North American Wind Energy Academy 2015 Symposium

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https://hdl.handle.net/10919/52370

The NAWEA 2015 Symposium, which was held June 9-11, 2015 at Virginia Tech in Blacksburg, VA, included technical sessions, panel discussions, a graduate student symposium, a poster session, engineering software workshops, a business meeting, social events, and a tour of the Virginia Tech Stability Tunnel. The Symposium, the second in a series of technical meetings, examined a broad range of topics required to achieve high wind penetration in the North American power-generation sector. In addition to wind energy system science and technology technical tracks, the symposium featured sessions that provided holistic perspectives, overviews, and approaches necessary to maximize future deployment including:

Research and Development, and Technology, including presentations on Aerodynamics, Aeroacoustics, Controls, Innovative Systems and Concepts, Reliability, Offshore, etc.
Electrical Integration, including presentations on issues of achieving high penetration of variable renewables and on energy storage issues
Atmosphere/Turbine/Wake Interactions, including farm/plant interactions and array effects
Atmospheric Science of Wind Characterization, and Forecasting
Public Policy Issues, including presentations, and a panel discussion of issues/problems and how technology can provide solutions, economics of wind
Environmental and Siting Issues, including presentations, and a panel discussion of issues/problems and how technology can provide solutions
Workforce Development and Education, including presentations, and a panel discussion from the Education Committee

- http://www.cpe.vt.edu/nawea/index.html, retrieved 2015-05-13

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Now showing 1 - 20 of 82

Academic Qualification in Onshore and Offshore Wind Energy within the Framework of the European Academy of Wind Energy and the European Wind Energy Master Program - Examples and Experiences in Germany and Europe
Kaern, Moses (Virginia Tech, 2015-06-10)
The development of research and education in wind energy in Europe varies greatly between the member states. Building on these national achievements the European Academy of Wind Energy (EAWE) is integrating and connecting the activities of the highest level academic and research institutes in Europe. Leading universities in The Netherlands, Denmark, Germany, and Norway have joined forces to form the elite European Wind Energy Master (EWEM) building on different local programs at the partner universities: Delft University of Technology, Technical University of Denmark, Carl von Ossietzky University Oldenburg, Norwegian University of Science and Technology. While academic education on master and PhD levels is strongly based on international cooperation and consortia, the barriers in professional and continuing education to cooperate internationally are higher. The presentation will explain the concepts of the European Wind Energy Master and the continuing study programs Wind Energy Technology and Management and Offshore Wind Energy. Possibilities for cooperation will be discussed.
Aerodynamic Effects of Painted Surface Roughness on Wind Turbine Blade Performance
Joseph, Liselle AnnMarie; Borgoltz, Aurelien; Kuester, Matthew; Devenport, William J.; Fenouil, Julien (Virginia Tech, 2015-06-09)
This paper briefly examines the aerodynamic effects of typical wind turbine blade roughness by investigating an appropriate scaling criteria which best relates the roughness configuration to the resulting changes in aerodynamic forces and transition. The wind tunnel test results of two wind turbine blade sections tested with three different roughness samples are presented. The two models, consisting of a 457mm-chord and 800mm-chord airfoils using the DU96-W-180 profile, were tested in the Virginia Tech Stability Wind Tunnel at free-stream Reynolds number based on the chord between 1.5 and 3M. Preliminary analysis of the lift and drag scaling are presented as well as a sample of the transition results.
Aerodynamic Validation of Wind Turbine Airfoil Models in the Virginia Tech Stability Wind Tunnel
Kuester, Matthew; Brown, Kenneth; Meyers, Timothy; Intaratep, Nanyaporn; Borgoltz, Aurelien; Devenport, William J. (Virginia Tech, 2015-06-09)
Aerodynamics and Aeroacoustics of Spanwise Wavy Trailing Edge Flatback Airfoils: Design Improvement
Yang, Seung Joon; Baeder, James D. (Virginia Tech, 2015-06)
The spanwise wavy trailing edge design considering its structural benefits was proposed and studied. The three dimensional RANS-LES simulation has been performed to reveal the aerodynamic and aeroacoustic behaviors of the newly proposed wavy trailing edge design.
Analysis of Tower Shadow Effects on the UAE Rotor Blades
Noyes, Carlos; Loth, Eric; Qin, Chao (Virginia Tech, 2015-06)
A leading obstacle hindering the development of wind turbines to extreme scale is the structural integrity of the blades. Downwind rotors have been shown to give structural advantages for larger systems. However, there is an added aerodynamic complication from the tower shadow. This paper presents and analyzes a previously unpublished subset of data collected by NREL during an extensive wind tunnel campaign for Unsteady Aerodynamic Experiment Phase VI (UAE Phase VI). The experimental data includes relative flow fields, aerodynamic blade forces, and root blade flapwise bending moments, from upwind turbines, downwind turbines and downwind turbines with the use of an aerodynamic tower fairing. It is shown that the tower shadow can have a severe and negative effect on these variables, leading to higher bending stresses. The use of a tower fairing can greatly reduce these detrimental effects. To better interpret this data, predictions using an aeroelastic wind turbine code, FAST, was used to model the experimental conditions. The differences between the experimental data and the computational predictions are attributed to unsteady effects of the wake. This suggest that wake modeling for downwind turbines may require modifications to capture physically realistic tower shadow effects.
Analysis of Turbine Wake Characteristics using Proper Orthogonal Decomposition and Triple Decomposition Methods
Premaratne, Pavithra; Tian, Wei; Hu, Hui (Virginia Tech, 2015-06)
In the present study, we report the progress made in our efforts to examine the wake flow characteristics behind a commonly-used three-bladed horizontal-axis wind turbine. A series of experiments were performed in a large-scale wind tunnel with a scaled wind turbine model placed in a typical Atmospheric Boundary Layer (ABL) wind under neutral stability conditions. In addition to measuring dynamic wind loads acting on the model turbine by using a force- moment sensor, a high-resolution digital particle image velocimetry (PIV) system was used to achieve detailed flow field measurements to quantify the characteristics of the turbulent vortex flow behind the turbine model. Besides conducting “free-run” PIV measurements to determine the ensemble-averaged statistics of the flow quantities such as mean velocity, Reynolds stress, and turbulence kinetic energy (TKE) distributions in the wake flow, “phase-locked” PIV measurements were also performed to elucidate further details about evolution of the unsteady wake vortex structures in relation to the position of the rotating turbine blades. The detailed flow field measurements were used to validate the analytical models for the velocity deficit prediction in turbine wakes. Proper Orthogonal Decomposition (POD) method was employed in the present study for the data reduction of the PIV measurement results to identify the high energy modes that dominate the turbulent kinetic energy distributions in the turbine wakes. Triple Decomposition (TD) approach was also used to analyze the phase-locked PIV measurement results to elucidate the underling physics related to the intensive turbulent mixing process in the wake flow, which would promote the vertical transport of kinetic energy to entrain more high-speed airflow from above to re-charge the wake flow behind the wind turbine model.
An Analytical Procedure for Evaluating Aerodynamics of Wind Turbines in Yawed Flow
Rajagopalan, R. Ganesh; Guntupalli, Kanchan; Fischels, Mathew V.; Novak, Luke A. (Virginia Tech, 2015-06)
A new analytical method for evaluating the performance of wind turbines in yawed flow is presented. The method, based on momentum theory, relates the yaw angle to the tip-path-plane orientation of the turbine rotor and the non-dimensional deficit velocity. The analytical calculations are compared with results from Rot3DC, a kernel within the RotCFD software package, an integrated environment for rotors. Rot3DC, a 3-D Navier-Stokes based module, can simulate one or more Horizontal Axis Wind Turbines (HAWT) and uses the concept of momentum sources to compute the turbine performance and flowfield in a self contained manner. Rot3DC simulations are validated against NREL Phase-II experiments. Analytical results for yawed turbines correlate well with Rot3DC and are found to be within 10% error margin for the extreme yaws considered. The developed analytical formulation provides a simple model for quantification of turbine performance in yawed flow and can be used as an input to onboard feedback systems for yaw control.
Analytical Unsteady aerodynamics model of a Horizontal axis wind turbines due to linear change in wind speed
Hammam, Mohamed (Virginia Tech, 2015-06)
Small wind turbines use MPPT (Maximum power point Tracking) algorithm that depends on the performance relation developed using a steady BEM [Blade Element Momentum] code. However, small wind turbines work under harsh unsteady environment that is subjected to large fluctuation in wind and rotor speeds. This will lead to unsteady power generated that differ significantly from the one predicted using steady codes. In this work, a semi-empirical model is developed that correlates an unsteady physical variable, like the unsteady stream line length, to a measurable variable in unsteady operation, like tip speed ratio. This model use the unsteady Euler equation supplied with a measured data of power coefficient and wind speed of a 5 kW wind turbine. The analysis shows that the stream line length shows some correlation with tip speed ratio. Further data analysis is currently underway to investigate this correlation and further results will be reported in the final presentation.
Application of Fast Pressure-Sensitive Paint to an Oscillating Wind Turbine Airfoil
Disotell, Kevin J.; Nikoueeyan, Pourya; Naughton, Jonathan W.; Gregory, James W. (Virginia Tech, 2015-06)
In the unsteady flow environment experienced by wind turbine blades, large excursions in local angle of attack and significant three-dimensional flows arise that complicate the prediction of stall onset and unsteady loading. Accurate predictions of the dynamic loads are critical to the pursuit of lightweight, reliable structures to lower the cost of wind energy (Ref. 1). To this end, diagnostic measurement tools capable of fine spatial resolution and high frequency response are important for better understanding unsteady aerodynamic effects on blade pressure distribution. The sparseness of conventional pressure transducers has historically provided motivation for the development of pressure-sensitive paint (PSP), an optical surface pressure measurement technique with inherently fine spatial resolution. Within the last decade, the bandwidth of certain paint formulations has been significantly increased to resolve unsteady flows; a flat frequency response on the order of several kHz is now readily achievable (Ref. 2). PSP consists of luminescent molecules adhered to the test surface by a thin binder layer, typically on the order of 10 microns. The luminophore responds to the local partial pressure of oxygen, which is directly proportional to absolute air pressure. An illumination source such as a light-emitting diode or expanded laser beam excites the luminophore, and the emitted light intensity captured by a scientific-grade camera is converted to absolute pressure via calibration. Each point on the painted surface thus responds as a molecular-sized transducer, with spatial resolution limited by the camera pixel size. Recent advancements in unsteady PSP data acquisition and processing techniques have been developed for rotating blades to account for errors caused by model movement and deformation in nonuniform illumination fields. The single-shot lifetime technique (Ref. 3) and motion capturing technique (Ref. 4) are two methods which have arisen. Due to its straightforward procedure and commonality of required hardware, the single-shot technique has been used across a range of small test facilities (Ref. 5, 6) and large-scale wind tunnels (Ref. 7). PSP measurements have been historically limited to the compressible flow regime to achieve sufficient signal-to-noise ratio in the data images (Ref. 8, 9). Recent wind tunnel testing with unsteady PSP has been geared toward helicopter applications (Ref. 10, 11), although temperature error due to compressibility effects has been noted. Under isothermal conditions or with an accurate temperature correction available, laser-based excitation and highly reflective paints can enable instantaneous PSP measurements at Mach numbers near M ≈ 0.15, corresponding to dynamic pressures of approximately 1.5 kPa (Ref. 6, 12). Unsteady aerodynamic effects can result in even larger pressure differences, considering that peak suction levels on oscillating airfoils can reach factors of the free stream dynamic pressure (Ref. 13). With the present availability of suitable paints, the above considerations present an opportunity for PSP to be deployed as a measurement tool for resolving the global pressure distribution on wind turbine blades.
Assessing the Structural Impact of Low Level Jets over Wind Turbines
Gutierrez, Walter; Araya, Guillermo; Kiliyanpilakkil, Praju; Basu, Sukanta; Ruiz-Columbie, Arquimedes; Tutkun, Murat; Castillo, Luciano (Virginia Tech, 2015-06)
Low Level Jets (LLJs) are defined as regions of relatively strong winds in the lower part of the atmosphere. They are a common feature over the Great Plains in the United States. It has been reported that 75 % of LLJs in the Great Plains occur at night and with seasonal patterns, affecting significantly the wind energy production. Present results have corroborated some of the LLJ's known characteristics. LLJs develop due to the formation of stable stratification in the lower atmosphere. This paper is focused on the determination of the static/dynamic impact that real LLJs produced in West Texas have over wind turbines. High-frequency (50Hz) observational data from the 200-m tower data (Reese, Texas) have been input as inflow conditions into the NREL FAST code in order to evaluate the structural impacts of LLJ's on a typical wind turbine. Due to the higher levels of wind speed, the potential for power increase proportional to the cube of the velocity. It has been observed that during an LLJ event the level of turbulence intensities and TKE are significantly much lower than those during unstable conditions; as a result, cyclical aerodynamic loads on turbine blades are different. Low-frequency oscillations prevail in stable conditions with formation of LLJ, as opposed to high-frequency oscillations more prevalent in unstable conditions. The turbulent kinetic energy is lower in LLJ but the energy concentrates in particular frequencies that can stress the turbine. From the point of view of the wind turbine loads/stresses, we have detected frequencies that can be correlated with those from the incoming wind.
Benefits of vertically-staggered wind turbines from theoretical analysis and Large-Eddy Simulations
Archer, Cristina L.; Xie, Shengbai; Ghaisas, Niranjan; Meneveau, Charles (Virginia Tech, 2015-06)
Bio-Inspired Trailing Edge Noise Control
Clark, Ian; Alexander, William Nathan; Devenport, William J.; Glegg, Stewart; Jaworski, Justin; Peake, Nigel; Daly, Conor (Virginia Tech, 2015-06)
Trailing edge noise remains a primary limiting factor in the widespread implementation of wind turbines, particularly near populated areas. Noise regulations commonly require acoustic de-rating of existing turbines, leading to reduced output and revenue. This presentation will describe an experimental study aimed at trailing edge noise control inspired by the unique features found on the wings of owls that use acoustic stealth while hunting prey. One of these features is a thin layer of fine hairs which grow from the exposed surfaces of the flight feathers. These hairs have been investigated and found to form a sort of canopy suspended above the surface of the owl's feathers. Previous wall-jet tunnel measurements have shown that high open-area canopies of similar characteristics can reduce surface pressure fluctuations on the underlying surface by as much as 30dB, and significantly attenuate roughness noise generated by that surface. In the present work, treatments designed to replicate the effects of the canopy in a form suitable for application to an airfoil have been designed and tested in the Virginia Tech Stability Wind Tunnel. Over 20 variants of these designs have been tested by performing aeroacoustic wind tunnel measurements on a tripped DU96-W180 airfoil at chord Reynolds numbers up to 3 million. Exact details of the treatments are not given here since they are the subject of a current patent application, but the treatments will be described during the presentation. Variations include treatment thickness, density, length, position relative to the trailing edge and the effectiveness of treating only one side of the trailing edge. The treatments were placed over the center-half span of the airfoil in the trailing edge region. Measurements included far-field acoustic data from a 117-microphone phased array and mean surface pressure data from 80 pressure taps distributed over the airfoil profile. For some conditions a rake of Pitot and static probes was used to measure profiles through the airfoil wakes and infer the drag using a momentum balance approach. Compared to the unmodified airfoil the treatments were found to be quite effective. Acoustic beamform maps and integrated spectra show up to 10dB of broadband attenuation of trailing edge noise in the vicinity of the treatment. The majority of the noise attenuation was observed in the frequency range above 1500Hz, but measurements below this frequency are inconclusive because of the large spot size of the phased array at these frequencies. The treatment remains effective throughout a wide parameter range and is not highly dependent on a particular geometry, but there appears to be strong potential for optimization. Treatments were found to be effective over an angle of attack range that extends over 10 degrees from zero lift. Compared to the unmodified airfoil, no additional noise was measured from the treated airfoil past this 10 degree range. The mean surface pressure data revealed that the presence of the treatment had little impact on the lift characteristics of the airfoil model. Drag rake results showed a small increase in drag proportional to the increase in wetted area resulting from the addition of the treatment to the unmodified airfoil.
CFD Analysis of NACA4415 Airfoil with ƴ – Re₀ Model considering Natural Transition
Islam, Mazhural; Langfeldt, Felix; Juretic, Franjo; Guerrero, Joel; Wood, David H. (Virginia Tech, 2015-06)
Airfoil analysis is essential to wind turbine aerodynamics. In typical operating conditions, airfoils undergo transition from laminar to turbulent flow in the boundary layer in a manner that must be modeled accurately to predict airfoil lift and drag. There are different modes of transition (e.g. natural, by-pass, wake induced, reversed, separated flow) and modeling them is not straight-forward. Over the years, diversified predictions have been developed for the various modes. One of the popular transition models is the local correlation-based ƴ - Re₀ model of Menter et al. (Menter et al., 2004). The model requires data correlations for the transition length and the critical Reynolds numbers.
Characterizing Long-Time Variations in Fully Developed Wind-Turbine Array Boundary-Layers using Proper Orthogonal Decomposition
VerHulst, Claire; Meneveau, Charles (Virginia Tech, 2015-06-08)
Co-location of Wind and Solar Power Plants and Their Integration onto the US Power Grid
Pattison, Chris (Virginia Tech, 2015-06)
A number of research and development groups and several renewable project operators have examined combining wind power production with on-site solar power production. Past research has been devoted to small, off-grid applications only. In the absence of actually building a utility-scale project, short time scale (5 minutes) estimates of combined power production are difficult to simulate due to the lack of hub-height wind data combined with on-site solar insolation data available in similar time scales. This presentation will present hub-height, high-fidelity, wind data from the Texas Tech University's 200-meter meteorological tower combined with a co-located solar pyranometer to estimate short-term (5-minute) power production data. Recent reduced costs associated with solar-PV may make this option more attractive in the future. This analysis addresses fixed-plate, single- and dual-axis PV arrays. This presentation also includes an plant-level and grid-level economic analysis of a wind-only, solar-only, and combined wind-solar power plant. Over the past few years, renewable energy has entered the electrical grid at an exponential rate. To reduce the uncertainties for the grid operator and wind power plants owner/operators, "firm" production has a direct impact on the power purchase agreements (PPA's). Since wind power is traditionally best at night and solar power is only during the day, by combining their synergies, uncertainty is reduced and higher PPA's are possible. This analysis will present economic estimates of the ability of plant operators to secure higher purchase prices for power by raising the "firm" production level and reducing risk.
Combined Offshore Wind, Wave, Storage System Power and Cost Predictions
Kluger, Jocelyn (Virginia Tech, 2015-06-08)
Combining economic and fluid dynamic models to determine optimal spacing in very large wind-farms
Stevens, Richard; Hobbs, Benjamin; Ramos, Andres; Meneveau, Charles (Virginia Tech, 2015-06)
Now that wind-farms are becoming increasingly larger, the economics and physics of wind farms become intrinsically coupled and important when designing large wind farms. It is important to develop wind farm models in which economic considerations can be combined with physical considerations in a transparent and intuitive way. For smaller wind-farms the majority of the turbines can be placed such that physical wake effects are relatively limited and thus physical effects may be less important. However, for large wind farms (e.g. with hundreds or thousands of turbines) it is important to consider the influence of wake effects on the optimal turbine spacing. For the design of wind-farms the industry uses site-specific, detailed optimization calculations for wind-turbine placement based on wake models (1; 2; 3; 4; 5; 6). Such calculations aim to place the turbines such that wake effects are limited with respect to the prevailing incoming wind-directions at the site under consideration. There are also academic studies that use wake models to optimize turbine placement using Monte Carlo simulations (7), genetic algorithms (8), or evolutionary algorithms (9; 10). In this work we will combine economic and fluid dynamic models to determine the main parameters that are important for the design of very large wind-farms.
Comparison of Offshore Wind Turbine Reliability
Christou, Aristos; McCluskey, Patrick; Lu, Yizshou; Delorm, Tatiana (Virginia Tech, 2015-06)
The results of a comparative probabilistic reliability model applied to offshore wind turbine systems is presented. The model calculations are based on surrogate failure rate data from industrial onshore wind turbine technologies, related marine environment technologies and generic databases. Data are adjusted for the offshore marine environment and integrated with functional as well as reliability block diagrams. The developed models are applied to five generic horizontal-axis offshore wind turbine designs. Predicted subsystem failure rates and total system failure rates are reported and critical reliability limiting sub-assemblies are identified.
Computational Modelling of Solidity Effects on Blade Elements with an Airfoil Profile for Wind Turbines
Yan, Haoxuan (Virginia Tech, 2015-06-08)
The aim of this project is to investigate the aerodynamic performances of airfoil, especially NACA 4415, using the method of Computational Fluid Dynamics. The NACA 4415 was modeled and meshed in ICEM and then was simulated by using transition SST (shear stress transport) 4-equation model in ANSYS Fluent 15.0 with different Reynolds number and various angles of attack. Lift, drag, pressure distribution and wall shear stress were highly focused during post-processing. The computational results were compared with Xfoil and experimental data collected by The Ohio State University (OSU) in 1996. User Defined Functions (UDF) were also tested during the calculations in order to find the most optimal results. In addition to the isolated airfoil, this project also investigated the cascade effect of blade elements with a NACA 4415 airfoil profile with different solidities (ranges from 0.05 to 0.4). While the typical range for a 3-blade horizontal wind turbine is from 0.021 to 0.11 [1]. Aerodynamics of the airfoil will be influenced by different solidities.
Convergence of Extreme Loads for Offshore Wind Turbine Support Structures
Stewart, Gordon; Lackner, Matthew; Arwade, Sanjay R.; Myers, Andrew T.; Hallowell, Spencer (Virginia Tech, 2015-06-11)
Extreme loads of wind turbines are historically difficult to predict through simulation due to uncertainty in input conditions as well as in the simulation models. In addition, many long time series must be simulated for the statistics of the peak loads to become stationary. Offshore wind turbines require even more simulation due to the addition of stochastic wave loading. Floating offshore wind turbines, the subject of this paper, experience free-body motion as a result of wind and wave loading, and the phasing of wind turbulence, turbine motion, and large waves can be very influential in determining extreme loading. The International Electrotechnical Commission's 61400-3 standard covers loads analysis of offshore wind turbines, including only cursory references toward floating offshore wind turbines. This IEC design standard requires six 1-hour simulations to estimate extreme loads, which is not long enough for convergence of the statistics of peak loads for offshore turbines, especially floating turbines, which have higher and more variable loads due to platform motion. In this paper, 50-year wind and wave conditions are synthesized from data from the National Oceanographic and Atmospheric Administration's (NOAA's) floating data buoys for a suite of ocean sites suitable for floating or fixed bottom offshore wind turbines. The simulation software used in this paper is FAST, developed by the National Renewable Energy Laboratory, which is a coupled aero-hydro-servo-elastic wind turbine design tool. The current version of FAST which is used in this research includes second-order hydrodynamic effects, which may be important sources of loading in extreme conditions for certain floating platforms. TurbSim is used to create full-field turbulent wind files using the mean wind speed determined from the buoy data, while the hydrodynamics module within FAST handles the wave height time series using a JONSWAP spectrum. The OC3 spar buoy and the OC4 semi-submersible floating platforms are used as examples of realistic platform designs and a monopile is used as the fixed bottom example. A large number of 1-hour simulations are run to determine the convergence characteristics of each platform at each ocean site. These results are discussed and recommendations for future revisions of the design standard are made. Future work concerning various methods that will reduce the simulation cost of determining the converged extreme load will also be discussed.

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