmospheric boundary layer structure can be made to develop accurate engineering wake models in order to reduce wake losses.

scholarly journals On the Wind Turbine Wake and Forest Terrain Interaction

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7204
Author(s):  
Shyuan Cheng ◽  
Mahmoud Elgendi ◽  
Fanghan Lu ◽  
Leonardo P. Chamorro
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Boundary Layers ◽  
Wind Turbines ◽  
Quadrant Analysis ◽  
Optimized Design ◽  
Incoming Flow ◽  
High Background ◽  
Forest Density ◽  
Turbine Wake

Future wind power developments may be located in complex topographic and harsh environments; forests are one type of complex terrain that offers untapped potential for wind energy. A detailed analysis of the unsteady interaction between wind turbines and the distinct boundary layers from those terrains is necessary to ensure optimized design, operation, and life span of wind turbines and wind farms. Here, laboratory experiments were carried to explore the interaction between the wake of a horizontal-axis model wind turbine and the boundary layer flow over forest-like canopies and the modulation of forest density in the turbulent exchange. The case of the turbine in a canonical boundary layer is included for selected comparison. The experiments were performed in a wind tunnel fully covered with tree models of height H/zhub≈0.36, where zhub is the turbine hub height, which were placed in a staggered pattern sharing streamwise and transverse spacing of Δx/dc=1.3 and 2.7, where dc is the mean crown diameter of the trees. Particle image velocimetry is used to characterize the incoming flow and three fields of view in the turbine wake within x/dT∈(2,7) and covering the vertical extent of the wake. The results show a significant modulation of the forest-like canopies on the wake statistics relative to a case without forest canopies. Forest density did not induce dominant effects on the bulk features of the wake; however, a faster flow recovery, particularly in the intermediate wake, occurred with the case with less dense forest. Decomposition of the kinematic shear stress using a hyperbolic hole in the quadrant analysis reveals a substantial effect sufficiently away from the canopy top with sweep-dominated events that differentiate from ejection-dominated observed in canonical boundary layers. The comparatively high background turbulence induced by the forest reduced the modulation of the rotor in the wake; the quadrant fraction distribution in the intermediate wake exhibited similar features of the associated incoming flow.

Uncertainty Analysis in a Scale Model Wind Turbine Array Boundary Layer

2017 ◽  
Author(s):  
John J. Turner ◽  
Martin Wosnik
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Turbulent Boundary Layer ◽  
Uncertainty Analysis ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Test Section ◽  
Scale Model ◽  
Acquisition Time ◽  
Flow Physics

Uncertainty estimates from an experimental investigation of a scale model wind turbine array, conducted with (on the order of) 100 0.25 meter diameter model wind turbines in a high Reynolds number turbulent boundary layer facility, are reported. An expanded uncertainty analysis using the Taylor series method is executed to predict uncertainty for the system of interest in the mean flow. A workable comprise has been found for data acquisition time mitigating changing initial conditions due to exposure to atmospheric conditions and temperature drift. The study was conducted in the University of New Hampshire (UNH) Flow Physics Facility (FPF) which is the worlds largest flow physics quality turbulent boundary layer wind tunnel, with test section dimensions of 6 m wide, 2.7 m tall and 72 m long. Naturally grown turbulent boundary layers with scale ratios of energy-containing to dissipative scales (Karman number) of up to 20,000 can be generated, and are on the order of 1 m thick near the downstream end of the test section. The long fetch of the facility offers unique opportunities to study the downstream evolution of the wake of single wind turbines, and the flow through model wind turbine arrays over long distances. Far downstream within a wind farm it is proposed that the farm reaches a fully developed state where the flow field becomes similar from one row to the next. The goal of this work is to accurately determine the uncertainty associated with open to atmosphere wind tunnel data for use in validation of numerical models regarding the fully developed wind turbine array boundary layer.

Modeling the Wind Turbine Profiles Assuring the Maximum Lift Force With Low-Noise Operation for Variable Wind Velocities

2018 ◽  
Author(s):  
Victorita Radulescu
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Lift Force ◽  
Acoustic Emissions ◽  
Low Noise ◽  
Trailing Edge ◽  
Term Operation ◽  
Wind Velocities

The paper presents a new solution for the wind turbine profile shape modeling based on the concept of the maximum lift force, capable to be produced at different values of the wind velocities. The profile is designed and realized in accordance with the new concept emerged in the last decade, on the operation of the wind turbines with maximum lifting force. The purpose is to provide a low-noise during operation because a negative effect on the medium and long-term operation of the wind turbines (wind farms) is the noise that affects the flight of birds, terrestrial animal life, and especially human communities. Various sources generate independent acoustic emissions on wind profiles, such as the turbulent flow, the interaction of the turbulent boundary layer area of the trailing edge, the flow separation, and the boundary layer separation of vortices formed in the zone of the trailing edge. There is also considered the influence of the apparent wind on the incidence variation of the profile. In order to maintain an optimum angle of attack relative to the wind velocity, a fixed blade inclination must increase its speed to be proportional to the wind. Thus, to maximize the aerodynamic performance, the rotor must spin faster when the wind intensity increases. Measurement of the acoustic signal requires electronic devices that operate on electric signals obtained from the conversion of the pressure variations in voltage or variations in electrical current. The noise caused by the turbulent flow is generated primarily by the sharply pointed leading edge and cannot be diminished. There are presented some numerical results correlated with the measurements made in the field.

scholarly journals Fatigue of polyamide mooring ropes for floating wind turbines

2018 ◽  
Vol 165 ◽  
pp. 10002 ◽  
Author(s):  
Yoan Chevillotte ◽  
Yann Marco ◽  
Peter Davies ◽  
Guilhem Bles ◽  
Maël Arhant
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Offshore Platform ◽  
Fatigue Performance ◽  
Station Keeping ◽  
Suitable Alternative ◽  
First Results ◽  
Heat Build Up

This paper describes a study of the fatigue characterization of polyamide mooring ropes for floating wind turbines. Under some conditions polyester ropes, which are favoured for offshore platform station-keeping, are too stiff for wind turbine moorings, and polyamide may be a suitable alternative. While early studies on fatigue of braided nylon ropes showed very short lifetimes some recent results have indicated that it is possible to significantly enhance lifetime by modifying rope construction and improving fibre coatings [1]. The fatigue results presented here for ropes from a different supplier, confirm this result. In order to develop an accelerated evaluation of the fatigue performance, heat build-up tests have been performed, and promising first results are shown. Finally, the influence of coating is examined by microscopy and yarn-on-yarn tests, in order to improve understanding of the fatigue mechanisms leading to failure.

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