WorldWideScience

Sample records for wind wake effect

  1. Effects of wind turbine wake on atmospheric sound propagation

    DEFF Research Database (Denmark)

    Barlas, Emre; Zhu, Wei Jun; Shen, Wen Zhong

    2017-01-01

    In this paper, we investigate the sound propagation from a wind turbine considering the effects of wake-induced velocity deficit and turbulence. In order to address this issue, an advanced approach was developed in which both scalar and vector parabolic equations in two dimensions are solved. Flow...... field input was obtained using the actuator line (AL) technique with Large Eddy Simulation (LES) to model the wind turbine and its wake and from an analytical wake model. The effect of incoming wind speed and atmospheric stability was investigated with the analytical wake input using a single point...

  2. Wall modeled LES of wind turbine wakes with geometrical effects

    Science.gov (United States)

    Bricteux, Laurent; Benard, Pierre; Zeoli, Stephanie; Moureau, Vincent; Lartigue, Ghislain; Vire, Axelle

    2017-11-01

    This study focuses on prediction of wind turbine wakes when geometrical effects such as nacelle, tower, and built environment, are taken into account. The aim is to demonstrate the ability of a high order unstructured solver called YALES2 to perform wall modeled LES of wind turbine wake turbulence. The wind turbine rotor is modeled using an Actuator Line Model (ALM) while the geometrical details are explicitly meshed thanks to the use of an unstructured grid. As high Reynolds number flows are considered, sub-grid scale models as well as wall modeling are required. The first test case investigated concerns a wind turbine flow located in a wind tunnel that allows to validate the proposed methodology using experimental data. The second test case concerns the simulation of a wind turbine wake in a complex environment (e.g. a Building) using realistic turbulent inflow conditions.

  3. Wind Turbines Wake Aerodynamics

    DEFF Research Database (Denmark)

    Vermeer, L.; Sørensen, Jens Nørkær; Crespo, A.

    2003-01-01

    The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions......, thereby excluding wind shear, wind speed and rotor setting changes and yawed conditions. The emphasis is put on measurements in controlled conditions.For the far wake, the survey focusses on both single turbines and wind farm effects, and the experimental and numerical work are reviewed; the main interest...... is to study how the far wake decays downstream, in order to estimate the effect produced in downstream turbines.The article is further restricted to horizontal axis wind turbines and excludes all other types of turbines....

  4. On the Effects of Wind Turbine Wake Skew Caused by Wind Veer

    Energy Technology Data Exchange (ETDEWEB)

    Churchfield, Matthew J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sirnivas, Senu [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2018-01-12

    Because of Coriolis forces caused by the Earth's rotation, the structure of the atmospheric boundary layer often contains wind-direction change with height, also known as wind-direction veer. Under low turbulence conditions, such as in stably stratified atmospheric conditions, this veer can be significant, even across the vertical extent of a wind turbine's rotor disk. The veer then causes the wind turbine wake to skew as it advects downstream. This wake skew has been observed both experimentally and numerically. In this work, we attempt to examine the wake skewing process in some detail, and quantify how differently a skewed wake versus a non skewed wake affects a downstream turbine. We do this by performing atmospheric large-eddy simulations to create turbulent inflow winds with and without veer. In the veer case, there is a roughly 8 degree wind direction change across the turbine rotor. We then perform subsequent large-eddy simulations using these inflow data with an actuator line rotor model to create wakes. The turbine modeled is a large, modern, offshore, multimegawatt turbine. We examine the unsteady wake data in detail and show that the skewed wake recovers faster than the non skewed wake. We also show that the wake deficit does not skew to the same degree that a passive tracer would if subject to veered inflow. Last, we use the wake data to place a hypothetical turbine 9 rotor diameters downstream by running aeroelastic simulations with the simulated wake data. We see differences in power and loads if this downstream turbine is subject to a skewed or non skewed wake. We feel that the differences observed between the skewed and nonskewed wake are important enough that the skewing effect should be included in engineering wake models.

  5. On the Effects of Wind Turbine Wake Skew Caused by Wind Veer: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Churchfield, Matthew J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sirnivas, Senu [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2018-03-01

    Because of Coriolis forces caused by the Earth's rotation, the structure of the atmospheric boundary layer often contains wind-direction change with height, also known as wind-direction veer. Under low turbulence conditions, such as in stably stratified atmospheric conditions, this veer can be significant, even across the vertical extent of a wind turbine's rotor disk. The veer then causes the wind turbine wake to skew as it advects downstream. This wake skew has been observed both experimentally and numerically. In this work, we attempt to examine the wake skewing process in some detail, and quantify how differently a skewed wake versus a non skewed wake affects a downstream turbine. We do this by performing atmospheric large-eddy simulations to create turbulent inflow winds with and without veer. In the veer case, there is a roughly 8 degree wind direction change across the turbine rotor. We then perform subsequent large-eddy simulations using these inflow data with an actuator line rotor model to create wakes. The turbine modeled is a large, modern, offshore, multimegawatt turbine. We examine the unsteady wake data in detail and show that the skewed wake recovers faster than the non skewed wake. We also show that the wake deficit does not skew to the same degree that a passive tracer would if subject to veered inflow. Last, we use the wake data to place a hypothetical turbine 9 rotor diameters downstream by running aeroelastic simulations with the simulated wake data. We see differences in power and loads if this downstream turbine is subject to a skewed or non skewed wake. We feel that the differences observed between the skewed and nonskewed wake are important enough that the skewing effect should be included in engineering wake models.

  6. Wind Turbine Power Curve Design for Optimal Power Generation in Wind Farms Considering Wake Effect

    DEFF Research Database (Denmark)

    Tian, Jie; Zhou, Dao; Su, Chi

    2017-01-01

    In modern wind farms, maximum power point tracking (MPPT) is widely implemented. Using the MPPT method, each individual wind turbine is controlled by its pitch angle and tip speed ratio to generate the maximum active power. In a wind farm, the upstream wind turbine may cause power loss to its...... downstream wind turbines due to the wake effect. According to the wake model, downstream power loss is also determined by the pitch angle and tip speed ratio of the upstream wind turbine. By optimizing the pitch angle and tip speed ratio of each wind turbine, the total active power of the wind farm can...... be increased. In this paper, the optimal pitch angle and tip speed ratio are selected for each wind turbine by the exhausted search. Considering the estimation error of the wake model, a solution to implement the optimized pitch angle and tip speed ratio is proposed, which is to generate the optimal control...

  7. Impacts of Wake Effect and Time Delay on the Dynamic Analysis of Wind Farms Models

    Science.gov (United States)

    El-Fouly, Tarek H. M.; El-Saadany, Ehab F.; Salama, Magdy M. A.

    2008-01-01

    This article investigates the impacts of proper modeling of the wake effects and wind speed delays, between different wind turbines' rows, on the dynamic performance accuracy of the wind farms models. Three different modeling scenarios were compared to highlight the impacts of wake effects and wind speed time-delay models. In the first scenario,…

  8. Wakes in very large wind farms and the effect of neighbouring wind farms

    International Nuclear Information System (INIS)

    Nygaard, Nicolai Gayle

    2014-01-01

    We present the first analysis of wake losses in some of the largest offshore wind farms built to date. In addition, we give an example of the external wake losses that can be imposed by a neighbouring wind farm. Both situations lend insights to the wake phenomena in large offshore wind farm clusters. A simple wake model is compared to the data to assess the need for a more detailed physical description of large wind farm wakes

  9. Wake Effects on Lifetime Distribution in DFIG-based Wind Farms

    DEFF Research Database (Denmark)

    Tian, Jie; Zhou, Dao; Su, Chi

    2017-01-01

    With the increasing size of the wind farms, the impact of the wake effect on the energy yields and lifetime consumption of wind turbine can no longer be neglected. In this paper, the affecting factors like the wind speed and wind direction are investigated in terms of the single wake and multiple......, and it guides to the optimized control strategies for the balanced reliability....

  10. Analysis of the reduced wake effect for available wind power calculation during curtailment

    NARCIS (Netherlands)

    Sanchez Perez Moreno, S.; Ummels, B. C.; Zaayer, M B

    2017-01-01

    With the increase of installed wind power capacity, the contribution of wind power curtailment to power balancing becomes more relevant. Determining the available power during curtailment at the wind farm level is not trivial, as curtailment changes the wake effects in a wind farm. Current best

  11. Assessment of blockage effects on the wake characteristics and power of wind turbines

    DEFF Research Database (Denmark)

    Sarlak Chivaee, Hamid; Nishino, T.; Martínez-Tossas, L.A.

    2016-01-01

    Large Eddy Simulations (LES) are performed in order to study the wake and power characteristics of a horizontal-axis wind turbine in a wind tunnel. Using an actuator line technique, the effect of wind tunnel blockage ratio (defined as the ratio of the rotor swept area to the tunnel cross-sectiona......Large Eddy Simulations (LES) are performed in order to study the wake and power characteristics of a horizontal-axis wind turbine in a wind tunnel. Using an actuator line technique, the effect of wind tunnel blockage ratio (defined as the ratio of the rotor swept area to the tunnel cross...

  12. Wind Farm Wake

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Karagali, Ioanna; Volker, Patrick

    2017-01-01

    together to investigate the atmospheric conditions at the time of the photos by analysing local meteorological observations and wind turbine information, satellite remote sensing and nearby radiosonde data. Two wake models and one mesoscale model were used to model the case and explain what was seen.......On 25 January 2016 at 12:45 UTC several photographs of the offshore wind farm Horns Rev 2 were taken by helicopter pilot Gitte Lundorff with an iPhone. A very shallow layer of fog covered the sea. The photos of the fog over the sea dramatically pictured the offshore wind farm wake. Researchers got...

  13. Optimal Control to Increase Energy Production of Wind Farm Considering Wake Effect and Lifetime Estimation

    DEFF Research Database (Denmark)

    Tian, Jie; Zhou, Dao; Su, Chi

    2017-01-01

    as an example. Due to the small range of the effective wake area, it is found that the energy production is almost the same. Finally, the pitch angle curve and active power curve are optimized according to the Maximum Energy Production (MEP) of a wind farm. Upon considering and contrasting the MPPT method...... to maximize the energy production of wind farms by considering the wake effect and the lifetime of wind turbine. It starts with the analysis of the pitch angle curve and active power curve seen from the Maximum Power Point Tracking (MPPT) of individual wind turbines. Taking the wake effect into account......, the pitch angle curve and active power curve are optimized with the aim of Maximum Power Generation (MPG) of the wind farm. Afterwards, considering the lifetime of wind turbines, a comparison is offered between the MPPT method and the MPG method for energy production using a simplified two-turbine wind farm...

  14. Roughness Effects on Wind-Turbine Wake Dynamics in a Boundary-Layer Wind Tunnel

    DEFF Research Database (Denmark)

    Barlas, Emre; Buckingham, Sophia; van Beeck, Jeroen

    2016-01-01

    Increasing demand in wind energy has resulted in increasingly clustered wind farms, and raised the interest in wake research dramatically in the last couple of years. To this end, the present work employs an experimental approach with scaled three-bladed wind-turbine models in a large boundary-la...

  15. Effects of Freestream Turbulence in a Model Wind Turbine Wake

    Directory of Open Access Journals (Sweden)

    Yaqing Jin

    2016-10-01

    Full Text Available The flow structure in the wake of a model wind turbine is explored under negligible and high turbulence in the freestream region of a wind tunnel at R e ∼ 7 × 10 4 . Attention is placed on the evolution of the integral scale and the contribution of the large-scale motions from the background flow. Hotwire anemometry was used to obtain the streamwise velocity at various streamwise and spanwise locations. The pre-multiplied spectral difference of the velocity fluctuations between the two cases shows a significant energy contribution from the background turbulence on scales larger than the rotor diameter. The integral scale along the rotor axis is found to grow linearly with distance, independent of the incoming turbulence levels. This scale appears to reach that of the incoming flow in the high turbulence case at x / d ∼ 35–40. The energy contribution from the turbine to the large-scale flow structures in the low turbulence case increases monotonically with distance. Its growth rate is reduced past x / d ∼ 6–7. There, motions larger than the rotor contribute ∼ 50 % of the total energy, suggesting that the population of large-scale motions is more intense in the intermediate field. In contrast, the wake in the high incoming turbulence is quickly populated with large-scale motions and plateau at x / d ∼ 3 .

  16. Development of Wind Farm AEP Prediction Program Considering Directional Wake Effect

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Kyoungboo; Cho, Kyungho; Huh, Jongchul [Jeju Nat’l Univ., Jeju (Korea, Republic of)

    2017-07-15

    For accurate AEP prediction in a wind farm, it is necessary to effectively calculate the wind speed reduction and the power loss due to the wake effect in each wind direction. In this study, a computer program for AEP prediction considering directional wake effect was developed. The results of the developed program were compared with the actual AEP of the wind farm and the calculation result of existing commercial software to confirm the accuracy of prediction. The applied equations are identical with those of commercial software based on existing theories, but there is a difference in the calculation process of the detection of the wake effect area in each wind direction. As a result, the developed program predicted to be less than 1% of difference to the actual capacity factor and showed more than 2% of better results compared with the existing commercial software.

  17. Effect of atmospheric turbulence on wind turbine wakes: An LES study

    Science.gov (United States)

    Wu, Y. T.; Porté-Agel, F.

    2012-04-01

    A comprehensive numerical study of atmospheric turbulence effect on wind-turbine wakes is presented. Large-eddy simulations of neutrally-stratified boundary layers developed over different flat surfaces (forest, farmland, grass, and snow) are performed to investigate the structure of turbine wakes in cases where the incident flows to the wind turbine have the same mean velocity at the hub height but different mean wind shears and turbulence intensity levels. The simulation results show that the different wind shears and turbulence intensity levels of the incoming flow lead to considerable influence on the spatial distribution of the mean velocity deficit, turbulence intensity, and turbulent shear stress in the wake region downstream of the turbine. In general, the recovery of the turbine-induced wake (velocity deficit) is faster and the turbulence intensity level is higher and has its maximum closer to the turbine for wakes of turbines over rougher terrain. In order to isolate the effect of turbulence intensity from that of wind shear, simulations have also been performed with synthetic inflow velocity fields that have the same mean wind shear but different turbulence intensity levels. We find that the effect of the inflow turbulence intensity on the wake recovery and turbulence levels is stronger than that of the mean shear.

  18. Simulation of wake effects between two wind farms

    DEFF Research Database (Denmark)

    Hansen, Kurt Schaldemose; Réthoré, Pierre-Elouan; Palma, Jose

    2015-01-01

    SCADA data, recorded on the downstream wind farm, has been used to identify flow cases with visible clustering effects. The inflow condition is derived from a partly undisturbed wind turbine, due to lack of mast measurements. The SCADA data analysis concludes that centre of the deficit for the do...

  19. Simulation of wake effects between two wind farms

    International Nuclear Information System (INIS)

    Hansen, K S; Réthoré, P-E; Peña, A; Ott, S; Van der Laan, M P; Volker, P; Palma, J; Hevia, B G; Prospathopoulos, J; Schepers, G; Palomares, A

    2015-01-01

    SCADA data, recorded on the downstream wind farm, has been used to identify flow cases with visible clustering effects. The inflow condition is derived from a partly undisturbed wind turbine, due to lack of mast measurements. The SCADA data analysis concludes that centre of the deficit for the downstream wind farm with disturbed inflow has a distinct visible maximum deficit zone located only 5-10D downstream from the entrance. This zone, representing 20-30% speed reduction, increases and moves downstream for increasing cluster effect and is not visible outside a flow sector of 20-30°. The eight flow models represented in this benchmark include both RANS models, mesoscale models and engineering models. The flow cases, identified according to the wind speed level and inflow sector, have been simulated and validated with the SCADA results. The model validation concludes that all models more or less are able to predict the location and size of the deficit zone inside the downwind wind farm. (paper)

  20. Effect of Wind Turbine Wakes on the Performance of a Real Case WRF-LES Simulation

    Science.gov (United States)

    Doubrawa, P.; Montornès, A.; Barthelmie, R. J.; Pryor, S. C.; Giroux, G.; Casso, P.

    2017-05-01

    The main objective of this work is to estimate how much of the discrepancy between measured and modeled flow parameters can be attributed to wake effects. The real case simulations were performed for a period of 15 days with the Weather Research and Forecasting (WRF) model and nested down to a Large-Eddy Simulation (LES) scale of ∼ 100 m. Beyond the coastal escarpment, the site is flat and homogeneous and the study focuses on a meteorological mast and a northern turbine subjected to the wake of a southern turbine. The observational data set collected during the Prince Edward Island Wind Energy Experiment (PEIWEE) includes a sonic anemometer at 60 m mounted onto the mast, and measurements from the two turbines. Wake versus free stream conditions are distinguished based on measured wind direction while assuming constant expansion for the wake of the southern turbine. During the period considered the mast and northern turbine were under the southern turbine wake ∼ 16% and ∼ 11% of the time, respectively. Under these conditions, the model overestimates the wind speed and underestimates the turbulence intensity at the mast but not at the northern turbine, where the effect of wakes on the model error is unclear and other model limitations are likely more important. The wind direction difference between the southern and northern turbines is slightly underestimated by the model regardless of whether free stream or wake conditions are observed, indicating that it may be due to factors unrelated to the wake development such as surface forcings. Finally, coupling an inexpensive wake model to the high-fidelity simulation as a post-processing tool drives the simulated wind speeds at the mast significantly closer to the observed values, but the opposite is true at the coastal turbine which is in the far wake. This indicates that the application of a post-processing wake correction should be performed with caution and may increase the wind speed errors when other important

  1. Wake Effects of Large Offshore Wind Farms - a study of the Mesoscale Atmophere

    DEFF Research Database (Denmark)

    Volker, Patrick

    efficiency and the wind farm’s wake recovery to different atmospheric conditions aloft were found in an idealised case study. Moreover, the wind farm efficiency to different climates for wind farm sizes up to 375 km2 was examined. The modelled production varied with wind climate and were well above 1Wm−2......The power production contribution to the power system from offshore wind energy is continuously increasing in the northern European countries. A better understanding of the influence of wind farms to those downstream and to the lower atmosphere will help optimising energy production from large wind...... farm clusters. Mesoscale models allow the simulation of large domains sufficiently to capture large wind farms and surroundings at reasonable computational costs, but processes below the horizontal resolution remain unresolved and have to be parametrised, such as the effects of the wind turbines...

  2. Wake flow characteristics at high wind speed

    DEFF Research Database (Denmark)

    Aagaard Madsen, Helge; Larsen, Torben J.; Larsen, Gunner Chr.

    2016-01-01

    Wake flow characteristic at high wind speeds is the main subject of this paper. Although the wake losses decrease at high wind speeds it has been found in a recent study that for multiple wake inflow the increase in loading due to wake effects are substantial even at wind speeds well above rated...... power. In the present study we simulate the wake flow for a row of turbines with the wind aligned with the row using a simplified approach. The velocity deficit, being a function of the thrust coefficient, is simulated based on the BEM solution for wake expansion. An axis-symmetric boundary layer...... equation model (the same as implemented in the DWM model) is subsequently used to develop the deficit down to the next turbine, and then the approach is successively repeated. Simulation results for four different spacing’s in a row with eight turbines show that there are two major flow regimes...

  3. Wake dynamics in offshore wind farms

    DEFF Research Database (Denmark)

    de Mare, Martin Tobias

    Wind turbines within offshore wind farms spend considerable time operating in the wake of neighboring wind turbines. An important contribution to the loads on a wake-affected wind turbine is the slow movement of the wake from the upstream wind turbine across the rotor of the wake-affected wind...

  4. Reactive Power Dispatch Method in Wind Farms to Improve the Lifetime of Power Converter Considering Wake Effect

    DEFF Research Database (Denmark)

    Tian, Jie; Zhou, Dao; Su, Chi

    2017-01-01

    In Wind Farms (WF), the most popular and commonly implemented active power control method is the Maximum Power Point Tracking (MPPT). Due to the wake effect, the upstream Wind Turbine (WT) in WFs has more active power generation than the downstream WT at the wind directions and wind speeds...

  5. Comparison of the effectiveness of analytical wake models for wind farm with constant and variable hub heights

    International Nuclear Information System (INIS)

    Wang, Longyan; Tan, Andy C.C.; Cholette, Michael; Gu, Yuantong

    2016-01-01

    Highlights: • The effectiveness of three analytical wake models is studied. • The results of the analytical wake models are compared with the CFD simulations. • The results of CFD simulation are verified by comparison to the offshore wind farm observation data. • The onshore wind farm with both constant and different hub height turbines are analyzed. • PARK model is able to predict the total wind farm power production well with tuned surface roughness value. - Abstract: Extensive power losses of wind farm have been witnessed due to the wake interactions between wind turbines. By applying analytical wake models which describe the wind speed deficits in the wake quantitatively, the power losses can be regained to a large extent through wind farm layout optimization, and this has been extensively reported in literature. Nevertheless, the effectiveness of the analytical wake models in predicting the wind farm power production have rarely been studied and compared for wind farm with both constant and variable wind turbine hub heights. In this study, the effectiveness of three different analytical wake models (PARK model, Larsen model and B-P model) is thoroughly compared over a wide range of wake properties. After the validation with the observation data from offshore wind farm, CFD simulations are used to verify the effectiveness of the analytical wake models for an onshore wind farm. The results show that when using the PARK model the surface roughness value (z 0 ) must be carefully tuned to achieve good performance in predicting the wind farm power production. For the other two analytical wake models, their effectiveness varies depending on the situation of wind farm (offshore or onshore) and the wind turbine hub heights (constant or variable). It was found that the results of B-P model agree well with the CFD simulations for offshore wind farm, but not for the onshore wind farm. The Larsen model is more accurate for the wind farm with variable wind turbine

  6. Experimental Study on the Effects of Winglets on the Wake of a Model Wind Turbine

    Science.gov (United States)

    Tobin, Nicolas; Hamed, Ali M.; Chamorro, Leonardo P.

    2015-11-01

    Wind tunnel particle image velocimetry was used to investigate the effects of winglets on the wake dynamics of a model wind turbine. The behavior of a turbine with downstream-facing winglets was compared with a turbine without winglets. The turbines were placed in a turbulent boundary layer that reached up to the hub height, allowing for investigation of behavior in both turbulent and uniform flow. The winglets did not significantly change the strength of the tip vortices in the region of uniform incoming flow. The tip vortices in the more turbulent region, however, decayed much faster, diminishing to near-zero within the first ~1.5 rotor diameters, whereas the upper tip vortices persisted potentially up to ~4 rotor diameters. The winglets also increased the power coefficient by 7.5 %, while increasing the coefficient of thrust by 10.0 %. The higher coefficient of thrust created a region of enhanced mean shear in the outer portion of the wake, leading to increased turbulence statistics in the far wake. The wingletted turbine had a similar wake deficit at 5 rotor diameters as the base turbine did at 1.5 rotor diameters, with potential implications for using wingletted turbines in wind farms.

  7. Effects of a three-dimensional hill on the wake characteristics of a model wind turbine

    Science.gov (United States)

    Yang, Xiaolei; Howard, Kevin B.; Guala, Michele; Sotiropoulos, Fotis

    2015-02-01

    The spatial evolution of a turbine wake downwind of a three-dimensional sinusoidal hill is studied using large-eddy simulations and wind tunnel measurements. The computed flow fields behind the hill show good agreement with wind tunnel measurements. Three different heights of the hill, i.e., hhill = zh - 0.5D, ≈ zh and =zh + 0.5D (where zh is the turbine hub height and D is the diameter of the turbine rotor), were considered. The effect of the hill turbine spacing was investigated through a comparative analysis with the turbine wake results in the undisturbed turbulent boundary layer. It is observed that the turbine wakes downwind of the hill with hhill ≈ zh and hhill = zh + 0.5D recover faster because of the increased entrainment of ambient flow into the turbine wake, which is due to the enhanced turbulent transport in both spanwise and vertical directions. In comparison with the turbine only case, significant increases in the turbulence kinetic energy (TKE) in the turbine wake are observed for the hill-turbine cases with hhill ≈ zh and hhill = zh + 0.5D. A velocity scale UT, defined in terms of the thrust force acting on the turbine, is introduced for the turbine-added velocity deficit and TKE. For the turbine-added velocity deficit, UT is shown to be an appropriate scale at wake locations sufficiently far downwind of the turbine (i.e., greater than or equal to 8D). The vertical profiles of the turbine-added TKE normalized by UT 2 are shown to nearly collapse in the wake both for the turbine only and hill-turbine cases at all locations greater than 4D downwind of the turbine. A simple model for the turbine-added TKE in complex terrain is also proposed based on the new physical insights obtained from our simulations.

  8. Wake-Effect Minimising Optimal Control of Wind Farms, with Load Reduction

    DEFF Research Database (Denmark)

    Borchersen, Anders Bech; Larsen, Jesper Abildgaard; Sivabalan, Senthuran

    2014-01-01

    A power generating wind turbine causes a speed reduction and an added turbulence to the wind. Wind turbines in wind farms are often caught in these wakes and are found to have a higher structural load than non affected wind turbines. This article investigates the possibility of designing a contro...

  9. Two improvements to the dynamic wake meandering model: including the effects of atmospheric shear on wake turbulence and incorporating turbulence build-up in a row of wind turbines

    DEFF Research Database (Denmark)

    Keck, Rolf-Erik; de Mare, Martin Tobias; Churchfield, Matthew J.

    2015-01-01

    The dynamic wake meandering (DWM) model is an engineering wake model designed to physically model the wake deficit evolution and the unsteady meandering that occurs in wind turbine wakes. The present study aims at improving two features of the model: The effect of the atmospheric boundary layer s...

  10. Probabilistic Approach to Optimizing Active and Reactive Power Flow in Wind Farms Considering Wake Effects

    Directory of Open Access Journals (Sweden)

    Yong-Cheol Kang

    2013-10-01

    Full Text Available This paper presents a novel probabilistic optimization algorithm for simultaneous active and reactive power dispatch in power systems with significant wind power integration. Two types of load and wind-speed uncertainties have been assumed that follow normal and Weibull distributions, respectively. A PV bus model for wind turbines and the wake effect for correlated wind speed are used to achieve accurate AC power flow analysis. The power dispatch algorithm for a wind-power integrated system is modeled as a probabilistic optimal power flow (P-OPF problem, which is operated through fixed power factor control to supply reactive power. The proposed P-OPF framework also considers emission information, which clearly reflects the impact of the energy source on the environment. The P-OPF was tested on a modified IEEE 118-bus system with two wind farms. The results show that the proposed technique provides better system operation performance evaluation, which is helpful in making decisions about power system optimal dispatch under conditions of uncertainty.

  11. Wake effects in Alsvik wind park: Comparison between measurements and predictions

    Energy Technology Data Exchange (ETDEWEB)

    Magnusson, Mikael [Uppsala Univ. (Sweden). Dept. of Meteorology; Rados, K.G.; Pothou, K.P. [National Technical Univ., Athen (Greece). Fluid section

    1996-12-01

    In this paper characteristic parameters in a wind turbine wake are studied. The data used are full-scale measurements from a wind farm in Sweden, Alsvik, and results from a numerical model calculated for the same site. The results are valid for neutral stratification. The model employs a particle-vortex approach at the rotor plane, a Navier-Stokes solver in the near wake and applies self preservation in the far wake. The parameters investigated are the relative velocity deficit at centre line and hub height, and the radial distribution of the turbulent kinetic energy. 6 refs, 9 figs

  12. Wind Wake Watcher v. 1.0

    Energy Technology Data Exchange (ETDEWEB)

    2017-10-03

    This software enables the user to produce Google Earth visualizations of turbine wake effects for wind farms. The visualizations are based on computations of statistical quantities that vary with wind direction and help quantify the effects on power production of upwind turbines on turbines in their wakes. The results of the software are plot images and kml files that can be loaded into Google Earth. The statistics computed are described in greater detail in the paper: S. Martin, C. H. Westergaard, and J. White (2016), Visualizing Wind Farm Wakes Using SCADA Data, in Wither Turbulence and Big Data in the 21st Century? Eds. A. Pollard, L. Castillo, L. Danaila, and M. Glauser. Springer, pgs. 231-254.

  13. Effect of chord-to-diameter ratio on vertical-axis wind turbine wake development

    Science.gov (United States)

    Parker, Colin M.; Araya, Daniel B.; Leftwich, Megan C.

    2017-12-01

    The wake structure of a vertical-axis wind turbine (VAWT) is strongly dependent on the tip-speed ratio, λ, or the tangential speed of the turbine blade relative to the incoming wind speed. The geometry of a turbine can influence λ, but the precise relationship among VAWT geometric parameters and VAWT wake characteristics remains unknown. To investigate this relationship, we present the results of an experiment to characterize the wakes of three VAWTs that are geometrically similar except for the ratio of the turbine diameter ( D), to blade chord ( c), which was chosen to be D/c = 3, 6, and 9. For a fixed freestream Reynolds number based on the blade chord of Re_c = 1.6× 10^3, both two-component particle image velocimetry (PIV) and single-component hot-wire anemometer measurements are taken at the horizontal mid-plane in the wake of each turbine. PIV measurements are ensemble averaged in time and phase averaged with each rotation of the turbine. Hot-wire measurement points are selected to coincide with the edge of the shear layer of each turbine wake, as deduced from the PIV data, which allows for an analysis of the frequency content of the wake due to vortex shedding by the turbine.

  14. Evaluation of wind farm efficiency and wind turbine wakes at the Nysted offshore wind farm

    DEFF Research Database (Denmark)

    Barthelmie, Rebecca Jane; Jensen, L.E.

    2010-01-01

    be quantified, albeit with relatively large uncertainty due to stochastic effects in the data. There is evidence of the ‘deep array effect’ in that wake losses in the centre of the wind farm are under-estimated by the wind farm model WAsP, although overall efficiency of the wind farm is well predicted due......Here, we quantify relationships between wind farm efficiency and wind speed, direction, turbulence and atmospheric stability using power output from the large offshore wind farm at Nysted in Denmark. Wake losses are, as expected, most strongly related to wind speed variations through the turbine...... thrust coefficient; with direction, atmospheric stability and turbulence as important second order effects. While the wind farm efficiency is highly dependent on the distribution of wind speeds and wind direction, it is shown that the impact of turbine spacing on wake losses and turbine efficiency can...

  15. Wake effects of large offshore wind farms on the mesoscale atmosphere

    DEFF Research Database (Denmark)

    Volker, Patrick; Badger, Jake; Hahmann, Andrea N.

    to the fact that its typical horizontal grid spacing is on the order of 2km, the energy extracted by the turbine, as well as the wake development inside the turbine-containing grid-cells, are not described explicitly, but are parametrized as another sub-grid scale process. In order to appropriately capture...... the wind farm wake recovery and its direction, two properties are important, the total energy extracted by the wind farm and its velocity deficit distribution. In the considered parametrization the individual turbines apply a thrust dependent on a local sub grid scale velocity, which is influenced...... by the up-stream turbines. For the sub-grid scale velocity deficit, the entrainment from the free atmospheric flow into the wake region, is taken into account. Furthermore, since the model horizontal distance is several times larger then the turbine diameter, it has been assumed that the generated...

  16. Large Eddy Simulation of Vertical Axis Wind Turbine wakes; Part II: effects of inflow turbulence

    Science.gov (United States)

    Duponcheel, Matthieu; Chatelain, Philippe; Caprace, Denis-Gabriel; Winckelmans, Gregoire

    2017-11-01

    The aerodynamics of Vertical Axis Wind Turbines (VAWTs) is inherently unsteady, which leads to vorticity shedding mechanisms due to both the lift distribution along the blade and its time evolution. Large-scale, fine-resolution Large Eddy Simulations of the flow past Vertical Axis Wind Turbines have been performed using a state-of-the-art Vortex Particle-Mesh (VPM) method combined with immersed lifting lines. Inflow turbulence with a prescribed turbulence intensity (TI) is injected at the inlet of the simulation from a precomputed synthetic turbulence field obtained using the Mann algorithm. The wake of a standard, medium-solidity, H-shaped machine is simulated for several TI levels. The complex wake development is captured in details and over long distances: from the blades to the near wake coherent vortices, then through the transitional ones to the fully developed turbulent far wake. Mean flow and turbulence statistics are computed over more than 10 diameters downstream of the machine. The sensitivity of the wake topology and decay to the TI level is assessed.

  17. Wakes in large offshore wind farms

    DEFF Research Database (Denmark)

    Berthelmie, Rebecca J.; Frandsen, Sten Tronæs; Rathmann, Ole

    2008-01-01

    Power losses due to wind turbine wakes are of the order of 10 and 20% of total power output in large wind farms. The focus of this research carried out within the EC funded UPWIND project is wind speed and turbulence modelling for large wind farms/wind turbines in complex terrain and offshore...... in order to optimise wind farm layouts to reduce wake losses and loads. For complex terrain, a set of three evaluations is underway. The first is a model comparison for a Gaussian Hill where CFD models and wind farm models are being compared for the case of one hilltop wind turbine. The next case...... is for five turbines in flat terrain. Finally a complex terrain wind farm will be modelled and compared with observations. For offshore wind farms, the focus is on cases at the Horns Rev wind farm which indicate wind farm models require modification to reduce under-prediction of wake losses while CFD models...

  18. Dynamic Mode Decomposition Analysis of Wind Turbine Wakes

    Science.gov (United States)

    Thomas, Vaughan; Verhulst, Claire; Meneveau, Charles; Gayme, Dennice

    2015-11-01

    In this work we explore the use of dynamic mode decomposition (DMD) to analyze three dimensional large eddy simulations (LES) of wind farms in order to isolate the temporal characteristics of key flow structures. There are a number of variants of DMD that each produce a reduced order linear system that approximates the dynamics of the original system. Here, we are interested in finding the lowest order system which captures the wake dynamics and other essential flow features. When DMD is applied to wake regions of LES of wind farms, the results isolate the mean wake and flow structures whose oscillation determines the meandering behavior of the wake. This ability to capture the wake dynamics has important implications for wind farm modeling and control as they permit the construction of time-varying wake models that can capture time-varying effects such as wake meandering. We gratefully acknowledge support from NSF grant IIA-121243482 (WINDINSPIRE).

  19. Meteorological Controls on Wind Turbine Wakes

    DEFF Research Database (Denmark)

    Barthelmie, Rebecca J.; Hansen, Kurt Schaldemose; Pryor, S.C.

    2013-01-01

    The primary control on the magnitude of the power losses induced by wind turbine wakes in large wind farms is the hub-height wind speed via its link to the turbine thrust coefficient. Hence, at low to moderate wind speeds (between cut-in and rated turbine wind speeds) when the thrust coefficient ...

  20. Wake effect on a uniform flow behind wind-turbine model

    DEFF Research Database (Denmark)

    Okulov, Valery; Naumov, I. V.; Mikkelsen, Robert Flemming

    2015-01-01

    LDA experiments were carried out to study the development of mean velocity profiles of the very far wake behind a wind turbine model in a water flume. The model of the rotor is placed in a middle of the flume. The initial flume flow is subjected to a very low turbulence level, limiting the influe......LDA experiments were carried out to study the development of mean velocity profiles of the very far wake behind a wind turbine model in a water flume. The model of the rotor is placed in a middle of the flume. The initial flume flow is subjected to a very low turbulence level, limiting...... the influence of external disturbances on the development of the inherent wake instability. The rotor is three-bladed and designed using Glauert’s optimum theory at a tip speed ratio λ =5 with a constant of the lift coefficient along the span, CL= 0.8. The wake development has been studied in the range of tip...

  1. Wind Turbine Wake-Redirection Control at the Fishermen's Atlantic City Windfarm: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Churchfield, M.; Fleming, P.; Bulder, B.; White, S.

    2015-05-06

    In this paper, we will present our work towards designing a control strategy to mitigate wind turbine wake effects by redirecting the wakes, specifically applied to the Fishermen’s Atlantic City Windfarm (FACW), proposed for deployment off the shore of Atlantic City, New Jersey. As wind turbines extract energy from the air, they create low-speed wakes that extend behind them. Full wake recovery Full wake recovery to the undisturbed wind speed takes a significant distance. In a wind energy plant the wakes of upstream turbines may travel downstream to the next row of turbines, effectively subjecting them to lower wind speeds, meaning these waked turbines will produce less power.

  2. An analysis of offshore wind farm SCADA measurements to identify key parameters influencing the magnitude of wake effects

    Science.gov (United States)

    Mittelmeier, N.; Blodau, T.; Steinfeld, G.; Rott, A.; Kühn, M.

    2016-09-01

    Atmospheric conditions have a clear influence on wake effects. Stability classification is usually based on wind speed, turbulence intensity, shear and temperature gradients measured partly at met masts, buoys or LiDARs. The objective of this paper is to find a classification for stability based on wind turbine Supervisory Control and Data Acquisition (SCADA) measurements in order to fit engineering wake models better to the current ambient conditions. Two offshore wind farms with met masts have been used to establish a correlation between met mast stability classification and new aggregated statistical signals based on multiple measurement devices. The significance of these new signals on power production is demonstrated for two wind farms with met masts and validated against data from one further wind farm without a met mast. We found a good correlation between the standard deviation of active power divided by the average power of wind turbines in free flow with the ambient turbulence intensity when the wind turbines were operating in partial load.

  3. Wind shear estimation and wake detection by rotor loads — First wind tunnel verification

    Science.gov (United States)

    Schreiber, J.; Cacciola, S.; Campagnolo, F.; Petrović, V.; Mourembles, D.; Bottasso, C. L.

    2016-09-01

    The paper describes a simple method for detecting presence and location of a wake affecting a downstream wind turbine operating in a wind power plant. First, the local wind speed and shear experienced by the wind turbine are estimated by the use of rotor loads and other standard wind turbine response data. Then, a simple wake deficit model is used to determine the lateral position of the wake with respect to the affected rotor. The method is verified in a boundary layer wind tunnel using two instrumented scaled wind turbine models, demonstrating its effectiveness.

  4. Using the coupled wake boundary layer model to evaluate the effect of turbulence intensity on wind farm performance

    NARCIS (Netherlands)

    Stevens, Richard Johannes Antonius Maria; Gayme, Dennice F.; Meneveau, Charles

    2015-01-01

    We use the recently introduced coupled wake boundary layer (CWBL) model to predict the e ect of turbulence intensity on the performance of a wind farm. The CWBL model combines a standard wake model with a \\top-down" approach to get improved predictions for the power output compared to a stand-alone

  5. Offshore and onshore wind turbine wake meandering studied in an ABL wind tunnel

    DEFF Research Database (Denmark)

    Barlas, Emre; Buckingham, Sophia; Glabeke, Gertjan

    2015-01-01

    Scaled wind turbine models have been installed in the VKI L1-B atmospheric boundary layer wind tunnel at offshore and onshore conditions. Time-resolved measurements were carried out with three component hot wire anemometry and stereo-PIV in the middle vertical plane of the wake up to eleven turbine...... spectrum, present in the entire wake mainly for offshore inflow condition. It was found that the Strouhal number, based on the rotor diameter and the wind velocity at hub height, was in the order of 0.25. Below the meandering frequency, turbulence power spectrum decreased, whereas above it increased. Wake...... diameter downstream. The results show an earlier wake recovery for the onshore case. The effect of inflow conditions and the wind turbine’s working conditions on wake meandering was investigated. Wake meandering was detected by hot wire anemometry through a low frequency peak in the turbulent power...

  6. Wind turbine wake measurement in complex terrain

    DEFF Research Database (Denmark)

    Hansen, Kurt Schaldemose; Larsen, Gunner Chr.; Menke, Robert

    2016-01-01

    SCADA data from a wind farm and high frequency time series measurements obtained with remote scanning systems have been analysed with focus on identification of wind turbine wake properties in complex terrain. The analysis indicates that within the flow regime characterized by medium to large...

  7. Wind Farm Wake Models From Full Scale Data

    DEFF Research Database (Denmark)

    Knudsen, Torben; Bak, Thomas

    2012-01-01

    on real full scale data. The modelling is based on so called effective wind speed. It is shown that there is a wake for a wind direction range of up to 20 degrees. Further, when accounting for the wind direction it is shown that the two model structures considered can both fit the experimental data......This investigation is part of the EU FP7 project “Distributed Control of Large-Scale Offshore Wind Farms”. The overall goal in this project is to develop wind farm controllers giving power set points to individual turbines in the farm in order to minimise mechanical loads and optimise power. One...... control configuration examined is distributed control where turbines only communicate with their nearest upwind neighbors. Design of such controllers needs wake models and these models should ideally be distributed. This paper compares two simple multiple wake models for this purpose. The study is based...

  8. Wind turbine wake characterization using long-range Doppler lidar

    Science.gov (United States)

    Aitken, M.; Lundquist, J. K.; Hestmark, K.; Banta, R. M.; Pichugina, Y.; Brewer, A.

    2012-12-01

    techniques are developed to distinguish wakes from the background variability, and moreover, wakes are then classified by width, height, length, and velocity deficit based on atmospheric stability and inflow conditions. By integrating these advanced observational capabilities with innovative approaches to atmospheric modeling, this work will help to improve simulation tools used to quantify power loss and fatigue loading due to wake effects, thereby aiding the optimization of wind farm layouts.

  9. Doppler lidar investigation of wind turbine wake characteristics and atmospheric turbulence under different surface roughness.

    Science.gov (United States)

    Zhai, Xiaochun; Wu, Songhua; Liu, Bingyi

    2017-06-12

    Four field experiments based on Pulsed Coherent Doppler Lidar with different surface roughness have been carried out in 2013-2015 to study the turbulent wind field in the vicinity of operating wind turbine in the onshore and offshore wind parks. The turbulence characteristics in ambient atmosphere and wake area was analyzed using transverse structure function based on Plane Position Indicator scanning mode. An automatic wake processing procedure was developed to determine the wake velocity deficit by considering the effect of ambient velocity disturbance and wake meandering with the mean wind direction. It is found that the turbine wake obviously enhances the atmospheric turbulence mixing, and the difference in the correlation of turbulence parameters under different surface roughness is significant. The dependence of wake parameters including the wake velocity deficit and wake length on wind velocity and turbulence intensity are analyzed and compared with other studies, which validates the empirical model and simulation of a turbine wake for various atmosphere conditions.

  10. Synthetic atmospheric turbulence and wind shear in large eddy simulations of wind turbine wakes

    DEFF Research Database (Denmark)

    Keck, Rolf-Erik; Mikkelsen, Robert Flemming; Troldborg, Niels

    2014-01-01

    of the synthetic methods is found to be adequate to model atmospheric turbulence, and the wake flow results of the model are in good agreement with field data. An investigation is also carried out to estimate the wake transport velocity, used to model wake meandering in lower-order models. The conclusion......A method of generating a synthetic ambient wind field in neutral atmosphere is described and verified for modelling the effect of wind shear and turbulence on a wind turbine wake using the flow solver EllipSys3D. The method uses distributed volume forces to represent turbulent fluctuations...... is that the appropriate transport velocity of the wake lies somewhere between the centre velocity of the wake deficit and the free stream velocity. Copyright © 2013 John Wiley & Sons, Ltd....

  11. Wake flow control using a dynamically controlled wind turbine

    Science.gov (United States)

    Castillo, Ricardo; Wang, Yeqin; Pol, Suhas; Swift, Andy; Hussain, Fazle; Westergaard, Carsten; Texas Tech University Team

    2016-11-01

    A wind tunnel based "Hyper Accelerated Wind Farm Kinematic-Control Simulator" (HAWKS) is being built at Texas Tech University to emulate controlled wind turbine flow physics. The HAWKS model turbine has pitch, yaw and speed control which is operated in real model time, similar to that of an equivalent full scale turbine. Also, similar to that of a full scale wind turbine, the controls are developed in a Matlab Simulink environment. The current diagnostic system consists of power, rotor position, rotor speed measurements and PIV wake characterization with four cameras. The setup allows up to 7D downstream of the rotor to be mapped. The purpose of HAWKS is to simulate control strategies at turnaround times much faster than CFD and full scale testing. The fundamental building blocks of the simulator have been tested, and demonstrate wake steering for both static and dynamic turbine actuation. Parameters which have been studied are yaw, rotor speed and combinations hereof. The measured wake deflections for static yaw cases are in agreement with previously reported research implying general applicability of the HAWKS platform for the purpose of manipulating the wake. In this presentation the general results will be introduced followed by an analysis of the wake turbulence and coherent structures when comparing static and dynamic flow cases. The outcome of such studies could ultimately support effective wind farm wake flow control strategies. Texas Emerging Technology Fund (ETF).

  12. Wind turbine wake in atmospheric turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Rethore, P.-E.

    2009-10-15

    This thesis describes the different steps needed to design a steady-state computational fluid dynamics (CFD) wind farm wake model. The ultimate goal of the project was to design a tool that could analyze and extrapolate systematically wind farm measurements to generate wind maps in order to calibrate faster and simpler engineering wind farm wake models. The most attractive solution was the actuator disc method with the steady state k-epsilon turbulence model. The first step to design such a tool is the treatment of the forces. This thesis presents a computationally inexpensive method to apply discrete body forces into the finite-volume flow solver with collocated variable treatment (EllipSys), which avoids the pressure-velocity decoupling issue. The second step is to distribute the body forces in the computational domain accordingly to rotor loading. This thesis presents a generic flexible method that associates any kind of shapes with the computational domain discretization. The special case of the actuator disc performs remarkably well in comparison with Conway's heavily loaded actuator disc analytical solution and a CFD full rotor computation, even with a coarse discretization. The third step is to model the atmospheric turbulence. The standard k-epsilon model is found to be unable to model at the same time the atmospheric turbulence and the actuator disc wake and performs badly in comparison with single wind turbine wake measurements. A comparison with a Large Eddy Simulation (LES) shows that the problem mainly comes from the assumptions of the eddy-viscosity concept, which are deeply invalidated in the wind turbine wake region. Different models that intent to correct the k-epsilon model's issues are investigated, of which none of them is found to be adequate. The mixing of the wake in the atmosphere is a deeply non-local phenomenon that is not handled correctly by an eddy-viscosity model such as k-epsilon. (author)

  13. Validation of the Eddy Viscosity and Lange Wake Models using Measured Wake Flow Characteristics Behind a Large Wind Turbine Rotor

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Sang Hyeon; Kim, Bum Suk; Huh, Jong Chul [Jeju National Univ., Jeju (Korea, Republic of); Go, Young Jun [Hanjin Ind, Co., Ltd., Yangsan (Korea, Republic of)

    2016-01-15

    The wake effects behind wind turbines were investigated by using data from a Met Mast tower and the SCADA (Supervisory Control and Data Acquisition) system for a wind turbine. The results of the wake investigations and predicted values for the velocity deficit based on the eddy viscosity model were compared with the turbulence intensity from the Lange model. As a result, the velocity deficit and turbulence intensity of the wake increased as the free stream wind speed decreased. In addition, the magnitude of the velocity deficit for the center of the wake using the eddy viscosity model was overestimated while the turbulence intensity from the Lange model showed similarities with measured values.

  14. On wake modeling, wind-farm gradients, and AEP predictions at the Anholt wind farm

    Directory of Open Access Journals (Sweden)

    A. Peña

    2018-04-01

    Full Text Available We investigate wake effects at the Anholt offshore wind farm in Denmark, which is a farm experiencing strong horizontal wind-speed gradients because of its size and proximity to land. Mesoscale model simulations are used to study the horizontal wind-speed gradients over the wind farm. From analysis of the mesoscale simulations and supervisory control and data acquisition (SCADA, we show that for westerly flow in particular, there is a clear horizontal wind-speed gradient over the wind farm. We also use the mesoscale simulations to derive the undisturbed inflow conditions that are coupled with three commonly used wake models: two engineering approaches (the Park and G. C. Larsen models and a linearized Reynolds-averaged Navier–Stokes approach (Fuga. The effect of the horizontal wind-speed gradient on annual energy production estimates is not found to be critical compared to estimates from both the average undisturbed wind climate of all turbines' positions and the undisturbed wind climate of a position in the middle of the wind farm. However, annual energy production estimates can largely differ when using wind climates at positions that are strongly influenced by the horizontal wind-speed gradient. When looking at westerly flow wake cases, where the impact of the horizontal wind-speed gradient on the power of the undisturbed turbines is largest, the wake models agree with the SCADA fairly well; when looking at a southerly flow case, where the wake losses are highest, the wake models tend to underestimate the wake loss. With the mesoscale-wake model setup, we are also able to estimate the capacity factor of the wind farm rather well when compared to that derived from the SCADA. Finally, we estimate the uncertainty of the wake models by bootstrapping the SCADA. The models tend to underestimate the wake losses (the median relative model error is 8.75 % and the engineering wake models are as uncertain as Fuga. These results are specific for

  15. Data report: the wake of a horizontal-axis wind turbine model, measurements in uniform approach flow and in a simulated atmospheric boundary layer

    NARCIS (Netherlands)

    Talmon, A.M.

    1985-01-01

    Wake effects will cause power loss when wínd turbínes are grouped in so called wind turbine parks. Wind tunnel measurements of the wake of a wind turbíne model are conducted in order to refine calculatíons of wake effects. Wake effects caused by tower and nacelle are studied in uniform flow. Wake

  16. Anisotropy of turbulence in wind turbine wakes

    Energy Technology Data Exchange (ETDEWEB)

    Gomez-Elvira, Rafael [Comision Nacional de Energia (Spain); Crespo, Antonio; Migoya, Emilio; Manuel, Fernando [Departamento de Ingenieria Energetica y Fluidomecanica, Escuela Tecnica Superior de Ingenieros Industriales, Universidad Politecnica de Madrid, Jose Gutierrez Abascal, 2. 28006 Madrid (Spain); Hernandez, Julio [Departamento de Mecanica, ETSII, Universidad Nacional de Educacion a Distancia, Ciudad Universitaria, 28040 Madrid (Spain)

    2005-10-01

    This work is mainly dedicated to the study of non-isotropic characteristics of turbulence in wind turbine wakes, specifically the shear layer of the near wake. A calculation method based on an explicit algebraic model for the components of the turbulent stress tensor is proposed, and the results are found to be in acceptable agreement with experimental results. Analytical expressions for the estimation of an upper limit of the global turbulence kinetic energy, k, and the individual contributions of each diagonal term in the turbulent stress tensor are proposed. Their predictions are compared with experimental results.

  17. Simulation of wind turbine wakes using the actuator line technique

    Science.gov (United States)

    Sørensen, Jens N.; Mikkelsen, Robert F.; Henningson, Dan S.; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J.

    2015-01-01

    The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. PMID:25583862

  18. Wake interaction and power production of variable height model wind farms

    DEFF Research Database (Denmark)

    Vested, Malene Hovgaard; Hamilton, N.; Sørensen, Jens Nørkær

    2014-01-01

    Understanding wake dynamics is an ongoing research topic in wind energy, since wakes have considerable effects on the power production when wind turbines are placed in a wind farm. Wind tunnel experiments have been conducted to study the wake to wake interaction in a model wind farm in tandem...... with measurements of the extracted power. The aim is to investigate how alternating mast height influences the interaction of the wakes and the power production. Via the use of stereo-particle image velocimetry, the flow field was obtained in the first and last rows of the wind turbine array as a basis...... of comparison. It was found that downstream of the exit row wind turbine, the power was increased by 25% in the case of a staggered height configuration. This is partly due to the fact that the taller turbines reach into a flow area with a softened velocity gradient. Another aspect is that the wake downstream...

  19. Active Power Dispatch Method for a Wind Farm Central Controller Considering Wake Effect

    DEFF Research Database (Denmark)

    Tian, Jie; Su, Chi; N. Soltani, Mohsen

    2014-01-01

    With the increasing integration of the wind power into the power system, wind farm are required to be controlled as a single unit and have all the same control tasks as conventional power plants. The wind farm central controller receives control orders from Transmission System Operator (TSO), the...

  20. Modeling wake effects in large wind farms in complex terrain: the problem, the methods and the issues

    DEFF Research Database (Denmark)

    Politis, E.S.; Prospathopoulos, J.; Cabezon, D.

    2012-01-01

    turbulence closures, are used. The wind turbines are modeled as momentum absorbers by means of their thrust coefficient through the actuator disk approach. Alternative methods for estimating the reference wind speed in the calculation of the thrust are tested. The work presented in this paper is part......Computational fluid dynamic (CFD) methods are used in this paper to predict the power production from entire wind farms in complex terrain and to shed some light into the wake flow patterns. Two full three-dimensional Navier–Stokes solvers for incompressible fluid flow, employing k - ε and k - ω...

  1. On the Turbulent Mixing in Horizontal Axis Wind Turbine Wakes

    NARCIS (Netherlands)

    Lignarolo, L.E.M.

    2016-01-01

    The wake flow of a horizontal axis wind turbine is characterised by lower wind speed and higher turbulence than the free-stream conditions. When clustered in large wind farms, wind turbines regularly operate inside the wake of one or more upstream machines. This is a major cause of energy production

  2. Simulation of wind turbine wakes using the actuator line technique

    DEFF Research Database (Denmark)

    Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming; Henningson, Dan S.

    2015-01-01

    The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance...... predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results...... of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated...

  3. Wind Turbine Down-regulation Strategy for Minimum Wake Deficit

    DEFF Research Database (Denmark)

    Ma, Kuichao; Zhu, Jiangsheng; N. Soltani, Mohsen

    2017-01-01

    on minimum wake deficit is proposed in this paper, for the power improvement of the downwind turbine in low and medium wind speed region. The main idea is to operate turbine work at an appropriate operating point through rotor speed and torque control. The effectiveness of the strategy is verified...

  4. PIV in a model wind turbine rotor wake

    DEFF Research Database (Denmark)

    Meyer, Knud Erik; Naumov, Igor; Karbadin, Ivan

    2013-01-01

    Stereoscopic particle image velocimetry (PIV) measurements of the flow in the wake of scale model of a horizontal axis wind turbine is presented Near the rotor, measurements are made in vertical planes intersecting the rotor axis These planes capture flow effect from the tip and root vortices...

  5. A stochastic wind turbine wake model based on new metrics for wake characterization: A stochastic wind turbine wake model based on new metrics for wake characterization

    Energy Technology Data Exchange (ETDEWEB)

    Doubrawa, Paula [Sibley School of Mechanical and Aerospace Engineering, Cornell University, Upson Hall Ithaca 14850 New York USA; Barthelmie, Rebecca J. [Sibley School of Mechanical and Aerospace Engineering, Cornell University, Upson Hall Ithaca 14850 New York USA; Wang, Hui [Sibley School of Mechanical and Aerospace Engineering, Cornell University, Upson Hall Ithaca 14850 New York USA; Churchfield, Matthew J. [National Renewable Energy Laboratory, Golden 80401 Colorado USA

    2016-08-04

    Understanding the detailed dynamics of wind turbine wakes is critical to predicting the performance and maximizing the efficiency of wind farms. This knowledge requires atmospheric data at a high spatial and temporal resolution, which are not easily obtained from direct measurements. Therefore, research is often based on numerical models, which vary in fidelity and computational cost. The simplest models produce axisymmetric wakes and are only valid beyond the near wake. Higher-fidelity results can be obtained by solving the filtered Navier-Stokes equations at a resolution that is sufficient to resolve the relevant turbulence scales. This work addresses the gap between these two extremes by proposing a stochastic model that produces an unsteady asymmetric wake. The model is developed based on a large-eddy simulation (LES) of an offshore wind farm. Because there are several ways of characterizing wakes, the first part of this work explores different approaches to defining global wake characteristics. From these, a model is developed that captures essential features of a LES-generated wake at a small fraction of the cost. The synthetic wake successfully reproduces the mean characteristics of the original LES wake, including its area and stretching patterns, and statistics of the mean azimuthal radius. The mean and standard deviation of the wake width and height are also reproduced. This preliminary study focuses on reproducing the wake shape, while future work will incorporate velocity deficit and meandering, as well as different stability scenarios.

  6. Analysis of turbulent wake behind a wind turbine

    DEFF Research Database (Denmark)

    Kermani, Nasrin Arjomand; Andersen, Søren Juhl; Sørensen, Jens Nørkær

    2013-01-01

    The aim of this study is to improve the classical analytical model for estimation of the rate of wake expansion and the decay of wake velocity deficit in the far wake region behind a wind turbine. The relations for a fully turbulent axisymmetric far wake were derived by applying the mass and mome......The aim of this study is to improve the classical analytical model for estimation of the rate of wake expansion and the decay of wake velocity deficit in the far wake region behind a wind turbine. The relations for a fully turbulent axisymmetric far wake were derived by applying the mass...... ambient wind velocities (higher thrust coefficients), this trend may be improved due to the faster recovery of the wake and therefore closer values to the theoretical approach may be obtained. In addition, the assumption of self-similarity behavior of the mean velocity profile, when scaled with center...

  7. Engineering models for merging wakes in wind farm optimization applications

    DEFF Research Database (Denmark)

    Machefaux, Ewan; Larsen, Gunner Chr.; Murcia Leon, Juan Pablo

    2015-01-01

    The present paper deals with validation of 4 different engineering wake superposition approaches against detailed CFD simulations and covering different turbine interspacing, ambient turbulence intensities and mean wind speeds. The first engineering model is a simple linear superposition of wake ...

  8. Description of signature scales in a floating wind turbine model wake subjected to varying turbulence intensity

    Science.gov (United States)

    Kadum, Hawwa; Rockel, Stanislav; Holling, Michael; Peinke, Joachim; Cal, Raul Bayon

    2017-11-01

    The wake behind a floating model horizontal axis wind turbine during pitch motion is investigated and compared to a fixed wind turbine wake. An experiment is conducted in an acoustic wind tunnel where hot-wire data are acquired at five downstream locations. At each downstream location, a rake of 16 hot-wires was used with placement of the probes increasing radially in the vertical, horizontal, and diagonally at 45 deg. In addition, the effect of turbulence intensity on the floating wake is examined by subjecting the wind turbine to different inflow conditions controlled through three settings in the wind tunnel grid, a passive and two active protocols, thus varying in intensity. The wakes are inspected by statistics of the point measurements, where the various length/time scales are considered. The wake characteristics for a floating wind turbine are compared to a fixed turbine, and uncovering its features; relevant as the demand for exploiting deep waters in wind energy is increasing.

  9. Volumetric LiDAR scanning of a wind turbine wake and comparison with a 3D analytical wake model

    Science.gov (United States)

    Carbajo Fuertes, Fernando; Porté-Agel, Fernando

    2016-04-01

    A correct estimation of the future power production is of capital importance whenever the feasibility of a future wind farm is being studied. This power estimation relies mostly on three aspects: (1) a reliable measurement of the wind resource in the area, (2) a well-established power curve of the future wind turbines and, (3) an accurate characterization of the wake effects; the latter being arguably the most challenging one due to the complexity of the phenomenon and the lack of extensive full-scale data sets that could be used to validate analytical or numerical models. The current project addresses the problem of obtaining a volumetric description of a full-scale wake of a 2MW wind turbine in terms of velocity deficit and turbulence intensity using three scanning wind LiDARs and two sonic anemometers. The characterization of the upstream flow conditions is done by one scanning LiDAR and two sonic anemometers, which have been used to calculate incoming vertical profiles of horizontal wind speed, wind direction and an approximation to turbulence intensity, as well as the thermal stability of the atmospheric boundary layer. The characterization of the wake is done by two scanning LiDARs working simultaneously and pointing downstream from the base of the wind turbine. The direct LiDAR measurements in terms of radial wind speed can be corrected using the upstream conditions in order to provide good estimations of the horizontal wind speed at any point downstream of the wind turbine. All this data combined allow for the volumetric reconstruction of the wake in terms of velocity deficit as well as turbulence intensity. Finally, the predictions of a 3D analytical model [1] are compared to the 3D LiDAR measurements of the wind turbine. The model is derived by applying the laws of conservation of mass and momentum and assuming a Gaussian distribution for the velocity deficit in the wake. This model has already been validated using high resolution wind-tunnel measurements

  10. Development and validation of a new two-dimensional wake model for wind turbine wakes

    DEFF Research Database (Denmark)

    Tian, Linlin; Zhu, Wei Jun; Shen, Wen Zhong

    2015-01-01

    , wind tunnel experiments, and results of an advanced k-ω turbulence model as well as large eddy simulations. From the comparisons, it is found that the proposed new wake model gives a good prediction in terms of both shape and velocity amplitude of the wake deficit, especially in the far wake which......A new two-dimensional (2D) wake model is developed and validated in this article to predict the velocity and turbulence distribution in the wake of a wind turbine. Based on the classical Jensen wake model, this model is further employing a cosine shape function to redistribute the spread...... of the wake deficit in the crosswind direction. Moreover, a variable wake decay rate is proposed to take into account both the ambient turbulence and the rotor generated turbulence, different from a constant wake decay rate used in the Jensen model. The obtained results are compared to field measurements...

  11. Comparing satellite SAR and wind farm wake models

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Vincent, P.; Husson, R.

    2015-01-01

    . These extend several tens of kilometres downwind e.g. 70 km. Other SAR wind maps show near-field fine scale details of wake behind rows of turbines. The satellite SAR wind farm wake cases are modelled by different wind farm wake models including the PARK microscale model, the Weather Research and Forecasting...... (WRF) model in high resolution and WRF with coupled microscale parametrization....

  12. Modelling and Measuring Flow and Wind Turbine Wakes in Large Wind Farms Offshore

    DEFF Research Database (Denmark)

    Barthelmie, Rebecca Jane; Hansen, Kurt Schaldemose; Frandsen, Sten Tronæs

    2009-01-01

    Average power losses due to wind turbine wakes are of the order of 10 to 20% of total power output in large offshore wind farms. Accurately quantifying power losses due to wakes is, therefore, an important part of overall wind farm economics. The focus of this research is to compare different types...... power losses due to wakes and loads. The research presented is part of the EC-funded UpWind project, which aims to radically improve wind turbine and wind farm models in order to continue to improve the costs of wind energy. Reducing wake losses, or even reduce uncertainties in predicting power losses...... from wakes, contributes to the overall goal of reduced costs. Here, we assess the state of the art in wake and flow modelling for offshore wind forms, the focus so for has been cases at the Horns Rev wind form, which indicate that wind form models require modification to reduce under-prediction of wake...

  13. Why the Coriolis force turns a wind farm wake clockwise in the Northern Hemisphere

    DEFF Research Database (Denmark)

    van der Laan, Paul; Sørensen, Niels N.

    2017-01-01

    and a roughness change. When the wind farm simulations are performed with a horizontally constant Coriolis force in order to isolate the effect of the wind veer, the wind farm wake deflection of the 5 × 5 actuator disks simulation remains unchanged. This proves that the present wind veer deflects the wind farm......The interaction between the Coriolis force and a wind farm wake is investigated by Reynoldsaveraged Navier–Stokes simulations, using two different wind farm representations: a high roughness and 5 × 5 actuator disks. Surprisingly, the calculated wind farm wake deflection is the opposite in the two...... simulations. A momentum balance in the cross flow direction shows that the interaction between the Coriolis force and the 5 × 5 actuator disks is complex due to turbulent mixing of veered momentum from above into the wind farm, which is not observed for the interaction between the Coriolis force...

  14. Why the Coriolis force turns a wind farm wake clockwise in the Northern Hemisphere

    Directory of Open Access Journals (Sweden)

    M. P. van der Laan

    2017-05-01

    Full Text Available The interaction between the Coriolis force and a wind farm wake is investigated by Reynolds-averaged Navier–Stokes simulations, using two different wind farm representations: a high roughness and 5 × 5 actuator disks. Surprisingly, the calculated wind farm wake deflection is the opposite in the two simulations. A momentum balance in the cross flow direction shows that the interaction between the Coriolis force and the 5 × 5 actuator disks is complex due to turbulent mixing of veered momentum from above into the wind farm, which is not observed for the interaction between the Coriolis force and a roughness change. When the wind farm simulations are performed with a horizontally constant Coriolis force in order to isolate the effect of the wind veer, the wind farm wake deflection of the 5 × 5 actuator disks simulation remains unchanged. This proves that the present wind veer deflects the wind farm wake and not the local changes in the Coriolis force in the wake deficit region. An additional simulation of a single actuator disk, operating in a shallow atmospheric boundary layer, confirms that the Coriolis force indirectly turns a wind turbine wake clockwise, as observed from above, due to the presence of a strong wind veer.

  15. Coordinated Power Dispatch of a PMSG based Wind Farm for Output Power Maximizing Considering the Wake Effect and Losses

    DEFF Research Database (Denmark)

    Zhang, Baohua; Hu, Weihao; Hou, Peng

    2016-01-01

    active power and reactive power dispatch strategy is proposed for a Permanent magnet synchronous generator (PMSG) based WF, in order to maximize the total output power by reducing the wake effect and losses inside the devices of the WF, including the copper loss and iron loss of PMSGs, losses inside...

  16. On the spread and decay of wind turbine wakes in ambient turbulence

    Science.gov (United States)

    Johnson, P. B.; Jonsson, C.; Achilleos, S.; Eames, I.

    2014-12-01

    The decay of the downstream wake of a wind turbine plays an important role in the performance of wind farms. The spread and decay of a wake depend both on wake meandering (advection of the wake as a whole) and wake diffusion (widening of the wake within its meandering frame of reference). Both of these effects depend strongly on the intensity of the ambient turbulence relative to the velocity deficit in the wake, and on the integral length scale of the turbulence relative to the wake width. Recent theory, which we review here, shows how intense large-scale turbulence can lead to a rapid x-2 decay in the time-averaged centreline velocity deficit, as compared to a x-1 decay for smaller scale turbulence, where x is distance downstream. We emphasise in this paper that common wind farm models do not predict this rapid decay. We present new experimental measurements of the velocity deficit downstream of a porous disc in relatively large-scale ambient turbulence which corroborate predictions of a x-2 decay, and we show theoretically that the commonly used k-epsilon model does not capture this effect. We further show that a commercial CFD package, configured to match our experiments and employing the k-epsilon model, fails to predict such rapid decay. We conclude that steady simulations of wind turbine wake dynamics are insufficient for informing wind farm layout optimisation.

  17. On the spread and decay of wind turbine wakes in ambient turbulence

    International Nuclear Information System (INIS)

    Johnson, P B; Jonsson, C; Achilleos, S; Eames, I

    2014-01-01

    The decay of the downstream wake of a wind turbine plays an important role in the performance of wind farms. The spread and decay of a wake depend both on wake meandering (advection of the wake as a whole) and wake diffusion (widening of the wake within its meandering frame of reference). Both of these effects depend strongly on the intensity of the ambient turbulence relative to the velocity deficit in the wake, and on the integral length scale of the turbulence relative to the wake width. Recent theory, which we review here, shows how intense large-scale turbulence can lead to a rapid x −2 decay in the time-averaged centreline velocity deficit, as compared to a x −1 decay for smaller scale turbulence, where x is distance downstream. We emphasise in this paper that common wind farm models do not predict this rapid decay. We present new experimental measurements of the velocity deficit downstream of a porous disc in relatively large-scale ambient turbulence which corroborate predictions of a x −2 decay, and we show theoretically that the commonly used k-ε model does not capture this effect. We further show that a commercial CFD package, configured to match our experiments and employing the k-ε model, fails to predict such rapid decay. We conclude that steady simulations of wind turbine wake dynamics are insufficient for informing wind farm layout optimisation

  18. Simulation of wind turbine wakes using the actuator line technique.

    Science.gov (United States)

    Sørensen, Jens N; Mikkelsen, Robert F; Henningson, Dan S; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J

    2015-02-28

    The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  19. Application of engineering models to predict wake deflection due to a tilted wind turbine

    DEFF Research Database (Denmark)

    Guntur, Srinivas; Troldborg, Niels; Gaunaa, Mac

    2012-01-01

    such a mechanism introduces control complications due to changing wind directions. Deflecting the wake in the vertical direction using tilt, on the other hand, overcomes this challenge. In this paper, the feasibility of steering wake is explored in a simple uniform inflow case. This is done by trying to model......It is a known fact that the power produced by wind turbines operating inside an array decreases due to the wake effects of the upstream turbines. It has been proposed previously to use the yaw mechanism as a potential means to steer the upstream wake away from downstream turbines, however...

  20. Accurate wind farm development and operation. Advanced wake modelling

    Energy Technology Data Exchange (ETDEWEB)

    Brand, A.; Bot, E.; Ozdemir, H. [ECN Unit Wind Energy, P.O. Box 1, NL 1755 ZG Petten (Netherlands); Steinfeld, G.; Drueke, S.; Schmidt, M. [ForWind, Center for Wind Energy Research, Carl von Ossietzky Universitaet Oldenburg, D-26129 Oldenburg (Germany); Mittelmeier, N. REpower Systems SE, D-22297 Hamburg (Germany))

    2013-11-15

    The ability is demonstrated to calculate wind farm wakes on the basis of ambient conditions that were calculated with an atmospheric model. Specifically, comparisons are described between predicted and observed ambient conditions, and between power predictions from three wind farm wake models and power measurements, for a single and a double wake situation. The comparisons are based on performance indicators and test criteria, with the objective to determine the percentage of predictions that fall within a given range about the observed value. The Alpha Ventus site is considered, which consists of a wind farm with the same name and the met mast FINO1. Data from the 6 REpower wind turbines and the FINO1 met mast were employed. The atmospheric model WRF predicted the ambient conditions at the location and the measurement heights of the FINO1 mast. May the predictability of the wind speed and the wind direction be reasonable if sufficiently sized tolerances are employed, it is fairly impossible to predict the ambient turbulence intensity and vertical shear. Three wind farm wake models predicted the individual turbine powers: FLaP-Jensen and FLaP-Ainslie from ForWind Oldenburg, and FarmFlow from ECN. The reliabilities of the FLaP-Ainslie and the FarmFlow wind farm wake models are of equal order, and higher than FLaP-Jensen. Any difference between the predictions from these models is most clear in the double wake situation. Here FarmFlow slightly outperforms FLaP-Ainslie.

  1. Wake interaction and power production of variable height model wind farms

    International Nuclear Information System (INIS)

    Vested, M H; Sørensen, J N; Hamilton, N; Cal, R B

    2014-01-01

    Understanding wake dynamics is an ongoing research topic in wind energy, since wakes have considerable effects on the power production when wind turbines are placed in a wind farm. Wind tunnel experiments have been conducted to study the wake to wake interaction in a model wind farm in tandem with measurements of the extracted power. The aim is to investigate how alternating mast height influences the interaction of the wakes and the power production. Via the use of stereo-particle image velocimetry, the flow field was obtained in the first and last rows of the wind turbine array as a basis of comparison. It was found that downstream of the exit row wind turbine, the power was increased by 25% in the case of a staggered height configuration. This is partly due to the fact that the taller turbines reach into a flow area with a softened velocity gradient. Another aspect is that the wake downstream of a tall wind turbine to some extent passes above the standard height wind turbine. Overall the experiments show that the velocity field downstream of the exit row changes considerably when the mast height is alternating

  2. Wake characteristics of wind turbines in utility-scale wind farms

    Science.gov (United States)

    Yang, Xiaolei; Foti, Daniel; Sotiropoulos, Fotis

    2017-11-01

    The dynamics of turbine wakes is affected by turbine operating conditions, ambient atmospheric turbulent flows, and wakes from upwind turbines. Investigations of the wake from a single turbine have been extensively carried out in the literature. Studies on the wake dynamics in utility-scale wind farms are relatively limited. In this work, we employ large-eddy simulation with an actuator surface or actuator line model for turbine blades to investigate the wake dynamics in utility-scale wind farms. Simulations of three wind farms, i.e., the Horns Rev wind farm in Denmark, Pleasant Valley wind farm in Minnesota, and the Vantage wind farm in Washington are carried out. The computed power shows a good agreement with measurements. Analysis of the wake dynamics in the three wind farms is underway and will be presented in the conference. This work was support by Xcel Energy (RD4-13). The computational resources were provided by National Renewable Energy Laboratory.

  3. Results of Sexbierum Wind Farm: single wake measurements

    NARCIS (Netherlands)

    Cleijne, J.W.

    1993-01-01

    In the framework of the JOULE-0064 'Full-scale Measurements in Wind Turbine Arrays' in the period between June-November 1992 measurements have been performed in the Sexbierum Wind Farm. The aim of the measurements is to provide data for the validation of wake and wind farm models, which are being

  4. Wake models developed during the Wind Shadow Project

    DEFF Research Database (Denmark)

    Larsen, Søren Ejling; Ott, Søren; Pena Diaz, Alfredo

    The Wind Shadow project has developed and validated improved models for determining the wakes losses, and thereby the array efficiency of very large, closely packed wind farms. The rationale behind the project has been that the existing software has been covering these types of wind farms poorly...

  5. Influence of the Coriolis force on the structure and evolution of wind turbine wakes

    Science.gov (United States)

    Abkar, Mahdi; Porté-Agel, Fernando

    2016-10-01

    In this study, large-eddy simulation combined with a turbine model is used to investigate the effect of vertical wind veer associated with the Coriolis force on the structure and evolution of wind turbine wakes. In order to isolate the Coriolis effect on the wake, two cases are considered. In the first case, atmospheric boundary-layer flow is driven by a geostrophic wind, including the effect of Earth's rotation and the Coriolis force. In the second case, the boundary-layer flow is unidirectional and is forced by an imposed pressure gradient. Both cases have the same mean horizontal velocity and turbulence intensity at the hub height. The simulation results show that the Coriolis force significantly affects the aerodynamics of the wake including the mean velocity deficit, turbulence statistics, and wake-meandering characteristics downwind of the turbine. In particular, when the flow is forced by a geostrophic wind, vertical wind veer causes a skewed spatial structure in the wake. Moreover, the presence of lateral wind shear, in addition to the vertical one, enhances the shear production of turbulent kinetic energy and the turbulent momentum flux. This leads to a larger flow entrainment and, thus, a faster wake recovery compared to the case forced by unidirectional pressure gradient. Consistent with this result, wake meandering is also stronger in both lateral and vertical directions in the case of geostrophic forcing compared to the case with pressure-gradient forcing.

  6. Wake models developed during the Wind Shadow project

    Energy Technology Data Exchange (ETDEWEB)

    Larsen, S.; Ott, S.; Pena, A.; Berg, J.; Nielsen, M.; Rathmann, O.; Joergensen, H.

    2011-11-15

    The Wind Shadow project has developed and validated improved models for determining the wakes losses, and thereby the array efficiency of very large, closely packed wind farms. The rationale behind the project has been that the existing software has been covering these types of wind farms poorly, both with respect to the densely packed turbines and the large fetches needed to describe the collective shadow effects of one farm to the next. Further the project has developed the necessary software for the use of the models. Guidelines with recommendations for the use of the models are included in the model deliverables. The project has been carried out as a collaborative project between Risoe DTU, DONG, Vattenfall, DNV and VESTAS, and it has been financed by energinet.dk grant no. 10086. (Author)

  7. Automatic tracking of wake vortices using ground-wind sensor data

    Science.gov (United States)

    1977-01-03

    Algorithms for automatic tracking of wake vortices using ground-wind anemometer : data are developed. Methods of bad-data suppression, track initiation, and : track termination are included. An effective sensor-failure detection-and identification : ...

  8. A CFD model of the wake of an offshore wind farm: using a prescribed wake inflow

    International Nuclear Information System (INIS)

    Rethore, P-E; Bechmann, A; Soerensen, N N; Frandsen, S T; Mann, J; Joergensen, H E; Rathmann, O; Larsen, S E

    2007-01-01

    An CFD model of the wake of an offshore wind farm, expanding existing measurements is proposed. The method is based on solving the Navier Stokes equation in a large domain downstream an offshore wind farm. The inflow of the domain is estimated using existing met mast measurements from both free stream and directly in-wake conditions. A comparison between the simulation results and measurements from a met mast are presented and the shortcomings of the methods are discussed

  9. Modelling of offshore wind turbine wakes with the wind farm program FLaP

    DEFF Research Database (Denmark)

    Lange, B.; Waldl, H.P.; Guerrero, A.G.

    2003-01-01

    The wind farm layout program FLaP estimates the wind speed at any point in a wind farm and the power output of the turbines. The ambient flow conditions and the properties of the turbines and the farm are used as input. The core of the program is an axisymmetric wake model describing the wake...

  10. Nonlinear Eddy Viscosity Models applied to Wind Turbine Wakes

    DEFF Research Database (Denmark)

    Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan

    2013-01-01

    The linear k−ε eddy viscosity model and modified versions of two existing nonlinear eddy viscosity models are applied to single wind turbine wake simulations using a Reynolds Averaged Navier-Stokes code. Results are compared with field wake measurements. The nonlinear models give better results...

  11. Wind Farm Wake: The 2016 Horns Rev Photo Case

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Nygaard, Nicolai Gayle; Volker, Patrick

    2017-01-01

    are that a humid and warm air mass was advected from the southwest over cold sea and the dew-point temperature was such that cold-water advection fog formed in a shallow layer. The flow was stably stratified and the freestream wind speed was 13 m/s at hub height, which means that most turbines produced at or near...... rated power. The wind direction was southwesterly and long, narrow wakes persisted several rotor diameters downwind of the wind turbines. Eventually mixing of warm air from aloft dispersed the fog in the far wake region of the wind farm....

  12. Large Eddy Simulation of Vertical Axis Wind Turbine Wakes

    Directory of Open Access Journals (Sweden)

    Sina Shamsoddin

    2014-02-01

    Full Text Available In this study, large eddy simulation (LES is combined with a turbine model to investigate the wake behind a vertical-axis wind turbine (VAWT in a three-dimensional turbulent flow. Two methods are used to model the subgrid-scale (SGS stresses: (a the Smagorinsky model; and (b the modulated gradient model. To parameterize the effects of the VAWT on the flow, two VAWT models are developed: (a the actuator swept-surface model (ASSM, in which the time-averaged turbine-induced forces are distributed on a surface swept by the turbine blades, i.e., the actuator swept surface; and (b the actuator line model (ALM, in which the instantaneous blade forces are only spatially distributed on lines representing the blades, i.e., the actuator lines. This is the first time that LES has been applied and validated for the simulation of VAWT wakes by using either the ASSM or the ALM techniques. In both models, blade-element theory is used to calculate the lift and drag forces on the blades. The results are compared with flow measurements in the wake of a model straight-bladed VAWT, carried out in the Institute de Méchanique et Statistique de la Turbulence (IMST water channel. Different combinations of SGS models with VAWT models are studied, and a fairly good overall agreement between simulation results and measurement data is observed. In general, the ALM is found to better capture the unsteady-periodic nature of the wake and shows a better agreement with the experimental data compared with the ASSM. The modulated gradient model is also found to be a more reliable SGS stress modeling technique, compared with the Smagorinsky model, and it yields reasonable predictions of the mean flow and turbulence characteristics of a VAWT wake using its theoretically-determined model coefficient.

  13. Drone Based Experimental Investigation of Wind Turbine Wake Evolution

    Science.gov (United States)

    Subramanian, Balaji, , Dr.; Chokani, Ndaona, , Dr.; Abhari, Reza, Prof. _., Dr.

    2016-11-01

    The characteristics of the wake downstream of a wind turbine has an important bearing on the optimized micrositing of wind turbines in a given land area, as well as on the loads seen by downstream turbines. We use a novel measurement system to measure the flow field upstream and in the wake of a full-scale wind turbine. The system consists of a fast response aerodynamic probe, mounted on an autonomous drone that is equipped with a suite of sensors. These measurements detail, for the first time at full-scale Reynolds number conditions, the evolution and breakdown of tip vortices that are characteristic of the near wake, as well as the turbulent mixing and entrainment of more energised flow, which are distinctive in the far wake. A short-time Fourier transform (STFT) analysis method is used to derive time-localized TKE along the drone's trajectory. Detailed upstream and wake measurements are needed to understand the flow behavior, as it helps in developing and validating simplified wake models that can approximate the wake qualities. Comparisons of these measurements to recently developed wake prediction models highlights how these measurements can support further model development.

  14. Validation of the dynamic wake meander model for loads and power production in the Egmond aan Zee wind farm

    DEFF Research Database (Denmark)

    Larsen, Torben J.; Aagaard Madsen, Helge; Larsen, Gunner Chr.

    2013-01-01

    is excellent regarding power production in both free and wake sector, and a very good agreement is seen for the load comparisons too. This enables the conclusion that wake meandering, caused by large scale ambient turbulence, is indeed an important contribution to wake loading in wind farms. Copyright © 2012......This paper investigates wake effects on load and power production by using the dynamic wake meander (DWM) model implemented in the aeroelastic code HAWC2. The instationary wind farm flow characteristics are modeled by treating the wind turbine wakes as passive tracers transported downstream using...... a meandering process driven by the low frequent cross-wind turbulence components. The model complex is validated by comparing simulated and measured loads for the Dutch Egmond aan Zee wind farm consisting of 36 Vestas V90 turbine located outside the coast of the Netherlands. Loads and production are compared...

  15. Wind Farm Wake: The 2016 Horns Rev Photo Case

    Directory of Open Access Journals (Sweden)

    Charlotte Bay Hasager

    2017-03-01

    Full Text Available Offshore wind farm wakes were observed and photographed in foggy conditions at Horns Rev 2 on 25 January 2016 at 12:45 UTC. These new images show highly contrasting conditions regarding the wind speed, turbulence intensity, atmospheric stability, weather conditions and wind farm wake development as compared to the Horns Rev 1 photographs from 12 February 2008. The paper examines the atmospheric conditions from satellite images, radiosondes, lidar and wind turbine data and compares the observations to results from atmospheric meso-scale modelling and large eddy simulation. Key findings are that a humid and warm air mass was advected from the southwest over cold sea and the dew-point temperature was such that cold-water advection fog formed in a shallow layer. The flow was stably stratified and the freestream wind speed was 13 m/s at hub height, which means that most turbines produced at or near rated power. The wind direction was southwesterly and long, narrow wakes persisted several rotor diameters downwind of the wind turbines. Eventually mixing of warm air from aloft dispersed the fog in the far wake region of the wind farm.

  16. Modelling and measurements of wakes in large wind farms

    DEFF Research Database (Denmark)

    Barthelmie, Rebecca Jane; Rathmann, Ole; Frandsen, Sten Tronæs

    2007-01-01

    The paper presents research conducted in the Flow workpackage of the EU funded UPWIND project which focuses on improving models of flow within and downwind of large wind farms in complex terrain and offshore. The main activity is modelling the behaviour of wind turbine wakes in order to improve p...

  17. Field investigation of a wake structure downwind of a VANT (Vertical-Axis Wind Turbine) in a wind farm array

    Science.gov (United States)

    Liu, H. T.; Buck, J. W.; Germain, A. C.; Hinchee, M. E.; Solt, T. S.; Leroy, G. M.; Srnsky, R. A.

    1988-09-01

    The effects of upwind turbine wakes on the performance of a FloWind 17-m vertical-axis wind turbine (VAWT) were investigated through a series of field experiments conducted at the FloWind wind farm on Cameron Ridge, Tehachapi, California. From the field measurements, we derived the velocity and power/energy deficits under various turbine on/off configurations. Much information was provided to characterize the structure of VAWT wakes and to assess their effects on the performance of downwind turbines. A method to estimate the energy deficit was developed based on the measured power deficit and the wind speed distributions. This method may be adopted for other turbine types and sites. Recommendations are made for optimizing wind farm design and operations, as well as for wind energy management.

  18. Actuator Line Modeling of Wind Turbine Wakes

    DEFF Research Database (Denmark)

    Troldborg, Niels

    2009-01-01

    with the 3D Navier Stokes solver EllipSys3D and a LES turbulence model. Simple models, based on applying body forces in the computational domain, are developed for imposing sheared and turbulent infow and their validity is discussed. A few computations on stand alone turbines are compared to measurements...... inflow shows that besides an expected vertical skewed wake the wake also becomes increasingly asymmetric in the horizontal direction as it is convected downstream. The latter phenomena, which is also often observed in measurements, is argued to be caused by the rotation of the wake. A detailed study...

  19. Horns Rev 2 offshore wind farm photo case with wakes observed in 2016

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Nygaard, Nicolai Gayle; Volker, Patrick

    results from atmospheric WRF meso-scale modelling, Park wake model and large eddy simulation wake model are prepared and analysed. At the time of the photos a humid and warm air mass was advected from the southwest over cold sea. The dew-point temperature was such that cold-water advection fog formed...... air from aloft dispersed the fog. This is noted in the photos and WRF model results. The physical processes are modelled from WRF without and with a parametrization for the wind farm included. The results indicate a difference in liquid water content showing that a drying effect appear downwind...... a temperature scheme, and the results indicate the pattern of fog in the wake. Due to stable stratification the wakes are long and narrow with a smooth appearance. The LES results are novel and for the first time ever compared to visually observed fog cones. In the far-field of the wind farm wake mixing of warm...

  20. Gap Winds and Wakes: SAR Observations and Numerical Simulations.

    Science.gov (United States)

    Pan, Feifei; Smith, Ronald B.

    1999-04-01

    The nature of terrain-induced gap winds and wakes in the atmosphere is examined using surface wind data from synthetic aperture radar (SAR) and the shallow water equations. The shallow water model is used to predict the types of wake-jet wind patterns that might occur behind an idealized pair of bell-shaped hills with a gap between them. A regime diagram is constructed based on the width of the gap and the upstream Froude number. Specific predictions of the model are found to compare moderately well with SAR data from four examples of airflow near Unimak Island in the Aleutian Chain. The model predicts the observed wakes and jets, including jets that exceed the upstream speed. Theoretical analysis considers the relative importance of rising terrain and narrowing valley walls in the acceleration of gap winds. Wind speeds in the wake region are controlled by the Bernoulli function and regional pressure. Gap winds therefore are streams of air that have avoided Bernoulli loss over the terrain by passing through gaps. The speed of gap winds can exceed the upstream speed only in ridgelike situations when the regional leeside pressure is lower than the upstream pressure.

  1. Study on the Wake of a Miniature Wind Turbine Using the Reynolds Stress Model

    Directory of Open Access Journals (Sweden)

    Jianxiao Hu

    2016-09-01

    Full Text Available The Reynolds Stress Model (RSM is adopted to simulate the wind turbine wake and the simulation results are compared with the wind tunnel test data, simulation results from the standard k-ε model and a modified k-ε model. RSM shows good performance in predicting the turbine wakes velocity, turbulence intensity and the kinetic shear stress, while the k-ε based models fail to predict either wakes velocity or turbulence intensity. Simulation results show that the wake velocity will be recovered up to 90% at around 10 D downstream of the turbine (D denotes turbine rotor diameter and it stops at 91% at around 16 D downstream. The wake turbulence intensity reaches a maximum at around 5 D downstream of turbine. Further investigation shows that the horizontal profile of the wakes velocity can be approximated by a Gaussian distribution, and the turbulence intensity can be approximated by a bimodal distribution. The influence of the wakes effect is limited to within ±D in the across-wind direction. The turbine wakes show clear anisotropy, which could explain the incorrect estimation on the turbulence intensity with the extended k-ε model.

  2. Experimental Study on the Wake Meandering Within a Scale Model Wind Farm Subject to a Wind-Tunnel Flow Simulating an Atmospheric Boundary Layer

    Science.gov (United States)

    Coudou, Nicolas; Buckingham, Sophia; Bricteux, Laurent; van Beeck, Jeroen

    2018-04-01

    The phenomenon of meandering of the wind-turbine wake comprises the motion of the wake as a whole in both horizontal and vertical directions as it is advected downstream. The oscillatory motion of the wake is a crucial factor in wind farms, because it increases the fatigue loads, and, in particular, the yaw loads on downstream turbines. To address this phenomenon, experimental investigations are carried out in a wind-tunnel flow simulating an atmospheric boundary layer with the Coriolis effect neglected. A 3 × 3 scaled wind farm composed of three-bladed rotating wind-turbine models is subject to a neutral boundary layer over a slightly-rough surface, i.e. corresponding to offshore conditions. Particle-image-velocimetry measurements are performed in a horizontal plane at hub height in the wakes of the three wind turbines occupying the wind-farm centreline. These measurements allow determination of the wake centrelines, with spectral analysis indicating the characteristic wavelength of the wake-meandering phenomenon. In addition, measurements with hot-wire anemometry are performed along a vertical line in the wakes of the same wind turbines, with both techniques revealing the presence of wake meandering behind all three turbines. The spectral analysis performed with the spatial and temporal signals obtained from these two measurement techniques indicates a Strouhal number of ≈ 0.20 - 0.22 based on the characteristic wake-meandering frequency, the rotor diameter and the flow speed at hub height.

  3. High resolution wind turbine wake measurements with a scanning lidar

    Science.gov (United States)

    Herges, T. G.; Maniaci, D. C.; Naughton, B. T.; Mikkelsen, T.; Sjöholm, M.

    2017-05-01

    High-resolution lidar wake measurements are part of an ongoing field campaign being conducted at the Scaled Wind Farm Technology facility by Sandia National Laboratories and the National Renewable Energy Laboratory using a customized scanning lidar from the Technical University of Denmark. One of the primary objectives is to collect experimental data to improve the predictive capability of wind plant computational models to represent the response of the turbine wake to varying inflow conditions and turbine operating states. The present work summarizes the experimental setup and illustrates several wake measurement example cases. The cases focus on demonstrating the impact of the atmospheric conditions on the wake shape and position, and exhibit a sample of the data that has been made public through the Department of Energy Atmosphere to Electrons Data Archive and Portal.

  4. Influence of Coriolis forces on the structure and evolution of wind-turbine wakes

    Science.gov (United States)

    Abkar, Mahdi; Porté-Agel, Fernando

    2015-11-01

    In this study, large-eddy simulation (LES) is combined with a turbine model to investigate the effect of Coriolis forces on the structure and evolution of wind-turbine wakes. In order to isolate the Coriolis effect on the turbulent wake flow, two set of simulations are performed. In the first set of simulations, atmospheric boundary layer (ABL) flow is driven by the geostrophic forces including the effect of Earth's rotation, while in the second case, the ABL flow is driven by a unidirectional pressure gradient forcing. Both cases have the same mean horizontal velocity and turbulence intensity at the hub height. The simulation results show that the Coriolis forces significantly affect the spatial distribution of the mean velocity deficit and turbulence statistics in the wake region. In particular, it is found that the Coriolis effect, responsible for vertical wind veer, has important lateral wake stretching effects, which in turn significantly impacts the wake recovery and wake meandering characteristics downwind of the turbines. We also apply the proper orthogonal decomposition (POD) to LES data of the wake. The results indicate a very high correlation between the most energetic modes and both maximum velocity deficit and wake meandering characteristics.

  5. Determination of wind-turbine-wake centerline for the analysis of the wake-meandering phenomenon

    Science.gov (United States)

    Coudou, Nicolas; Chatelain, Philippe; van Beeck, Jeroen; Bricteux, Laurent

    2017-11-01

    The oscillatory motion of wind turbine wakes, also known as wake meandering, is crucial in wind farms as it increases unsteady loading, in particular yawing moments, on downstream turbines. The study of this phenomenon requires, as a first step, the determination of the position of the wake. Therefore, the aim of this work is to compare different techniques to detect the wake centerline based on the velocity/momentum deficit inside the wake or on the estimation of azimuthal vorticity centroids. These techniques are applied to the data obtained from Large-Eddy simulations of the NREL 5-MW wind turbine. The computations were performed with a vortex-particle mesh code with the wind turbine rotor modeled by means of immersed lifting lines. This study constitutes a first step towards the understanding of meandering mechanisms and its accurate operational modeling. Nicolas Coudou is funded by the ``Fonds pour la Formation - la Recherche dans l'Industrie et dans l'Agriculture'' (FRIA), Belgium.

  6. Wind turbine wake stability investigations using a vortex ring modelling approach

    International Nuclear Information System (INIS)

    Baldacchino, Daniel; Van Bussel, Gerard J W

    2014-01-01

    In the present study, a simple inviscid vortex ring (VR) modelling approach is used to represent the developing rotor wake. This allows a straightforward investigation and comparison of the impact of uniform, yawed and sheared flow conditions on the development of the rotor wake, with the additional possibility of including ground effect. The effect of instabilities on the development of the wake is manually introduced in the form of perturbations of strength, ring position and size. The phenomenon of vortex filament interaction or leapfrogging, could play a role in the observation of unsteady phenomena and is therefore also addressed. Such a study is hence performed in light of recent conflicting views on the causes of wake meandering: is the observed dynamic wake behaviour a result of large scale turbulent forcing or do more subtle and intrinsic wake instabilities play a role? This study concludes that the presence of the ground and external perturbations, most notably changes in the wake pitch and the rotor thrust coefficient, can significantly affect the steady development of the wake. The mutual vortex pairing instability, whilst displaying interesting periodic behaviour, does not correlate with periodic wake behaviour reported by Medici et al. However, in the absence of unsteady inflow, it is shown that the wake of a Horizontal Axis Wind Turbine (HAWT) is certainly prone to displaying unstable, dynamic behaviour caused by these additional factors

  7. Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear

    Science.gov (United States)

    Mendoza, Victor; Goude, Anders

    2017-05-01

    The current trend of the wind energy industry aims for large scale turbines installed in wind farms. This brings a renewed interest in vertical axis wind turbines (VAWTs) since they have several advantages over the traditional Horizontal Axis Wind Tubines (HAWTs) for mitigating the new challenges. However, operating VAWTs are characterized by complex aerodynamics phenomena, presenting considerable challenges for modeling tools. An accurate and reliable simulation tool for predicting the interaction between the obtained wake of an operating VAWT and the flow in atmospheric open sites is fundamental for optimizing the design and location of wind energy facility projects. The present work studies the wake produced by a VAWT and how it is affected by the surface roughness of the terrain, without considering the effects of the ambient turbulence intensity. This study was carried out using an actuator line model (ALM), and it was implemented using the open-source CFD library OpenFOAM to solve the governing equations and to compute the resulting flow fields. An operational H-shaped VAWT model was tested, for which experimental activity has been performed at an open site north of Uppsala-Sweden. Different terrains with similar inflow velocities have been evaluated. Simulated velocity and vorticity of representative sections have been analyzed. Numerical results were validated using normal forces measurements, showing reasonable agreement.

  8. Wind Turbine Wake Characterization from Temporally Disjunct 3-D Measurements

    Directory of Open Access Journals (Sweden)

    Paula Doubrawa

    2016-11-01

    Full Text Available Scanning LiDARs can be used to obtain three-dimensional wind measurements in and beyond the atmospheric surface layer. In this work, metrics characterizing wind turbine wakes are derived from LiDAR observations and from large-eddy simulation (LES data, which are used to recreate the LiDAR scanning geometry. The metrics are calculated for two-dimensional planes in the vertical and cross-stream directions at discrete distances downstream of a turbine under single-wake conditions. The simulation data are used to estimate the uncertainty when mean wake characteristics are quantified from scanning LiDAR measurements, which are temporally disjunct due to the time that the instrument takes to probe a large volume of air. Based on LES output, we determine that wind speeds sampled with the synthetic LiDAR are within 10% of the actual mean values and that the disjunct nature of the scan does not compromise the spatial variation of wind speeds within the planes. We propose scanning geometry density and coverage indices, which quantify the spatial distribution of the sampled points in the area of interest and are valuable to design LiDAR measurement campaigns for wake characterization. We find that scanning geometry coverage is important for estimates of the wake center, orientation and length scales, while density is more important when seeking to characterize the velocity deficit distribution.

  9. Wind Farm Wake: The Horns Rev Photo Case

    Directory of Open Access Journals (Sweden)

    Pierre-Elouan Réthoré

    2013-02-01

    Full Text Available The aim of the paper is to examine the nowadays well-known wind farm wake photographs taken on 12 February 2008 at the offshore Horns Rev 1 wind farm. The meteorological conditions are described from observations from several satellite sensors quantifying clouds, surface wind vectors and sea surface temperature as well as ground-based information at and near the wind farm, including Supervisory Control and Data Acquisition (SCADA data. The SCADA data reveal that the case of fog formation occurred 12 February 2008 on the 10:10 UTC. The fog formation is due to very special atmospheric conditions where a layer of cold humid air above a warmer sea surface re-condensates to fog in the wake of the turbines. The process is fed by warm humid air up-drafted from below in the counter-rotating swirl generated by the clock-wise rotating rotors. The condensation appears to take place primarily in the wake regions with relatively high axial velocities and high turbulent kinetic energy. The wind speed is near cut-in and most turbines produce very little power. The rotational pattern of spiraling bands produces the large-scale structure of the wake fog.

  10. An experimental and numerical study of the atmospheric stability impact on wind turbine wakes

    DEFF Research Database (Denmark)

    Machefaux, Ewan; Larsen, Gunner Chr.; Koblitz, Tilman

    2016-01-01

    In this paper, the impact of atmospheric stability on a wind turbine wake is studied experimentally and numerically. The experimental approach is based on full-scale (nacelle based) pulsed lidar measurements of the wake flow field of a stall-regulated 500 kW turbine at the DTU Wind Energy, Risø...... campus test site. Wake measurements are averaged within a mean wind speed bin of 1 m s1 and classified according to atmospheric stability using three different metrics: the Obukhov length, the Bulk–Richardson number and the Froude number. Three test cases are subsequently defined covering various...... atmospheric conditions. Simulations are carried out using large eddy simulation and actuator disk rotor modeling. The turbulence properties of the incoming wind are adapted to the thermal stratification using a newly developed spectral tensor model that includes buoyancy effects. Discrepancies are discussed...

  11. Using High-Fidelity Computational Fluid Dynamics to Help Design a Wind Turbine Wake

    OpenAIRE

    Churchfield, Matthew J.; Wang, Qi; Scholbrock, A.; Herges, T.; Mikkelsen, Torben Krogh; Sjöholm, Mikael

    2016-01-01

    We describe the process of using large-eddy simulations of wind turbine wake flow to help design a wake measurement campaign. The main goal of the experiment is to measure wakes and wake deflection that result from intentional yaw misalignment under a variety of atmospheric conditions at the Scaled Wind Farm Technology facility operated by Sandia National Laboratories in Lubbock, Texas. Prior simulation studies have shown that wake deflection may be used for wind-plant control that maximizes ...

  12. Towards a Wind Turbine Wake Reduced-Order Model

    Science.gov (United States)

    Hamilton, Nicholas; Viggiano, Bianca; Calaf, Marc; Tutkun, Murat; Cal, Raúl Bayoán

    2017-11-01

    A reduced-order model for a wind turbine wake is sought for prediction and control. Basis functions from the proper orthogonal decomposition (POD) represent the spatially coherent turbulence structures in the wake; eigenvalues delineate the turbulence kinetic energy associated with each mode. Back-projecting the POD modes onto the velocity snapshots produces coefficients that express the amplitude of each mode in time. A reduced-order model of the wind turbine wake (wakeROM) is defined through a series of polynomial parameters that quantify mode interaction and the evolution of each mode coefficient. Tikhonov regularization is employed to recalibrate the dynamical system, reducing error in the modeled mode coefficients and adding stability to the system. The wakeROM is periodically reinitialized by relating the incoming turbulent velocity to the POD mode coefficients. A high-level view of the wakeROM provides as a platform to discuss promising research direction, alternate processes that will enhance stability, and portability to control methods. NSF- ECCS-1032647, NSF-CBET-1034581, Research Council of Norway Project Number 231491.

  13. Flow and wakes in large wind farms. Final report for UpWind WP8

    Energy Technology Data Exchange (ETDEWEB)

    Barthelmie, R.J.; Frandsen, S.T.; Rathmann, O. (Risoe DTU (Denmark)); Hansen, K. (Technical Univ. of Denmark (DTU), Kgs. Lyngby (Denmark)); Politis, E.; Prospathopoulos, J. (CRES (Greece)); Schepers, J.G. (ECN, Petten (Netherlands)); Rados, K. (NTUA, Athens (Greece)); Cabezon, D. (CENER, Sarriguren (Spain)); Schlez, W.; Neubert, A.; Heath, M. (Garrad Hassan and Partners (Germany) (United Kingdom))

    2011-02-15

    This report summarises the research undertaken through the European Commission funded project UpWind Wp8:Flow. The objective of the work was to develop understanding of flow in large wind farms and to evaluate models of power losses due to wind turbine wakes focusing on complex terrain and offshore. A crosscutting activity was to improve and compare the performance of computational fluid dynamics models with wind farm models. The report contains 6 deliverable reports and guideline to wind farm wake analysis as appendices. (Author)

  14. Quantifying the Impact of Wind Turbine Wakes on Power Output at Offshore Wind Farms

    DEFF Research Database (Denmark)

    Barthelmie, Rebecca Jane; Pryor, Sara; Frandsen, Sten Tronæs

    2010-01-01

    There is an urgent need to develop and optimize tools for designing large wind farm arrays for deployment offshore. This research is focused on improving the understanding of, and modeling of, wind turbine wakes in order to make more accurate power output predictions for large offshore wind farms...

  15. Flow and wakes in large wind farms: Final report for UpWind WP8

    DEFF Research Database (Denmark)

    Barthelmie, Rebecca Jane; Frandsen, Sten Tronæs; Rathmann, Ole

    This report summarises the research undertaken through the European Commission funded project UpWind Wp8:Flow. The objective of the work was to develop understanding of flow in large wind farms and to evaluate models of power losses due to wind turbine wakes focusing on complex terrain and offsho...

  16. Wind turbine and actuator disc wake : Two experimental campaigns

    NARCIS (Netherlands)

    Lignarolo, L.; Ragni, D.; Simao Ferreira, C.J.; van Bussel, G.J.W.

    2015-01-01

    The present paper is the summary of 3 years of research on the wake aerodynamics of horizontal axis wind turbine at Delft University of Technology, the Netherlands. In particular, the main results and the conclusions of two experimental campaigns are collected. The underlying research question is:

  17. Wind turbine wake interactions; results from blind tests

    Science.gov (United States)

    Krogstad, Per-Åge; Sætran, Lars

    2015-06-01

    Results from three "Blind test" Workshops on wind turbine wake modeling are presented. While the first "Blind test" (BT1, 2011) consisted of a single model turbine located in a large wind tunnel, the complexity was increased for each new test in order to see how various models performed. Thus the next "Blind test" (BT2, 2012) had two turbines mounted in-line. This is a crucial test for models intended to predict turbine performances in a wind farm. In the last "Blind test" (BT3, 2013) the two turbines were again mounted in-line, but offset sideways so that the rotor of the downstream turbine only intersected half the wake from the upstream turbine. This case produces high dynamic loads and strong asymmetry in the wake. For each "Blind test" the turbine geometry and wind tunnel environment was specified and the participants were asked to predict the turbine performances, as well as the wake development to five diameters downstream of the second turbine. For the first two tests axisymmetry could be assumed if the influence of the towers was neglected. This was not possible in BT3 and therefore only fully 3D methods could be applied. In all tests the prediction scatter was surprisingly high.

  18. High resolution wind turbine wake measurements with a scanning lidar

    DEFF Research Database (Denmark)

    Herges, T. G.; Maniaci, D. C.; Naughton, B. T.

    2017-01-01

    High-resolution lidar wake measurements are part of an ongoing field campaign being conducted at the Scaled Wind Farm Technology facility by Sandia National Laboratories and the National Renewable Energy Laboratory using a customized scanning lidar from the Technical University of Denmark. One...

  19. A CFD code comparison of wind turbine wakes

    DEFF Research Database (Denmark)

    Laan, van der, Paul Maarten; Storey, R. C.; Sørensen, Niels N.

    2014-01-01

    A comparison is made between the EllipSys3D and SnS CFD codes. Both codes are used to perform Large-Eddy Simulations (LES) of single wind turbine wakes, using the actuator disk method. The comparison shows that both LES models predict similar velocity deficits and stream-wise Reynolds-stresses fo...

  20. Atmospheric stability-dependent infinite wind-farm models and the wake-decay coefficient

    OpenAIRE

    Peña, Alfredo; Rathmann, Ole

    2014-01-01

    We extend the infinite wind-farm boundary-layer (IWFBL) model of Frandsen to take into account atmospheric static stability effects. This extended model is compared with the IWFBL model of Emeis and to the Park wake model used inWind Atlas Analysis and Application Program (WAsP), which is computed for an infinite wind farm. The models show similar behavior for the wind-speed reduction when accounting for a number of surface roughness lengths, turbine to turbine separations and wind speeds und...

  1. Simulating coastal effects on an offshore wind farm

    DEFF Research Database (Denmark)

    van der Laan, Paul; Pena Diaz, Alfredo; Volker, Patrick

    Wind turbine wakes can cause energy losses in wind farms1 and their effect needs to be modeled in order to design energy efficient wind farm layouts. Wake losses in offshore wind farms are often modeled by assuming offshore conditions for all wind directions; however, many offshore wind farms...

  2. A New Analytical Model for Wind-Turbine Wakes

    Science.gov (United States)

    Bastankhah, Majid; Porté-Agel, Fernando

    2013-04-01

    The intention of this study is to propose and validate a simple and efficient analytical model for the prediction of the wake velocity downwind of a stand-alone wind-turbine. Extensive efforts have been carried out to model the wake region analytically. One of the most popular models, proposed by Jensen, assumes a top-hat distribution of the velocity deficit at any plane perpendicular to the wake. That model has been extensively used in the literature and commercial softwares, but it has two important limitations that should be pointed out: (a) Even though this model is supposed to satisfy momentum conservation, in reality mass conservation is only used to derive it; (b) the assumption of a top-hat distribution of the velocity deficit is expected to underestimate that deficit in the center of the wake, and overestimate it near the edge of the wake. In order to overcome the above-mentioned limitations, here we propose an alternative analytical model that satisfies both mass and momentum conservation, and assumes a Gaussian distribution of the velocity deficit. For this purpose, we apply momentum and mass conservation to two different control volumes which have been previously used in the context of analytical modeling of wakes. The velocity profiles obtained with our proposed model are in good agreement with large-eddy simulation data and experimental measurements. By contrast, the top hat models, as expected, clearly underestimate the velocity deficit at the center of the wake region and overestimate it near the edge of the wake.

  3. Vertical axis wind turbine wake in boundary layer flow in a wind tunnel

    Science.gov (United States)

    Rolin, Vincent; Porté-Agel, Fernando

    2016-04-01

    A vertical axis wind turbine is placed in a boundary layer flow in a wind tunnel, and its wake is investigated. Measurements are performed using an x-wire to measure two components of velocity and turbulence statistics in the wake of the wind turbine. The study is performed at various heights and crosswind positions in order to investigate the full volume of the wake for a range of tip speed ratios. The velocity deficit and levels of turbulence in the wake are related to the performance of the turbine. The asymmetric incoming boundary layer flow causes the rate of recovery in the wake to change as a function of height. Higher shear between the wake and unperturbed flow occurs at the top edge of the wake, inducing stronger turbulence and mixing in this region. The difference in flow relative to the blades causes the velocity deficit and turbulence level to change as a function of crosswind position behind the rotor. The relative difference diminishes with increasing tip speed ratio. Therefore, the wake becomes more homogeneous as tip speed ratio increases.

  4. Wind turbine wakes; power deficit in clusters and wind farms

    DEFF Research Database (Denmark)

    Hansen, Kurt Schaldemose; Barthelmie, Rebecca

    2012-01-01

    The purpose of this presentation is to present recent power deficit analysis based on wind farm measurements. The power deficit is used to validate wind farm prediction models for different inflow conditions......The purpose of this presentation is to present recent power deficit analysis based on wind farm measurements. The power deficit is used to validate wind farm prediction models for different inflow conditions...

  5. Three-dimensional structure of wind turbine wakes as measured by scanning lidar

    Science.gov (United States)

    Bodini, Nicola; Zardi, Dino; Lundquist, Julie K.

    2017-08-01

    The lower wind speeds and increased turbulence that are characteristic of turbine wakes have considerable consequences on large wind farms: turbines located downwind generate less power and experience increased turbulent loads. The structures of wakes and their downwind impacts are sensitive to wind speed and atmospheric variability. Wake characterization can provide important insights for turbine layout optimization in view of decreasing the cost of wind energy. The CWEX-13 field campaign, which took place between June and September 2013 in a wind farm in Iowa, was designed to explore the interaction of multiple wakes in a range of atmospheric stability conditions. Based on lidar wind measurements, we extend, present, and apply a quantitative algorithm to assess wake parameters such as the velocity deficits, the size of the wake boundaries, and the location of the wake centerlines. We focus on wakes from a row of four turbines at the leading edge of the wind farm to explore variations between wakes from the edge of the row (outer wakes) and those from turbines in the center of the row (inner wakes). Using multiple horizontal scans at different elevations, a three-dimensional structure of wakes from the row of turbines can be created. Wakes erode very quickly during unstable conditions and can in fact be detected primarily in stable conditions in the conditions measured here. During stable conditions, important differences emerge between the wakes of inner turbines and the wakes of outer turbines. Further, the strong wind veer associated with stable conditions results in a stretching of the wake structures, and this stretching manifests differently for inner and outer wakes. These insights can be incorporated into low-order wake models for wind farm layout optimization or for wind power forecasting.

  6. High-Order Numerical Simulations of Wind Turbine Wakes

    DEFF Research Database (Denmark)

    Kleusberg, E.; Mikkelsen, Robert Flemming; Schlatter, Philipp

    2017-01-01

    Previous attempts to describe the structure of wind turbine wakes and their mutual interaction were mostly limited to large-eddy and Reynolds-averaged Navier–Stokes simulations using finite-volume solvers. We employ the higher-order spectral-element code Nek5000 to study the influence of numerical...... the implementation with results from experimental campaigns undertaken at the Norwegian University of Science and Technology (NTNU Blind Tests), investigate parametric influences and compare computational aspects with existing numerical simulations. In general the results show good agreement between the experiments...... and the numerical simulations both for a single-turbine setup as well as a two-turbine setup where the turbines are offset in the spanwise direction. A shift in the wake center caused by the tower wake is detected similar to experiments. The additional velocity deficit caused by the tower agrees well...

  7. A Wind-Tunnel Simulation of the Wake of a Large Wind Turbine in a Weakly Unstable Boundary Layer

    Science.gov (United States)

    Hancock, P. E.; Zhang, S.

    2015-09-01

    Measurements have been made in the wake of a model wind turbine in both a weakly unstable and a baseline neutral atmospheric boundary layer, in the EnFlo stratified-flow wind tunnel, between 0.5 and 10 rotor diameters from the turbine, as part of an investigation of wakes in offshore winds. In the unstable case the velocity deficit decreases more rapidly than in the neutral case, largely because the boundary-layer turbulence levels are higher with consequent increased mixing. The height and width increase more rapidly in the unstable case, though still in a linear manner. The vertical heat flux decreases rapidly through the turbine, recovering to the undisturbed level first in the lower part of the wake, and later in the upper part, through the growth of an internal layer. At 10 rotor diameters from the turbine, the wake has strong features associated with the surrounding atmospheric boundary layer. A distinction is drawn between direct effects of stratification, as necessarily arising from buoyant production, and indirect effects, which arise only because the mean shear and turbulence levels are altered. Some aspects of the wake follow a similarity-like behaviour. Sufficiently far downstream, the decay of the velocity deficit follows a power law in the unstable case as well as the neutral case, but does so after a shorter distance from the turbine. Tentatively, this distance is also shorter for a higher loading on the turbine, while the power law itself is unaffected by turbine loading.

  8. Type-II entry of solar wind protons into the lunar wake: Effects of magnetic connection to the night-side surface

    Science.gov (United States)

    Nishino, Masaki N.; Fujimoto, Masaki; Saito, Yoshifumi; Tsunakawa, Hideo; Kasahara, Yoshiya; Kawamura, Mariko; Matsushima, Masaki; Takahashi, Futoshi; Shibuya, Hidetoshi; Shimizu, Hisayoshi; Goto, Yoshitaka; Hashimoto, Kozo; Omura, Yoshiharu; Kumamoto, Atsushi; Ono, Takayuki; Yokota, Shoichiro

    2014-05-01

    Our recent observations around the Moon revealed that so-called type-II (T2) entry of the solar wind protons into the near-Moon wake occurs when the IMF is dominated by the non-radial components (i.e. BY and/or BZ). Under this condition a part of the solar wind protons scattered/reflected at the lunar dayside surface subsequently enters the central region of the near-Moon wake after a large-scale cycloid motion, which accelerates electrons along the filed line into the wake. The situation handled in the previous studies is that the relevant magnetic field line is detached from the lunar surface, leaving a possibility of the T2 entry under magnetic connection left open. Here we report that the protons can access the central wake region that is magnetically connected to the lunar nightside surface, which we categorize into the T2 entry with magnetic connection to the lunar surface (T2MC). Furthermore we show that the energy of the electron beams induced by the proton entry into the wake depends on the magnetic connectivity. Strong electron acceleration (up to several hundred eV to 1 keV) along the magnetic field associated with the T2 entry is prominent when the field line has its both ends in the solar wind, that is, when the magnetic field is detached from the lunar surface (i.e. the previously-reported T2 entry that we rename to T2MD). On the other hand, no significant electron acceleration is found in the T2MC cases, although an enhancement of the electron flux associated with the T2 proton entry is evident. We also report that the T2 entry process takes place even under radial (BX-dominated) IMF condition. Our results indicate that, while the T2 entry of solar wind protons into the wake itself does not require a special IMF condition but is a rather general phenomenon, the characteristic energy of associated electrons does show a strong dependence on the magnetic connectivity to the lunar surface.

  9. Imaging doppler lidar for wind turbine wake profiling

    Science.gov (United States)

    Bossert, David J.

    2015-11-19

    An imaging Doppler lidar (IDL) enables the measurement of the velocity distribution of a large volume, in parallel, and at high spatial resolution in the wake of a wind turbine. Because the IDL is non-scanning, it can be orders of magnitude faster than conventional coherent lidar approaches. Scattering can be obtained from naturally occurring aerosol particles. Furthermore, the wind velocity can be measured directly from Doppler shifts of the laser light, so the measurement can be accomplished at large standoff and at wide fields-of-view.

  10. Wake Development of a Model Vertical Axis Wind Turbine

    Science.gov (United States)

    Kadum, Hawwa; Friedman, Sasha; Camp, Elizabeth; Cal, Rau'l.

    2015-11-01

    At the Portland State University wind tunnel facility, an experiment is conducted to observe the downstream development of the wake past a model vertical axis wind turbine (VAWT). The flow domain is composed of streamwise-spanwise planes at mid-height of the VAWT rotor and data is obtained via particle image velocimetry (PIV). The flow field is assessed by analyzing contours of mean velocities and the full Reynolds stress tensor. Furthermore, profiles of the aforementioned quantities and flow parameters are discussed in the context of downstream evolution/flow development.

  11. Role of subgrid-scale modeling in large eddy simulation of wind turbine wake interactions

    DEFF Research Database (Denmark)

    Sarlak, Hamid; Meneveau, C.; Sørensen, Jens Nørkær

    2015-01-01

    A series of simulations are carried out to evaluate specific features of the Large Eddy Simulation (LES) technique in wind turbine wake interactions. We aim to model wake interactions of two aligned model rotors. The effects of the rotor resolution, actuator line force filter size, and Reynolds...... number are investigated at certain tip speed ratios. The numerical results are validated against wind tunnel measurements in terms of the mean velocity, turbulence intensity and the power and thrust coefficients. Special emphasis is placed on the role played by subgrid scale (SGS) models in affecting...... the flow structures and turbine loading, as this has been studied less in prior investigations. It is found that, compared with the effects of rotor resolution and force kernel size, the SGS models have only a minor impact on the wake and predicted power performance. These observations confirm the usual...

  12. Wind and Wake Sensing with UAV Formation Flight: System Development and Flight Testing

    Science.gov (United States)

    Larrabee, Trenton Jameson

    Wind turbulence including atmospheric turbulence and wake turbulence have been widely investigated; however, only recently it become possible to use Unmanned Aerial Vehicles (UAVs) as a validation tool for research in this area. Wind can be a major contributing factor of adverse weather for aircraft. More importantly, it is an even greater risk towards UAVs because of their small size and weight. Being able to estimate wind fields and gusts can potentially provide substantial benefits for both unmanned and manned aviation. Possible applications include gust suppression for improving handling qualities, a better warning system for high wind encounters, and enhanced control for small UAVs during flight. On the other hand, the existence of wind can be advantageous since it can lead to fuel savings and longer duration flights through dynamic soaring or thermal soaring. Wakes are an effect of the lift distribution across an aircraft's wing or tail. Wakes can cause substantial disturbances when multiple aircraft are moving through the same airspace. In fact, the perils from an aircraft flying through the wake of another aircraft is a leading cause of the delay between takeoff times at airports. Similar to wind, though, wakes can be useful for energy harvesting and increasing an aircraft's endurance when flying in formation which can be a great advantage to UAVs because they are often limited in flight time due to small payload capacity. Formation flight can most often be seen in manned aircraft but can be adopted for use with unmanned systems. Autonomous flight is needed for flying in the "sweet spot" of the generated wakes for energy harvesting as well as for thermal soaring during long duration flights. For the research presented here formation flight was implemented for the study of wake sensing and gust alleviation. The major contributions of this research are in the areas of a novel technique to estimate wind using an Unscented Kalman filter and experimental wake

  13. The Explicit Wake Parametrisation V1.0: a wind farm parametrisation in the mesoscale model WRF

    Directory of Open Access Journals (Sweden)

    P. J. H. Volker

    2015-11-01

    Full Text Available We describe the theoretical basis, implementation, and validation of a new parametrisation that accounts for the effect of large offshore wind farms on the atmosphere and can be used in mesoscale and large-scale atmospheric models. This new parametrisation, referred to as the Explicit Wake Parametrisation (EWP, uses classical wake theory to describe the unresolved wake expansion. The EWP scheme is validated for a neutral atmospheric boundary layer against filtered in situ measurements from two meteorological masts situated a few kilometres away from the Danish offshore wind farm Horns Rev I. The simulated velocity deficit in the wake of the wind farm compares well to that observed in the measurements, and the velocity profile is qualitatively similar to that simulated with large eddy simulation models and from wind tunnel studies. At the same time, the validation process highlights the challenges in verifying such models with real observations.

  14. Influence of atmospheric stability on wind-turbine wakes: A large-eddy simulation study

    Science.gov (United States)

    Abkar, Mahdi; Porté-Agel, Fernando

    2014-05-01

    In this study, large-eddy simulation is combined with a turbine model to investigate the influence of atmospheric stability on wind-turbine wakes. In the simulations, subgrid-scale turbulent fluxes are parameterized using tuning-free Lagrangian scale-dependent dynamic models. These models optimize the local value of the model coefficients based on the dynamics of the resolved scales. The turbine-induced forces are parameterized with an actuator-disk model with rotation. In this technique, blade-element theory is used to calculate the lift and drag forces acting on the blades. Emphasis is placed on the structure and characteristics of wind-turbine wakes in the cases where the incident flows to the turbine have the same mean velocity at the hub height but different stability conditions. The simulation results show that atmospheric stability has a significant effect on the spatial distribution of the mean velocity deficit and turbulent fluxes in the wake region. In particular, the magnitude of the velocity deficit increases with increasing stability in the atmosphere. In addition, the locations of the maximum turbulence intensity and turbulent stresses are closer to the turbine in convective boundary layer compared with neutral and stable ones. Detailed analysis of the resolved turbulent kinetic energy (TKE) budget inside the wake reveals also that the thermal stratification of the incoming wind considerably affects the magnitude and spatial distribution of the turbulent production, transport term and dissipation rate (transfer of energy to the subgrid scales). It is also shown that the near-wake region can be extended to a farther distance downstream in stable condition compared with neutral and unstable counterparts. In order to isolate the effect of atmospheric stability, additional simulations of neutrally-stratified atmospheric boundary layers are performed with the same turbulence intensity at hub height as convective and stable ones. The results show that the

  15. 3D Volumetric Analysis of Wind Turbine Wake Properties in the Atmosphere Using High-Resolution Doppler Lidar

    Energy Technology Data Exchange (ETDEWEB)

    Banta, Robert M.; Pichugina, Yelena L.; Brewer, W. Alan; Lundquist, Julie K.; Kelley, Neil D.; Sandberg, Scott P.; Alvarez II, Raul J.; Hardesty, R. Michael; Weickmann, Ann M.

    2015-05-01

    Wind turbine wakes in the atmosphere are three-dimensional (3D) and time dependent. An important question is how best to measure atmospheric wake properties, both for characterizing these properties observationally and for verification of numerical, conceptual, and physical (e.g., wind tunnel) models of wakes. Here a scanning, pulsed, coherent Doppler lidar is used to sample a turbine wake using 3D volume scan patterns that envelop the wake and simultaneously measure the inflow profile. The volume data are analyzed for quantities of interest, such as peak velocity deficit, downwind variability of the deficit, and downwind extent of the wake, in a manner that preserves the measured data. For the case study presented here, in which the wake was well defined in the lidar data, peak deficits of up to 80% were measured 0.6-2 rotor diameters (D) downwind of the turbine, and the wakes extended more than 11D downwind. Temporal wake variability over periods of minutes and the effects of atmospheric gusts and lulls in the inflow are demonstrated in the analysis. Lidar scanning trade-offs important to ensuring that the wake quantities of interest are adequately sampled by the scan pattern, including scan coverage, number of scans per volume, data resolution, and scan-cycle repeat interval, are discussed.

  16. Comparative study on the wake deflection behind yawed wind turbine models

    Science.gov (United States)

    Schottler, Jannik; Mühle, Franz; Bartl, Jan; Peinke, Joachim; Adaramola, Muyiwa S.; Sætran, Lars; Hölling, Michael

    2017-05-01

    In this wind tunnel campaign, detailed wake measurements behind two different model wind turbines in yawed conditions were performed. The wake deflections were quantified by estimating the rotor-averaged available power within the wake. By using two different model wind turbines, the influence of the rotor design and turbine geometry on the wake deflection caused by a yaw misalignment of 30° could be judged. It was found that the wake deflections three rotor diameters downstream were equal while at six rotor diameters downstream insignificant differences were observed. The results compare well with previous experimental and numerical studies.

  17. Estimating the wake deflection downstream of a wind turbine in different atmospheric stabilities: an LES study

    Directory of Open Access Journals (Sweden)

    L. Vollmer

    2016-09-01

    Full Text Available An intentional yaw misalignment of wind turbines is currently discussed as one possibility to increase the overall energy yield of wind farms. The idea behind this control is to decrease wake losses of downstream turbines by altering the wake trajectory of the controlled upwind turbines. For an application of such an operational control, precise knowledge about the inflow wind conditions, the magnitude of wake deflection by a yawed turbine and the propagation of the wake is crucial. The dependency of the wake deflection on the ambient wind conditions as well as the uncertainty of its trajectory are not sufficiently covered in current wind farm control models. In this study we analyze multiple sources that contribute to the uncertainty of the estimation of the wake deflection downstream of yawed wind turbines in different ambient wind conditions. We find that the wake shapes and the magnitude of deflection differ in the three evaluated atmospheric boundary layers of neutral, stable and unstable thermal stability. Uncertainty in the wake deflection estimation increases for smaller temporal averaging intervals. We also consider the choice of the method to define the wake center as a source of uncertainty as it modifies the result. The variance of the wake deflection estimation increases with decreasing atmospheric stability. Control of the wake position in a highly convective environment is therefore not recommended.

  18. Impact of tower modeling on wind turbine wakes

    Science.gov (United States)

    Kleusberg, Elektra; Schlatter, Philipp; Henningson, Dan

    2017-11-01

    Recent research suggests the importance of modeling the support structure (tower and nacelle) when investigating the wake development behind wind turbines. These investigations are however mostly limited to low ambient turbulence levels which seldomly occur in field conditions. We present numerical simulations of wind turbine wakes using the actuator line method under different inflow conditions including varying turbulence levels and sheared inflow. The wind turbine, which employs the NREL S826 airfoil, is modeled after experiments conducted at the Norwegian University of Science and Technology. The rotor is investigated when perpendicular to the inflow and at a yaw angle of 30 degrees. The support structure is modeled using lift and drag body forces based on tabulated data. The simulations are performed with the spectral-element code Nek5000. After discussing the setup of the numerical domain and the turbulent inflow boundary condition, the influence of the tower model is characterized under turbulent, sheared and uniform inflow and the impact on downstream turbines is evaluated.

  19. Using High-Fidelity Computational Fluid Dynamics to Help Design a Wind Turbine Wake Measurement Experiment

    International Nuclear Information System (INIS)

    Churchfield, M; Wang, Q; Scholbrock, A; Herges, T; Mikkelsen, T; Sjöholm, M

    2016-01-01

    We describe the process of using large-eddy simulations of wind turbine wake flow to help design a wake measurement campaign. The main goal of the experiment is to measure wakes and wake deflection that result from intentional yaw misalignment under a variety of atmospheric conditions at the Scaled Wind Farm Technology facility operated by Sandia National Laboratories in Lubbock, Texas. Prior simulation studies have shown that wake deflection may be used for wind-plant control that maximizes plant power output. In this study, simulations are performed to characterize wake deflection and general behavior before the experiment is performed to ensure better upfront planning. Beyond characterizing the expected wake behavior, we also use the large-eddy simulation to test a virtual version of the lidar we plan to use to measure the wake and better understand our lidar scan strategy options. This work is an excellent example of a “simulation-in-the-loop” measurement campaign. (paper)

  20. Wind tunnel study of helical and straight-bladed vertical-axis wind turbine wakes

    Science.gov (United States)

    Bagheri, Maryam; Araya, Daniel

    2017-11-01

    It is hypothesized that blade curvature can serve as a passive means to control fluid entrainment and wake recovery in vertical-axis wind turbine (VAWT) arrays. We test this experimentally in a wind tunnel using two different VAWT configurations, one with straight blades and another with helical blades, keeping all other experimental parameters fixed. A small-scale, commercially available VAWT (15W max power) is used as the baseline wind tunnel model in each case. The commercial VAWT blades are replaced with either straight or helical blades that are 3D-printed extrusions of the same airfoil cross-section. Results from smoke flow visualization, three-component wake velocity measurements, and turbine power data are presented. These results give insight into the potential use of VAWTs with curved blades in utility-scale wind farms.

  1. Compressibility effects in planar wakes

    Science.gov (United States)

    Hickey, Jean-Pierre; Hussain, Fazle; Wu, Xiaohua

    2010-11-01

    Far-field, temporally evolving planar wakes are studied by DNS to evaluate the effect of compressibility on the flow. A high-order predictor-corrector code was developed and fully validated against canonical compressible test cases. In this study, wake simulations are performed at constant Reynolds number for three different Mach numbers: Ma= 0.2, 0.8 and 1.2. The domain is doubly periodic with a non-reflecting boundary in the cross-flow and is initialized by a randomly perturbed laminar profile. The compressibility of the flow modifies the observed structures which show greater three-dimensionality. A self-similar period develops in which the square of the wake half-width increase linearly with time and the Reynolds stress statistics at various times collapse using proper scaling parameters. The growth-rate increases with increasing compressibility of the flow: an observation which is substantiated by experimental results but is in stark contrast with the high-speed mixing-layer. As the growth-rate is related to the mixing ability of the flow, the impact of compressibility is of fundamental importance. Therefore, we seek an explanation of the modified growth-rate by investigating the turbulent kinetic energy equation. From the analysis, it can be conjectured that the pressure-strain term might play a role in the modified growth-rate.

  2. A wind-tunnel investigation of wind-turbine wakes in yawed conditions

    Science.gov (United States)

    Bastankhah, Majid; Porté-Agel, Fernando

    2015-06-01

    Wind-tunnel experiments were performed to study the performance of a model wind turbine and its wake characteristics in a boundary layer under different operating conditions, including different yaw angles and tip speed ratios. High-resolution particle image- velocimetry (PIV) was used to measure the three velocity components in a horizontal plane at hub height covering a broad streamwise range from upstream of the turbine to the far- wake region. Additionally, thrust and power coefficients of the turbine were measured under different conditions. These power and thrust measurements, together with the highly-resolved flow measurements, enabled us to systematically study different wake properties. The near-wake region is found to have a highly complex structure influenced by different factors such as tip speed ratio and wake rotation. In particular, for higher tip speed ratios, a noticeable speed-up region is observed in the central part of near wake, which greatly affects the flow distribution in this region. In this regard, the behavior of the near wake for turbines with similar thrust coefficients but different tip speed ratios can vary widely. In contrast, it is shown that the mean streamwise velocity in the far wake of the turbine with zero yaw angle has a self-similar Gaussian distribution, and the strength of wake in this region is consistent with the magnitude of the thrust coefficient. With increasing yaw angle, as expected, the power and thrust coefficients decrease, and the wake deflection increases. The measurements also reveal that, in addition to turbulent momentum flux, lateral mean momentum flux boosts the flow entrainment in only one side of the wake, which results in a faster wake recovery in that side. It is also found that the induced velocity upstream of a yawed turbine has a non-symmetric distribution, and its distribution is in agreement with the available model in the literature. Moreover, the results suggest that in order to accurately

  3. Dynamic wake model with coordinated pitch and torque control of wind farms for power tracking

    Science.gov (United States)

    Shapiro, Carl; Meyers, Johan; Meneveau, Charles; Gayme, Dennice

    2017-11-01

    Control of wind farm power production, where wind turbines within a wind farm coordinate to follow a time-varying power set point, is vital for increasing renewable energy participation in the power grid. Previous work developed a one-dimensional convection-diffusion equation describing the advection of the velocity deficit behind each turbine (wake) as well the turbulent mixing of the wake with the surrounding fluid. Proof-of-concept simulations demonstrated that a receding horizon controller built around this time-dependent model can effectively provide power tracking services by modulating the thrust coefficients of individual wind turbines. In this work, we extend this model-based controller to include pitch angle and generator torque control and the first-order dynamics of the drive train. Including these dynamics allows us to investigate control strategies for providing kinetic energy reserves to the grid, i.e. storing kinetic energy from the wind in the rotating mass of the wind turbine rotor for later use. CS, CM, and DG are supported by NSF (ECCS-1230788, CMMI 1635430, and OISE-1243482, the WINDINSPIRE project). JM is supported by ERC (ActiveWindFarms, 306471). This research was conducted using computational resources at MARCC.

  4. A coupled near and far wake model for wind turbine aerodynamics

    DEFF Research Database (Denmark)

    Pirrung, Georg R.; Aagaard Madsen, Helge; Kim, Taeseong

    2016-01-01

    a radial coupling between the blade sections and provides a computation of tip loss effects that depends on the actual blade geometry and the respective operating point. Moreover, the coupling of the NWM with a BEM theory-based far wake model is presented. To avoid accounting for the near wake induction......In this paper, an aerodynamic model consisting of a lifting line-based trailed vorticity model and a blade element momentum (BEM) model is described. The focus is on the trailed vorticity model, which is based on the near wake model (NWM) by Beddoes and has been extended to include the effects...... model and full rotor computational fluid dynamics (CFD) to evaluate the steady-state results in different cases. The model is shown to deliver good results across the whole operation range of the NREL 5-MW reference wind turbine....

  5. Study on offshore wind farm wakes based on Envisat ASAR, Radarsat-2 and Sentinel-1

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Badger, Merete; Badger, Jake

    Downstream of operating wind farms the mean wind speed is reduced as compared to the upwind conditions. In the offshore environment it is of particular interest to quantify the wind farm wake because turbine arrays are often located in the vicinity of other wind farms. The wakes reduce the annual....... The wind farm covers an area of around 4 km by 5 km and three concentric circles centered at the wind farm are used for extraction of results. The selected radii are 6, 10 and 13 km. The mean wind speeds in each of the three circles (geo-collocated) quantify the coastal wind speed gradient. Next step...

  6. Using High-Fidelity Computational Fluid Dynamics to Help Design a Wind Turbine Wake

    DEFF Research Database (Denmark)

    Churchfield, Matthew J.; Wang, Qi; Scholbrock, A.

    2016-01-01

    Wind Farm Technology facility operated by Sandia National Laboratories in Lubbock, Texas. Prior simulation studies have shown that wake deflection may be used for wind-plant control that maximizes plant power output. In this study, simulations are performed to characterize wake deflection and general...

  7. Velocity field and coherent structures in the near wake of a utility-scale wind turbine

    Science.gov (United States)

    Hong, Jiarong; Dasari, Teja; Wu, Yue; Liu, Yun

    2017-11-01

    Super-large-scale particle image velocity (SLPIV) and the associated flow visualization technique using natural snowfall have been shown as an effective tool to probe turbulent velocity field and coherent structures around utility-scale wind turbines (Hong et al. Nature Comm. 2014). Here we present a follow-up study using the data collected during multiple deployments from 2014 to 2016 around the 2.5 MW turbine at EOLOS field station. The data include SLPIV measurements in the near wake of the turbine in a field of view of 120 m (height) x 60 m (width), and the visualization of tip vortex behavior near the bottom blade tip over a broad range of turbine operational conditions. SLPIV results indicate a highly intermittent flow field in the near wake, consisting of both intense wake expansion and contraction events. Such intermittent states of the near wake are shown to be influenced by both the incoming wind conditions and the turbine operation. The visualization of tip vortex behavior demonstrates the presence of the state of consistent vortex formation as well as various types of disturbed vortex states. The occurrence of these states is statistically analyzed and is shown to be correlated with turbine operational and response parameters under different field conditions. National Science Foundation Fluid Dynamics Program.

  8. Atmospheric stability-dependent infinite wind-farm models and the wake-decay coefficient

    DEFF Research Database (Denmark)

    Peña, Alfredo; Rathmann, Ole

    2014-01-01

    We extend the infinite wind-farm boundary-layer (IWFBL) model of Frandsen to take into account atmospheric static stability effects. This extended model is compared with the IWFBL model of Emeis and to the Park wake model used inWind Atlas Analysis and Application Program (WAsP), which is computed......) larger than the adjusted values for a wide range of neutral to stable atmospheric stability conditions, a number of roughness lengths and turbine separations lower than _ 10 rotor diameters and (ii) too large compared with those obtained by a semiempirical formulation (relating the ratio of the friction...

  9. An All-Fiber, Modular, Compact Wind Lidar for Wind Sensing and Wake Vortex Applications

    Science.gov (United States)

    Prasad, Narasimha S.; Sibell, Russ; Vetorino, Steve; Higgins, Richard; Tracy, Allen

    2015-01-01

    This paper discusses an innovative, compact and eyesafe coherent lidar system developed for wind and wake vortex sensing applications. With an innovative all-fiber and modular transceiver architecture, the wind lidar system has reduced size, weight and power requirements, and provides enhanced performance along with operational elegance. This all-fiber architecture is developed around fiber seed laser coupled to uniquely configured fiber amplifier modules. The innovative features of this lidar system, besides its all fiber architecture, include pulsewidth agility and user programmable 3D hemispherical scanner unit. Operating at a wavelength of 1.5457 microns and with a PRF of up to 20 KHz, the lidar transmitter system is designed as a Class 1 system with dimensions of 30"(W) x 46"(L) x 60"(H). With an operational range exceeding 10 km, the wind lidar is configured to measure wind velocities of greater than 120 m/s with an accuracy of +/- 0.2 m/s and allow range resolution of less than 15 m. The dynamical configuration capability of transmitted pulsewidths from 50 ns to 400 ns allows high resolution wake vortex measurements. The scanner uses innovative liquid metal slip ring and is built using 3D printer technology with light weight nylon. As such, it provides continuous 360 degree azimuth and 180 degree elevation scan angles with an incremental motion of 0.001 degree. The lidar system is air cooled and requires 110 V for its operation. This compact and modular lidar system is anticipated to provide mobility, reliability, and ease of field deployment for wind and wake vortex measurements. Currently, this wind lidar is undergoing validation tests under various atmospheric conditions. Preliminary results of these field measurements of wind characteristics that were recently carried out in Colorado are discussed.

  10. Large-Eddy Simulation of Waked Turbines in a Scaled Wind Farm Facility

    Science.gov (United States)

    Wang, J.; McLean, D.; Campagnolo, F.; Yu, T.; Bottasso, C. L.

    2017-05-01

    The aim of this paper is to present the numerical simulation of waked scaled wind turbines operating in a boundary layer wind tunnel. The simulation uses a LES-lifting-line numerical model. An immersed boundary method in conjunction with an adequate wall model is used to represent the effects of both the wind turbine nacelle and tower, which are shown to have a considerable effect on the wake behavior. Multi-airfoil data calibrated at different Reynolds numbers are used to account for the lift and drag characteristics at the low and varying Reynolds conditions encountered in the experiments. The present study focuses on low turbulence inflow conditions and inflow non-uniformity due to wind tunnel characteristics, while higher turbulence conditions are considered in a separate study. The numerical model is validated by using experimental data obtained during test campaigns conducted with the scaled wind farm facility. The simulation and experimental results are compared in terms of power capture, rotor thrust, downstream velocity profiles and turbulence intensity.

  11. Developments of the offshore wind turbine wake model Fuga

    DEFF Research Database (Denmark)

    Ott, Søren; Nielsen, Morten

    with the modified equations. - Meandering. Meandering has been included in the form of a post processing of the model results that bend and twist the wake centreline. The meandering centrelines are calculated using a Gaussian process developed on the basis of measured spectra. An analysis of meteorological data...... from Horns Rev has been made in order to quantify the impact of non-stationarity of the wind direction. The results are generalized so as to account for the uncertainties imposed by a ten minute mean value trend as well as by the distance between turbines and the met mast. The old model has been...... with data is made. Even if the model predictions fall within estimated error bars, the model seems to over predict the measured efficiencies by a few percent. The model works best for unstable, neutral and light stable conditions whereas the results for stable and very stable conditions are questionable. We...

  12. Statistical meandering wake model and its application to yaw-angle optimisation of wind farms

    DEFF Research Database (Denmark)

    Thøgersen, Emil; Tranberg, Bo; Herp, Jürgen

    2017-01-01

    wakes are treated as independently and identically distributed random variables. When carefully calibrated to the Nysted wind farm, the ensemble average of the statistical model produces the same wind-direction dependence of the power efficiency as obtained from the standard Jensen model. Upon using...... the JWM to perform a yaw-angle optimisation of wind-farm power output, we find an optimisation gain of 6.7% for the Nysted wind farm when compared to zero yaw angles and averaged over all wind directions. When applying the obtained JWM-based optimised yaw angles to the SMWM, the ensemble-averaged gain......The wake produced by a wind turbine is dynamically meandering and of rather narrow nature. Only when looking at large time averages, the wake appears to be static and rather broad, and is then well described by simple engineering models like the Jensen wake model (JWM). We generalise the latter...

  13. Wind-tunnel study of the wake behind a vertical axis wind turbine in a boundary layer flow using stereoscopic particle image velocimetry

    Science.gov (United States)

    Rolin, V.; Porté-Agel, F.

    2015-06-01

    Stereo particle image velocimetry is used in a wind-tunnel to study boundary layer effects in the wake behind a vertical axis wind turbine. The turbine is a three-bladed giromill with a solidity of 1.18. The wake is studied for a tip speed ratio of 2 and an average chord Reynolds number of 1.6 × 104. The velocity deficit and turbulence levels in the horizontal plane are observed to be strongly asymmetrical with two strong peaks corresponding to the two halves of the rotor where blades move either towards the oncoming flow or away from it. The stronger peak is measured behind the blades moving upstream, however this region also benefits from a greater rate of re-energization. Due to the incoming boundary layer profile, momentum is also entrained downwards into the wake from above and aids with the recovery of the core of the wake.

  14. Effects of outer perturbances on dynamics of wake vortices

    International Nuclear Information System (INIS)

    Baranov, N.A.; Belotserkovsky, A.S.; Turchak, L.I.

    2004-01-01

    One of the problems in aircraft flight safety is reduction of the risk related with aircraft encounter with wake vortices generated by other aircraft. An efficient approach to this problem is design of systems providing information on areas of potential danger of wake vortices to pilots in real time. The main components of such a system are a unit for calculations of wake vortices behind aircraft and a unit for calculations of areas of potential danger. A promising way to development of real time algorithms for calculation of wake vortices is the use of vortex methods in CFD based on the hypothesis of quasi-3D flow in the area of wake vorticity. The mathematical model developed by our team calculates positions and intensity of wake vortices past aircraft taking account of such effects as viscous dissipation of vortices, effects of ambient turbulence, wind shear, as well as viscous interaction between wake vortices and the underlying surface. The necessity of including the last factor could be stems from the fact that in the case where wake vortices are in close proximity of the rigid surface, the viscous interaction between the wake vortices and the surface boundary layer results in the boundary layer separation changing the overall intensity and dynamics of the wake vortices. To evaluate the boundaries of the danger areas the authors use an approach based on calculation of additional aerodynamic forces and moments acting on the aircraft encountering wake vortices by means of evaluation of the aircraft additional velocities and angular rates corresponding to distribution of disturbed velocities on the aircraft surface. These criteria could be based on local characteristics of the vorticity areas or on characteristics related to the perturbation effects on the aircraft. The latter characteristics include the actual aerodynamic roll moment, the maximum angular rate or the maximum roll of the aircraft under perturbations in the wake vortices. To estimate the accuracy

  15. Comparison of the Dynamic Wake Meandering Model, Large-Eddy Simulation, and Field Data at the Egmond aan Zee Offshore Wind Plant: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Churchfield, M. J.; Moriarty, P. J.; Hao, Y.; Lackner, M. A.; Barthelmie, R.; Lundquist, J.; Oxley, G. S.

    2014-12-01

    The focus of this work is the comparison of the dynamic wake meandering model and large-eddy simulation with field data from the Egmond aan Zee offshore wind plant composed of 36 3-MW turbines. The field data includes meteorological mast measurements, SCADA information from all turbines, and strain-gauge data from two turbines. The dynamic wake meandering model and large-eddy simulation are means of computing unsteady wind plant aerodynamics, including the important unsteady meandering of wakes as they convect downstream and interact with other turbines and wakes. Both of these models are coupled to a turbine model such that power and mechanical loads of each turbine in the wind plant are computed. We are interested in how accurately different types of waking (e.g., direct versus partial waking), can be modeled, and how background turbulence level affects these loads. We show that both the dynamic wake meandering model and large-eddy simulation appear to underpredict power and overpredict fatigue loads because of wake effects, but it is unclear that they are really in error. This discrepancy may be caused by wind-direction uncertainty in the field data, which tends to make wake effects appear less pronounced.

  16. Observing and Simulating Wind-Turbine Wakes During the Evening Transition

    Science.gov (United States)

    Lee, Joseph C. Y.; Lundquist, Julie K.

    2017-09-01

    Wind-turbine-wake evolution during the evening transition introduces variability to wind-farm power production at a time of day typically characterized by high electricity demand. During the evening transition, the atmosphere evolves from an unstable to a stable regime, and vertical stratification of the wind profile develops as the residual planetary boundary layer decouples from the surface layer. The evolution of wind-turbine wakes during the evening transition is examined from two perspectives: wake observations from single turbines, and simulations of multiple turbine wakes using the mesoscale Weather Research and Forecasting (WRF) model. Throughout the evening transition, the wake's wind-speed deficit and turbulence enhancement are confined within the rotor layer when the atmospheric stability changes from unstable to stable. The height variations of maximum upwind-downwind differences of wind speed and turbulence intensity gradually decrease during the evening transition. After verifying the WRF-model-simulated upwind wind speed, wind direction and turbulent kinetic energy profiles with observations, the wind-farm-scale wake evolution during the evening transition is investigated using the WRF-model wind-farm parametrization scheme. As the evening progresses, due to the presence of the wind farm, the modelled hub-height wind-speed deficit monotonically increases, the relative turbulence enhancement at hub height grows by 50%, and the downwind surface sensible heat flux increases, reducing surface cooling. Overall, the intensifying wakes from upwind turbines respond to the evolving atmospheric boundary layer during the evening transition, and undermine the power production of downwind turbines in the evening.

  17. Wake Influence on Dynamic Load Characteristics of Offshore Floating Wind Turbines

    DEFF Research Database (Denmark)

    Jeon, Minu; Lee, Soogab; Kim, Taeseong

    2016-01-01

    Because the flow conditions of an offshore floating wind turbine and onshore fixed wind turbine differ, it is debatable whether the aerodynamic load predictions of an offshore floating wind turbine using the conventional blade-element momentum theory, which does not consider the dynamic wake effe...

  18. Active Power Control of Waked Wind Farms: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Fleming, Paul A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); van Wingerden, Jan-Willem [Delft University of Technology; Pao, Lucy [University of Colorado; Aho, Jacob [University of Colorado

    2017-08-15

    Active power control can be used to balance the total power generated by wind farms with the power consumed on the electricity grid. With the increasing penetration levels of wind energy, there is an increasing need for this ancillary service. In this paper, we show that the tracking of a certain power reference signal provided by the transmission system operator can be significantly improved by using feedback control at the wind farm level. We propose a simple feedback control law that significantly improves the tracking behavior of the total power output of the farm, resulting in higher performance scores. The effectiveness of the proposed feedback controller is demonstrated using high-fidelity computational fluid dynamics simulations of a small wind farm.

  19. Study of wind turbine wake modeling based on a modified actuator disk model and extended k-ε turbulence model

    DEFF Research Database (Denmark)

    Xu, Chang; Han, Xingxing; Wang, Xin

    2015-01-01

    This paper presented an improved computational fluid dynamics (CFD) model for simulating a horizontal-axis wind turbine wake. The model used the actuator disk model to simplify the wind turbine effect on the aerodynamic field by adding an extra momentum source and an improved term to correct...... the underestimation issue of the wind speed deficit when applying the STD k-ε model. In addition, the model also introduced a radial distribution function to assess the non-uniform load on the actuator disk and a coefficient C4ε of the turbulent source. To validate the model, the wind turbines of Nibe `B' and Dawin...

  20. IEA-Task 31 WAKEBENCH: Towards a protocol for wind farm flow model evaluation. Part 2: Wind farm wake models

    International Nuclear Information System (INIS)

    Moriarty, Patrick; Rodrigo, Javier Sanz; Gancarski, Pawel; Chuchfield, Matthew; Naughton, Jonathan W; Hansen, Kurt S; Machefaux, Ewan; Maguire, Eoghan; Castellani, Francesco; Terzi, Ludovico; Breton, Simon-Philippe; Ueda, Yuko

    2014-01-01

    Researchers within the International Energy Agency (IEA) Task 31: Wakebench have created a framework for the evaluation of wind farm flow models operating at the microscale level. The framework consists of a model evaluation protocol integrated with a web-based portal for model benchmarking (www.windbench.net). This paper provides an overview of the building-block validation approach applied to wind farm wake models, including best practices for the benchmarking and data processing procedures for validation datasets from wind farm SCADA and meteorological databases. A hierarchy of test cases has been proposed for wake model evaluation, from similarity theory of the axisymmetric wake and idealized infinite wind farm, to single-wake wind tunnel (UMN-EPFL) and field experiments (Sexbierum), to wind farm arrays in offshore (Horns Rev, Lillgrund) and complex terrain conditions (San Gregorio). A summary of results from the axisymmetric wake, Sexbierum, Horns Rev and Lillgrund benchmarks are used to discuss the state-of-the-art of wake model validation and highlight the most relevant issues for future development

  1. Wind tunnel study of the wind turbine interaction with a boundary-layer flow: Upwind region, turbine performance, and wake region

    Science.gov (United States)

    Bastankhah, M.; Porté-Agel, F.

    2017-06-01

    Comprehensive wind tunnel experiments were carried out to study the interaction of a turbulent boundary layer with a wind turbine operating under different tip-speed ratios and yaw angles. Force and power measurements were performed to characterize the variation of thrust force (both magnitude and direction) and generated power of the wind turbine under different operating conditions. Moreover, flow measurements, collected using high-resolution particle-image velocimetry as well as hot-wire anemometry, were employed to systematically study the flow in the upwind, near-wake, and far-wake regions. These measurements provide new insights into the effect of turbine operating conditions on flow characteristics in these regions. For the upwind region, the results show a strong lateral asymmetry under yawed conditions. For the near-wake region, the evolution of tip and root vortices was studied with the use of both instantaneous and phase-averaged vorticity fields. The results suggest that the vortex breakdown position cannot be determined based on phase-averaged statistics, particularly for tip vortices under turbulent inflow conditions. Moreover, the measurements in the near-wake region indicate a complex velocity distribution with a speed-up region in the wake center, especially for higher tip-speed ratios. In order to elucidate the meandering tendency of far wakes, particular focus was placed on studying the characteristics of large turbulent structures in the boundary layer and their interaction with wind turbines. Although these structures are elongated in the streamwise direction, their cross sections are found to have a size comparable to the rotor area, so that they can be affected by the presence of the turbine. In addition, the study of spatial coherence in turbine wakes reveals that any statistics based on streamwise velocity fluctuations cannot provide reliable information about the size of large turbulent structures in turbine wakes due to the effect of wake

  2. Aerodynamic optimization of wind turbine rotors using a blade element momentum method with corrections for wake rotation and expansion

    DEFF Research Database (Denmark)

    Døssing, Mads; Aagaard Madsen, Helge; Bak, Christian

    2012-01-01

    The blade element momentum (BEM) method is widely used for calculating the quasi-steady aerodynamics of horizontal axis wind turbines. Recently, the BEM method has been expanded to include corrections for wake expansion and the pressure due to wake rotation (), and more accurate solutions can now...... by the positive effect of wake rotation, which locally causes the efficiency to exceed the Betz limit. Wake expansion has a negative effect, which is most important at high tip speed ratios. It was further found that by using , it is possible to obtain a 5% reduction in flap bending moment when compared with BEM....... In short, allows fast aerodynamic calculations and optimizations with a much higher degree of accuracy than the traditional BEM model. Copyright © 2011 John Wiley & Sons, Ltd....

  3. Determination of real-time predictors of the wind turbine wake meandering

    Science.gov (United States)

    Muller, Yann-Aël; Aubrun, Sandrine; Masson, Christian

    2015-03-01

    The present work proposes an experimental methodology to characterize the unsteady properties of a wind turbine wake, called meandering, and particularly its ability to follow the large-scale motions induced by large turbulent eddies contained in the approach flow. The measurements were made in an atmospheric boundary layer wind tunnel. The wind turbine model is based on the actuator disc concept. One part of the work has been dedicated to the development of a methodology for horizontal wake tracking by mean of a transverse hot wire rake, whose dynamic response is adequate for spectral analysis. Spectral coherence analysis shows that the horizontal position of the wake correlates well with the upstream transverse velocity, especially for wavelength larger than three times the diameter of the disc but less so for smaller scales. Therefore, it is concluded that the wake is actually a rather passive tracer of the large surrounding turbulent structures. The influence of the rotor size and downstream distance on the wake meandering is studied. The fluctuations of the lateral force and the yawing torque affecting the wind turbine model are also measured and correlated with the wake meandering. Two approach flow configurations are then tested: an undisturbed incoming flow (modelled atmospheric boundary layer) and a disturbed incoming flow, with a wind turbine model located upstream. Results showed that the meandering process is amplified by the presence of the upstream wake. It is shown that the coherence between the lateral force fluctuations and the horizontal wake position is significant up to length scales larger than twice the wind turbine model diameter. This leads to the conclusion that the lateral force is a better candidate than the upstream transverse velocity to predict in real time the meandering process, for either undisturbed (wake free) or disturbed incoming atmospheric flows.

  4. Data Driven Modelling of the Dynamic Wake Between Two Wind Turbines

    DEFF Research Database (Denmark)

    Knudsen, Torben; Bak, Thomas

    2012-01-01

    turbine. This paper establishes flow models relating the wind speeds at turbines in a farm. So far, research in this area has been mainly based on first principles static models and the data driven modelling done has not included the loading of the upwind turbine and its impact on the wind speed downwind......Wind turbines in a wind farm, influence each other through the wind flow. Downwind turbines are in the wake of upwind turbines and the wind speed experienced at downwind turbines is hence a function of the wind speeds at upwind turbines but also the momentum extracted from the wind by the upwind....... This paper is the first where modern commercial mega watt turbines are used for data driven modelling including the upwind turbine loading by changing power reference. Obtaining the necessary data is difficult and data is therefore limited. A simple dynamic extension to the Jensen wake model is tested...

  5. Validation of a vortex ring wake model suited for aeroelastic simulations of floating wind turbines

    DEFF Research Database (Denmark)

    Vaal, J.B., de; Hansen, Martin Otto Laver; Moan, T.

    2014-01-01

    In order to evaluate aerodynamic loads on floating oshore wind turbines, advanced dynamic analysis tools are required. As a unied model that can represent both dynamic in ow and skewed in ow effects in it basic formulation, a wake model based on a vortex ring formulation is discussed. Such a model...... presents a good intermediate solution between computationally efficient but simple momentum balance methods and computationally expensive but complete computational fluid dynamics models. The model introduced is shown to be capable of modelling typical steady and unsteady test cases with reasonable...

  6. An improved k-ε model applied to a wind turbine wake in atmospheric turbulence

    DEFF Research Database (Denmark)

    Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan

    2015-01-01

    An improved k-ε turbulence model is developed and applied to a single wind turbine wake in a neutral atmospheric boundary layer using a Reynolds averaged Navier–Stokes solver. The proposed model includes a flow-dependent Cμ that is sensitive to high velocity gradients, e.g., at the edge of a wind...... turbine wake. The modified k-ε model is compared with the original k-ε eddy viscosity model, Large-Eddy Simulations and field measurements using eight test cases. The comparison shows that the velocity wake deficits, predicted by the proposed model are much closer to the ones calculated by the Large...

  7. Numerical Study of Wind Turbine Wake Modeling Based on a Actuator Surface Model

    DEFF Research Database (Denmark)

    Zhou, Huai-yang; Xu, Chang; Han, Xing Xing

    2017-01-01

    on the basis of actuator line model(ALM). By using ASM, the model of turbine can be simplified and the quantity of grids and computing time can be significantly reduced. A linear distribution model and a ASM Grid identification method are presented. This paper compares the ASM with ALM by computing both near...... and far wake of a Nibe A wind turbine, which combines wake velocity, turbulent intensity and vortex structure. Results show that ASM has better prediction accuracy and verify it's feasibility on numerical simulation of wind turbine wake....

  8. Investigating fundamental properties of wind turbine wake structure using particle image velocimetry

    Energy Technology Data Exchange (ETDEWEB)

    Whale, J. [Univ. of Edinburgh, Dept. of Mechanical Engineering, Edinburgh (United Kingdom)

    1997-08-01

    Low Reynolds number flow visualization tests are often used for showing the flow pattern changes associated with changes in lift-coefficients at a higher Reynolds number. In wind turbine studies, analysis of measured wake structures at small scale may reveal fundamental properties of the wake which will offer wake modellers a more complete understanding of rotor flows. Measurements are presented from experiments on a model wind turbine rig conducted in a water channel. The laser-optics technique of Particle Image Velocimetry (PIV) is used to make simultaneous multi-point measurements of the wake flow behind small-scale rotors. Analysis of the PIV data shows trends in velocity and vorticity structure in the wake. Study of the flow close to the rotor plane reveals information on stalled flow and blade performance. (au)

  9. IEA-Task 31 WAKEBENCH: Towards a protocol for wind farm flow model evaluation. Part 2: Wind farm wake models

    DEFF Research Database (Denmark)

    Moriarty, Patrick; Rodrigo, Javier Sanz; Gancarski, Pawel

    2014-01-01

    .windbench.net). This paper provides an overview of the building-block validation approach applied to wind farm wake models, including best practices for the benchmarking and data processing procedures for validation datasets from wind farm SCADA and meteorological databases. A hierarchy of test cases has been proposed...

  10. Wake losses from averaged and time-resolved power measurements at full scale wind turbines

    Science.gov (United States)

    Castellani, Francesco; Astolfi, Davide; Mana, Matteo; Becchetti, Matteo; Segalini, Antonio

    2017-05-01

    This work deals with the experimental analysis of wake losses fluctuations at full-scale wind turbines. The test case is a wind farm sited on a moderately complex terrain: 4 turbines are installed, having 2 MW of rated power each. The sources of information are the time-resolved data, as collected from the OPC server, and the 10-minutes averaged SCADA data. The objective is to compare the statistical distributions of wake losses for far and middle wakes, as can be observed through the “fast” lens of time-resolved data, for certain selected test-case time series, and through the “slow” lens of SCADA data, on a much longer time basis that allow to set the standards of the mean wake losses along the wind farm. Further, time-resolved data are used for an insight into the spectral properties of wake fluctuations, highlighting the role of the wind turbine as low-pass filter. Summarizing, the wind rose, the layout of the site and the structure of the data sets at disposal allow to study middle and far wake behavior, with a “slow” and “fast” perspective.

  11. Systematic Wind Farm Measurement Data Filtering Tool for Wake Model Calibration

    DEFF Research Database (Denmark)

    Rethore, Pierre-Elouan Mikael; Johansen, Nicholas Alan; Frandsen, Sten Tronæs

    A set of systematic methods for characterizing the sensors of a wind farm and using these sensors to filter more accurately large volumes of measurement data is proposed. These methods are based on the experience accumulated while processing datasets from two large offshore wind farms in Denmark....... Both wake model developers and wind farm operators seeking to determine how the wind farm operates under specific conditions can find these methods valuable. The methods are general and can be applied successfully to any wind farm by taking into consideration the specific aspects of each wind farm....

  12. Characterization of wind velocities in the wake of a full scale wind turbine using three ground-based synchronized WindScanners

    Science.gov (United States)

    Yazicioglu, Hasan; Angelou, Nikolas; Mikkelsen, Torben; José Trujillo, Juan

    2016-09-01

    The wind energy community is in need of detailed full-field measurements in the wake of wind turbines. Here, three dimensional(3D) wind vector field measurements obtained in the near-wake region behind a full-scale test turbine are presented. Specifically, the wake of a NEG Nordtank turbine, installed at Risoe test field, has been measured from 0 to 2 diameters downstream. For this, three ground-based synchronised short-range WindScanners and a spinner lidar have been used. The 3D wind velocity field has been reconstructed in horizontal and vertical planes crossing the hub. The 10-min mean values of the three wind components reveal detailed information regarding the wake properties while propagating downwind over flat terrain. Furthermore, the wake centre is tracked from the measurements and its meander is investigated as function of yaw misalignment of the turbine. The centre-line wake deficit is calculated both in a Nacelle and Moving Frame of Reference. The results can be used in quantitative validation of numerical wake models.

  13. Wake simulation for wind turbines with a free, prescribed- and hybrid-wake method

    Energy Technology Data Exchange (ETDEWEB)

    Bareiss, R.; Guidati, G.; Wagner, S. [Univ. Stuttgart, Inst. fuer Aerodynamik und Gasdynamik, Stuttgart (Germany)

    1997-08-01

    Calculations of the radial distribution and the time history of the induction factors have been performed with a number of different wake models implemented in a vortex-lattice method for tip-speed ratios in the range 1-13. The new models lead to a significant reduction of the computational effort down to 3-27% compared to a free-wake model with errors less than 5%. (au)

  14. Experimental Study on Influence of Pitch Motion on the Wake of a Floating Wind Turbine Model

    Directory of Open Access Journals (Sweden)

    Stanislav Rockel

    2014-03-01

    Full Text Available Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind turbine. Experimental results are compared with four wake models. The wake models employed are consistent with experimental results in describing the shapes and magnitudes of the streamwise velocity component of the wake for a fixed turbine. Inconsistencies between the model predictions and experimental results arise in the floating case particularly regarding the vertical displacement of the velocity components of the flow. Furthermore, it is found that the additional degrees of freedom of a floating wind turbine add to the complexity of the wake aerodynamics and improved wake models are needed, considering vertical flows and displacements due to pitch motion.

  15. Full-field assessment of wind turbine near-wake deviation in relation to yaw misalignment

    Directory of Open Access Journals (Sweden)

    J. J. Trujillo

    2016-04-01

    Full Text Available Presently there is a lack of data revealing the behaviour of the path followed by the near wake of full scale wind turbines and its dependence on yaw misalignment. Here we present an experimental analysis of the horizontal wake deviation of a 5 MW offshore wind turbine between 0.6 and 1.4 diameters downstream. The wake field has been scanned with a short-range lidar and the wake path has been reconstructed by means of two-dimensional Gaussian tracking. We analysed the measurements for rotor yaw misalignments arising in normal operation and during partial load, representing high thrust coefficient conditions. We classified distinctive wake paths with reference to yaw misalignment, based on the nacelle wind vane, in steps of 3° in a range of ±10.5°. All paths observed in the nacelle frame of reference showed a consistent convergence towards 0.9 rotor diameters downstream, suggesting a kind of wake deviation shift. This contrasts with published results from wind tunnels which in general report a convergence towards the rotor. The discrepancy is evidenced in particular in a comparison which we performed against published paths obtained by means of tip vortex tracking.

  16. Studying Wake Deflection of Wind Turbines in Yaw using Drag Disk Experiments and Actuator Disk Modeling in LES

    Science.gov (United States)

    Howland, Michael; Bossuyt, Juliaan; Meyers, Johan; Meneveau, Charles

    2015-11-01

    Recently, there has been a push towards the optimization in the power output of entire large wind farms through the control of individual turbines, as opposed to operating each turbine in a maximum power point tracking manner. In this vane, the wake deflection by wind turbines in yawed conditions has generated considerable interest in recent years. In order to effectively study the wake deflection according to classical actuator disk momentum theory, a 3D printed drag disk model with a coefficient of thrust of approximately 0.75 - 0.85 and a diameter of 3 cm is used, studied under uniform inflow in a wind tunnel with test section of 1 m by 1.3 m, operating with a negligible inlet turbulence level at an inflow velocity of 10 m/s. Mean velocity profile measurements are performed using Pitot probes. Different yaw angles are considered, including 10, 20, and 30 degrees. We confirm earlier results that (e.g.) a 30 degree yaw angle deflects the center of the wake around 1/2 of a rotor diameter when it impinges on a downstream turbine. Detailed comparisons between the experiments and Large Eddy Simulations using actuator disk model for the wind turbines are carried out in order to help validate the CFD model. Work supported by NSF (grants CBET-113380 and IIA-1243482, the WINDINSPIRE project) and by ERC (ActiveWindFarms, grant no. 306471).

  17. Comparison of two LES codes for wind turbine wake studies

    Science.gov (United States)

    Sarlak, H.; Pierella, F.; Mikkelsen, R.; Sørensen, J. N.

    2014-06-01

    For the third time a blind test comparison in Norway 2013, was conducted comparing numerical simulations for the rotor Cp and Ct and wake profiles with the experimental results. As the only large eddy simulation study among participants, results of the Technical University of Denmark (DTU) using their in-house CFD solver, EllipSys3D, proved to be more reliable among the other models for capturing the wake profiles and the turbulence intensities downstream the turbine. It was therefore remarked in the workshop to investigate other LES codes to compare their performance with EllipSys3D. The aim of this paper is to investigate on two CFD solvers, the DTU's in-house code, EllipSys3D and the open-sourse toolbox, OpenFoam, for a set of actuator line based LES computations. Two types of simulations are performed: the wake behind a signle rotor and the wake behind a cluster of three inline rotors. Results are compared in terms of velocity deficit, turbulence kinetic energy and eddy viscosity. It is seen that both codes predict similar near-wake flow structures with the exception of OpenFoam's simulations without the subgrid-scale model. The differences begin to increase with increasing the distance from the upstream rotor. From the single rotor simulations, EllipSys3D is found to predict a slower wake recovery in the case of uniform laminar flow. From the 3-rotor computations, it is seen that the difference between the codes is smaller as the disturbance created by the downstream rotors causes break down of the wake structures and more homogenuous flow structures. It is finally observed that OpenFoam computations are more sensitive to the SGS models.

  18. A simple and complete model for wind turbine wakes over complex terrain

    Science.gov (United States)

    Rommelfanger, Nick; Rajborirug, Mai; Luzzatto-Fegiz, Paolo

    2017-11-01

    Simple models for turbine wakes have been used extensively in the wind energy community, both as independent tools, as well as to complement more refined and computationally-intensive techniques. These models typically prescribe empirical relations for how the wake radius grows with downstream distance x and obtain the wake velocity at each x through the application of either mass conservation, or of both mass and momentum conservation (e.g. Katić et al. 1986; Frandsen et al. 2006; Bastankhah & Porté-Agel 2014). Since these models assume a global behavior of the wake (for example, linear spreading with x) they cannot respond to local changes in background flow, as may occur over complex terrain. Instead of assuming a global wake shape, we develop a model by relying on a local assumption for the growth of the turbulent interface. To this end, we introduce to wind turbine wakes the use of the entrainment hypothesis, which has been used extensively in other areas of geophysical fluid dynamics. We obtain two coupled ordinary differential equations for mass and momentum conservation, which can be readily solved with a prescribed background pressure gradient. Our model is in good agreement with published data for the development of wakes over complex terrain.

  19. A Stereo PIV Study on the Wake Characteristics behind Dual-Rotor Wind Turbines

    Science.gov (United States)

    Hu, Hui; Wang, Zhenyu; Tian, Wei

    2015-11-01

    We report an experimental study to investigate the aeromechanics and wake characteristics of dual-rotor wind turbines (DRWTs) with co- and counter-rotating configurations, 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 under neutral stability conditions. In addition to measuring the power outputs and dynamic wind loads acting on the SRWT and DRWT systems, a stereoscopic PIV was used for detailed wake flow field measurements (free-run and phase-locked) to quantify the characteristics of the turbulent turbine wake flow and to reveal visualize the evolution of the unsteady vortex structures in the wakes of DRWTs, in comparison with those behind a conventional SRWT systems. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate underlying physics for higher total power yield and better durability of the wind turbines. The funding support from the Iowa Energy Center with Grant No. 14-008-OG and National Science Foundation (NSF) with Grant Numbers of CBET-1133751 and CBET-1438099 is gratefully acknowledged.

  20. Wind Turbine Wake Characterization with Remote Sensing and Computational Fluid Dynamics

    Science.gov (United States)

    Aitken, Matthew Lawrence

    Because of the dense arrays at most wind farms, the region of disturbed flow downstream of an individual turbine leads to reduced power production and increased structural loading for its leeward counterparts. Currently, wind farm wake modeling, and hence turbine layout optimization, suffer from an unacceptable degree of uncertainty, largely because of a lack of adequate experimental data for model verification. Accordingly, wake measurements were taken in two separate experiments, (1) using the ground-based High Resolution Doppler Lidar (HRDL) developed by the National Oceanic and Atmospheric Administration (NOAA) in the Turbine Wake and Inflow Characterization Study (TWICS) at the National Renewable Energy Laboratory (NREL), and (2) using nacelle-based long-range lidar at a wind farm in the western United States. The vantage point from the nacelle is favorable in that scans can more consistently transect the central part of the wake. The work presented here outlines a set of quantitative procedures for determining critical parameters from these extensive datasets---such as the velocity deficit, the size of the wake boundary, and the location of the wake centerline---and the results are categorized by ambient wind speed, turbulence, and atmospheric stability. Despite specific reference to lidar, the methodology is general and can be applied to extract wake characteristics from other remote sensor datasets, as well as output from numerical simulations. In an effort to help advance computational fluid dynamics (CFD) models of wind turbine wake dynamics, experimental results are compared to a large eddy simulation (LES) of a turbine operating in the stable boundary layer using the actuator disk parameterization in the Weather Research and Forecasting (WRF) Model. With the wake characteristics described above as metrics for model verification, the simulations show good agreement with the observations. Moreover, new features---namely rotor tilt and drag from the

  1. Comparison of two LES codes for wind turbine wake studies

    DEFF Research Database (Denmark)

    Chivaee, Hamid Sarlak; Pierella, F.; Mikkelsen, Robert Flemming

    2014-01-01

    For the third time a blind test comparison in Norway 2013, was conducted comparing numerical simulations for the rotor Cp and Ct and wake profiles with the experimental results. As the only large eddy simulation study among participants, results of the Technical University of Denmark (DTU) using...... their in-house CFD solver, EllipSys3D, proved to be more reliable among the other models for capturing the wake profiles and the turbulence intensities downstream the turbine. It was therefore remarked in the workshop to investigate other LES codes to compare their performance with EllipSys3D. The aim...... of this paper is to investigate on two CFD solvers, the DTU's in-house code, EllipSys3D and the open-sourse toolbox, OpenFoam, for a set of actuator line based LES computations. Two types of simulations are performed: the wake behind a signle rotor and the wake behind a cluster of three inline rotors. Results...

  2. Experimental investigation of the wake behind a model of wind turbine in a water flume

    DEFF Research Database (Denmark)

    Okulov, Valery; Naumov, Igor; Kabardin, I.

    2014-01-01

    The flow behind the model of wind turbine rotor is investigated experimentally in a water flume using Particle Image Velocimetry. The study carried out involves rotors of three bladed wind turbine designed using Glauert’s optimization. The transitional regime, generally characterized as in between...... the regime governed by stable organized vortical structures and the turbulent wake, develops from disturbances of the tip and root vorticies through vortex paring and further complex behaviour towards the fully turbulent wake. Our PIV measurements pay special attention to the onset of the instabilities...

  3. Determination of Wind Turbine Near-Wake Length Based on Stability Analysis

    International Nuclear Information System (INIS)

    Sørensen, Jens N; Mikkelsen, Robert; Sarmast, Sasan; Ivanell, Stefan; Henningson, Dan

    2014-01-01

    A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equations using the actuator line (ACL) method. The wake is perturbed by applying stochastic or harmonic excitations in the neighborhood of the tips of the blades. The flow field is then analyzed to obtain the stability properties of the tip vortices in the wake of the wind turbine. As a main outcome of the study it is found that the amplification of specific waves (traveling structures) along the tip vortex spirals is responsible for triggering the instability leading to wake breakdown. The presence of unstable modes in the wake is related to the mutual inductance (vortex pairing) instability where there is an out-of-phase displacement of successive helix turns. Furthermore, using the non-dimensional growth rate, it is found that the pairing instability has a universal growth rate equal to π/2. Using this relationship, and the assumption that breakdown to turbulence occurs once a vortex has experienced sufficient growth, we provide an analytical relationship between the turbulence intensity and the stable wake length. The analysis leads to a simple expression for determining the length of the near wake. This expression shows that the near wake length is inversely proportional to thrust, tip speed ratio and the logarithmic of the turbulence intensity

  4. RANS simulations of wind turbine wakes: optimal tuning of turbulence closure and aerodynamic loads from LiDAR and SCADA data

    Science.gov (United States)

    Letizia, Stefano; Puccioni, Matteo; Zhan, Lu; Viola, Francesco; Camarri, Simone; Iungo, Giacomo Valerio

    2017-11-01

    Numerical simulations of wakes produced by utility-scale wind turbines still present challenges related to the variability of the atmospheric conditions and, in the most of the cases, the lack of information about the geometry and aerodynamic performance of the wind turbine blades. In order to overcome the mentioned difficulties, we propose a RANS solver for which turbine aerodynamic forcing and turbulence closure are calibrated through LiDAR and SCADA data acquired for an onshore wind farm. The wind farm under examination is located in North Texas over a relatively flat terrain. The experimental data are leveraged to maximize accuracy of the RANS predictions in terms of wake velocity field and power capture for different atmospheric stability conditions and settings of the wind turbines. The optimization of the RANS parameters is performed through an adjoint-RANS formulation and a gradient-based procedure. The optimally-tuned aerodynamic forcing and turbulence closure are then analyzed in order to investigate effects of the atmospheric stability on the evolution of wind turbine wakes and power performance. The proposed RANS solver has low computational costs comparable to those of wake engineering models, which make it a compelling tool for wind farm control and optimization. Acknowledgments: NSF I/UCRC WindSTAR IIP 1362033 and TACC.

  5. CFD Wake Modelling with a BEM Wind Turbine Sub-Model

    Directory of Open Access Journals (Sweden)

    Anders Hallanger

    2013-01-01

    Full Text Available Modelling of wind farms using computational fluid dynamics (CFD resolving the flow field around each wind turbine's blades on a moving computational grid is still too costly and time consuming in terms of computational capacity and effort. One strategy is to use sub-models for the wind turbines, and sub-grid models for turbulence production and dissipation to model the turbulent viscosity accurately enough to handle interaction of wakes in wind farms. A wind turbine sub-model, based on the Blade Momentum Theory, see Hansen (2008, has been implemented in an in-house CFD code, see Hallanger et al. (2002. The tangential and normal reaction forces from the wind turbine blades are distributed on the control volumes (CVs at the wind turbine rotor location as sources in the conservation equations of momentum. The classical k-epsilon turbulence model of Launder and Spalding (1972 is implemented with sub-grid turbulence (SGT model, see Sha and Launder (1979 and Sand and Salvesen (1994. Steady state CFD simulations were compared with flow and turbulence measurements in the wake of a model scale wind turbine, see Krogstad and Eriksen (2011. The simulated results compared best with experiments when stalling (boundary layer separation on the wind turbine blades did not occur. The SGT model did improve turbulence level in the wake but seems to smear the wake flow structure. It should be noted that the simulations are carried out steady state not including flow oscillations caused by vortex shedding from tower and blades as they were in the experiments. Further improvement of the simulated velocity defect and turbulence level seems to rely on better parameter estimation to the SGT model, improvements to the SGT model, and possibly transient- instead of steady state simulations.

  6. 3D wake measurements from a scanning wind lidar in combination with a fast wind field reconstruction model

    DEFF Research Database (Denmark)

    Mikkelsen, Torben Krogh; Herges, T. G.; Astrup, Poul

    2017-01-01

    High-resolution lidar wake measurements are part of an ongoing field campaign being conducted at the Scaled Wind Farm Technology (SWiFT) facility1 by Sandia National Laboratories and the National Renewable Energy Laboratory using a customized scanning “DTU SpinnerLidar”2 from the Technical...

  7. Wind Turbine Loads Induced by Terrain and Wakes: An Experimental Study through Vibration Analysis and Computational Fluid Dynamics

    Directory of Open Access Journals (Sweden)

    Francesco Castellani

    2017-11-01

    Full Text Available A wind turbine is a very well-known archetype of energy conversion system working at non-stationary regimes. Despite this, a deep mechanical comprehension of wind turbines operating in complicated conditions is still challenging, especially as regards the analysis of experimental data. In particular, wind turbines in complex terrain represent a very valuable testing ground because of the possible combination of wake effects among nearby turbines and flow accelerations caused by the terrain morphology. For these reasons, in this work, a cluster of four full-scale wind turbines from a very complex site is studied. The object of investigation is vibrations, at the level of the structure (tower and drive-train. Data collected by the on-board condition monitoring system are analyzed and interpreted in light of the knowledge of wind conditions and operating parameters collected by the Supervisory Control And Data Acquisition (SCADA. A free flow Computational Fluid Dynamics (CFD simulation is also performed, and it allows one to better interpret the vibration analysis. The main outcome is the interpretation of how wakes and flow turbulences appear in the vibration signals, both at the structural level and at the drive-train level. Therefore, this wind to gear approach builds a connection between flow phenomena and mechanical phenomena in the form of vibrations, representing a precious tool for assessing loads in different working conditions.

  8. Large Eddy Simulation of Vertical Axis Wind Turbine wakes; Part I: from the airfoil performance to the very far wake

    Science.gov (United States)

    Chatelain, Philippe; Duponcheel, Matthieu; Caprace, Denis-Gabriel; Marichal, Yves; Winckelmans, Gregoire

    2017-11-01

    A vortex particle-mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity-velocity formulation of the Navier-Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early development. Large-eddy simulation (LES) of vertical axis wind turbine (VAWT) flows is performed. The complex wake development is captured in detail and over up to 15 diameters downstream: from the blades to the near-wake coherent vortices and then through the transitional ones to the fully developed turbulent far wake (beyond 10 rotor diameters). The statistics and topology of the mean flow are studied with respect to the VAWT geometry and its operating point. The computational sizes also allow insights into the detailed unsteady vortex dynamics and topological flow features, such as a recirculation region influenced by the tip speed ratio and the rotor geometry.

  9. Numerical simulations of wake characteristics of a wind turbine in uniform inflow

    DEFF Research Database (Denmark)

    Troldborg, Niels; Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming

    2010-01-01

    The wake of a wind turbine operating in a uniform inflow at various tip speed ratios is simulated using a numerical method, which combines large eddy simulations with an actuator line technique. The computations are carried out in a numerical mesh with about 8.4·106 grid points distributed to fac...

  10. Estimation of wake propagation behind the rotors of wind-powered generators

    DEFF Research Database (Denmark)

    Naumov, I. V.; Mikkelsen, Robert Flemming; Okulov, Valery

    2016-01-01

    The objectives of this work are to develop the experimental model of wake behind the wind-power generator rotor to estimate its propagation distance and the impact on the average and pulsation characteristics of incident flow with the possibility of further use of these data in the calculation mo...

  11. A simple atmospheric boundary layer model applied to large eddy simulations of wind turbine wakes

    DEFF Research Database (Denmark)

    Troldborg, Niels; Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming

    2014-01-01

    A simple model for including the influence of the atmospheric boundary layer in connection with large eddy simulations of wind turbine wakes is presented and validated by comparing computed results with measurements as well as with direct numerical simulations. The model is based on an immersed...

  12. A wind turbine wake in changing atmospheric conditions: LES and lidar measurements

    Science.gov (United States)

    Vollmer, L.; C-Y Lee, J.; Steinfeld, G.; Lundquist, J. K.

    2017-05-01

    This work aims to reproduce the measured atmospheric conditions during one day of the CWEX-11 campaign, with a transient LES. The selected period includes several interesting atmospheric conditions for wind power generation such as a nocturnal low-level jet, a highly turbulent convective daytime boundary layer, as well as a distinct evening transition between daytime and nocturnal boundary layers. To include synoptic conditions, large-scale forcing profiles for the LES were derived from a mesoscale simulation with the WRF model. A comparison with lidar measurements shows that the trend of the wind conditions and the diurnal cycle is well replicated by the model chain. Selected periods of the day are simulated with the NREL 5MW turbine model, followed by a qualitative comparison of measured and simulated wakes. We find a strong dependency of the meandering and the shape of the wake on wind profile and turbulence, while a categorization by Obukhov length is less representative for the different conditions. As the veer in the wind profile increases, the deviation of the wind direction at hub height from the direction of the largest wake impact also increases.

  13. Numerical investigation of the wake interaction between two model wind turbines with span-wise offset

    DEFF Research Database (Denmark)

    Sarmast, Sasan; Chivaee, Hamid Sarlak; Ivanell, Stefan

    2014-01-01

    Wake interaction between two model scale wind turbines with span-wise offset is investigated numerically using Large Eddy Simulation (LES) and the results are validated against the experimental data. An actuator line technique is used for modeling the rotor. The investigated setup refers...... to a series of experimental measurements of two model scale turbines conducted by NTNU in low speed wind tunnel in which the two wind turbines are aligned with a span-wise offset resulting in half wake interaction. Two levels of free-stream turbulence are tested, the minimum undisturbed level of about Ti ≈ 0.......23% and a high level of about Ti ≈ 10% using a passive upstream grid. The results show that the rotor characteristics for both rotors are well captured numerically even if the downstream rotor operates into stall regimes. There are however some difficulties in correct prediction of the thrust level...

  14. Uncertainties and Wakes for Short-term Power Production of a Wind Farm

    DEFF Research Database (Denmark)

    Göçmen, Tuhfe; Giebel, Gregor

    2018-01-01

    Similar to the conventional power plants, the wind farms are expected to contribute to the grid stability and communicate with the system operators regarding the potential power production on much shorter time scales than AEP or even 10-min. Additionally, increasing interest to aerodynamic control...... of wind farms, both in the research community and in the industry, necessitates the wake models to be more accurate and reliable at shorter intervals. In this study, we discuss the uncertainties attached to an engineering wake model derived for 1-sec turbine data, and investigate the methods for reducing...... the uncertainty of such an application via further training the model for the wind farm and the time period in question using the historical data....

  15. Modeling large offshore wind farms under different atmospheric stability regimes with the Park wake model

    DEFF Research Database (Denmark)

    Pena Diaz, Alfredo; Réthoré, Pierre-Elouan; Rathmann, Ole

    2014-01-01

    We evaluate a modified version of the Park wake model against power data from a west-east row in the middle of the Horns Rev I offshore wind farm. The evaluation is performed on data classified in four different atmospheric stability conditions, for a narrow wind speed range, and a wide range...... turbines on the row and those using the WAsP recommended value closer to the data for the first turbines. It is generally seen that under stable and unstable atmospheric conditions the power deficits are the highest and lowest, respectively, but the wind conditions under both stability regimes...

  16. Modeling large offshore wind farms under different atmospheric stability regimes with the Park wake model

    DEFF Research Database (Denmark)

    Peña, Alfredo; Réthoré, Pierre-Elouan; Rathmann, Ole

    2013-01-01

    Here, we evaluate a modified version of the Park wake model against power data from a west-east row in the middle of the Horns Rev I offshore wind farm. The evaluation is performed on data classified in four different atmospheric stability conditions, for a narrow wind speed range, and a wide range...... turbines and those using the WAsP recommended value closer to the data for the first turbines. It is generally seen that under stable and unstable atmospheric conditions the power deficits are the highest and lowest, respectively, but the wind conditions under both stability regimes are different...

  17. Wind Farm Wake: The Horns Rev Photo Case

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Rasmussen, Leif; Peña, Alfredo

    2013-01-01

    surface temperature as well as ground-based information at and near the wind farm, including Supervisory Control and Data Acquisition (SCADA) data. The SCADA data reveal that the case of fog formation occurred 12 February 2008 on the 10:10 UTC. The fog formation is due to very special atmospheric...

  18. Classification of Rotor Induced Shearing Events in the Near Wake of a Wind Turbine Array Boundary Layer

    Science.gov (United States)

    Smith, Sarah; Viggiano, Bianca; Ali, Naseem; Cal, Raul Bayoan

    2017-11-01

    Flow perturbation induced by a turbine rotor imposes considerable turbulence and shearing effects in the near wake of a turbine, altering the efficiency of subsequent units within a wind farm array. Previous methods have characterized near wake vorticity of a turbine and recovery distance of various turbine array configurations. This study aims to build on previous analysis with respect to a turbine rotor within an array and develop a model to examine stress events and energy contribution in the near wake due to rotational effects. Hot wire anemometry was employed downstream of a turbine centrally located in the third row of a 3x3 array. Data considered points planar to the rotor and included simultaneous streamwise and wall-normal velocities as well as concurrent streamwise and transverse velocities. Conditional analysis of Reynolds stresses induced by the rotor agree with former near wake research, and examination of stresses in terms of streamwise and transverse velocity components depicts areas of significant rotational effects. Continued analysis includes spectral decomposition and conditional statistics to further characterize shearing events at various points considering the swept area of the rotor.

  19. Comparisons between the Wake of a Wind Turbine Generator Operated at Optimal Tip Speed Ratio and the Wake of a Stationary Disk

    Directory of Open Access Journals (Sweden)

    Takanori Uchida

    2011-01-01

    Full Text Available The wake of a wind turbine generator (WTG operated at the optimal tip speed ratio is compared to the wake of a WTG with its rotor replaced by a stationary disk. Numerical simulations are conducted with a large eddy simulation (LES model using a nonuniform staggered Cartesian grid. The results from the numerical simulations are compared to those from wind-tunnel experiments. The characteristics of the wake of the stationary disk are significantly different from those of the WTG. The velocity deficit at a downstream distance of 10 (: rotor diameter behind the WTG is approximately 30 to 40% of the inflow velocity. In contrast, flow separation is observed immediately behind the stationary disk (≤2, and the velocity deficit in the far wake (10 of the stationary disk is smaller than that of the WTG.

  20. PIV and LDA measurements of the wake behind a wind turbine model

    Science.gov (United States)

    Naumov, I. V.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.

    2014-06-01

    In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 - 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed.

  1. Towards reduced order modelling for predicting the dynamics of coherent vorticity structures within wind turbine wakes.

    Science.gov (United States)

    Debnath, M; Santoni, C; Leonardi, S; Iungo, G V

    2017-04-13

    The dynamics of the velocity field resulting from the interaction between the atmospheric boundary layer and a wind turbine array can affect significantly the performance of a wind power plant and the durability of wind turbines. In this work, dynamics in wind turbine wakes and instabilities of helicoidal tip vortices are detected and characterized through modal decomposition techniques. The dataset under examination consists of snapshots of the velocity field obtained from large-eddy simulations (LES) of an isolated wind turbine, for which aerodynamic forcing exerted by the turbine blades on the atmospheric boundary layer is mimicked through the actuator line model. Particular attention is paid to the interaction between the downstream evolution of the helicoidal tip vortices and the alternate vortex shedding from the turbine tower. The LES dataset is interrogated through different modal decomposition techniques, such as proper orthogonal decomposition and dynamic mode decomposition. The dominant wake dynamics are selected for the formulation of a reduced order model, which consists in a linear time-marching algorithm where temporal evolution of flow dynamics is obtained from the previous temporal realization multiplied by a time-invariant operator.This article is part of the themed issue 'Wind energy in complex terrains'. © 2017 The Author(s).

  2. Towards reduced order modelling for predicting the dynamics of coherent vorticity structures within wind turbine wakes

    Science.gov (United States)

    Debnath, M.; Santoni, C.; Leonardi, S.; Iungo, G. V.

    2017-03-01

    The dynamics of the velocity field resulting from the interaction between the atmospheric boundary layer and a wind turbine array can affect significantly the performance of a wind power plant and the durability of wind turbines. In this work, dynamics in wind turbine wakes and instabilities of helicoidal tip vortices are detected and characterized through modal decomposition techniques. The dataset under examination consists of snapshots of the velocity field obtained from large-eddy simulations (LES) of an isolated wind turbine, for which aerodynamic forcing exerted by the turbine blades on the atmospheric boundary layer is mimicked through the actuator line model. Particular attention is paid to the interaction between the downstream evolution of the helicoidal tip vortices and the alternate vortex shedding from the turbine tower. The LES dataset is interrogated through different modal decomposition techniques, such as proper orthogonal decomposition and dynamic mode decomposition. The dominant wake dynamics are selected for the formulation of a reduced order model, which consists in a linear time-marching algorithm where temporal evolution of flow dynamics is obtained from the previous temporal realization multiplied by a time-invariant operator. This article is part of the themed issue 'Wind energy in complex terrains'.

  3. Generalized coupled wake boundary layer model: applications and comparisons with field and LES data for two wind farms

    NARCIS (Netherlands)

    Stevens, Richard Johannes Antonius Maria; Gayme, Dennice F.; Meneveau, Charles

    2016-01-01

    We describe a generalization of the coupled wake boundary layer (CWBL) model for wind farms that can be used to evaluate the performance of wind farms under arbitrary wind inflow directions, whereas the original CWBL model (Stevens et al., J. Renewable and Sustainable Energy 7, 023115 (2015))

  4. Wind field re-construction of 3D Wake measurements from a turbine-installed scanning lidar

    DEFF Research Database (Denmark)

    Mikkelsen, Torben Krogh; Herges, Tommy; Astrup, Poul

    High-resolution wake flow measurements obtained from a turbine-mounted scanning lidar have been obtained from 1D to 5D behind a V27 test turbine. The measured line-of-sight projected wind speeds have, in connection with a fast CFD wind field reconstruction model, been used to generate 3D wind fie...

  5. Typhoon effect on Kuroshio and Green Island wake: a modelling study

    OpenAIRE

    T.-W. Hsu; M.-H. Chou; T.-H. Hou; S.-J. Liang

    2015-01-01

    Green Island located in the typhoon active eastern Taiwan coastal water is the potential Kuroshio power plant site. In this study, a high resolution (250–2250 m) shallow-water equations (SWEs) model is used to investigate the effect of typhoon on the hydrodynamics of Kuroshio and Green Island wake. Two wind induced flows, typhoon Soulik and Holland's wind field model, are studied. Simulation results of the typhoon Soulik indicate that salient characteristics of Kuroshio and ...

  6. On the Evolution of the Integral Length Scale in the Wake of Wind Turbines and within Wind Farms

    Science.gov (United States)

    Liu, Huiwen; Jin, Yaqing; Hayat, Imran; Chamorro, Leonardo P.

    2017-11-01

    Wind tunnel experiments were performed to characterize the evolution of integral length scale in the wake of a single turbine, and around wind farms. Hotwire anemometry was used to obtain high-resolution measurements of the streamwise velocity fluctuation at various locations. Negligible and high freestream turbulence levels were considered in the case of single turbine. The integral length scale along the rotor axis is found to grow nearly linearly with distance independent of the incoming turbulence levels, and appears to reach the incoming level in the high turbulence case at about 35-40 rotor diameters downstream. In the wind farm, results suggest that the distribution of integral length scale can be roughly described by a power-law growth with distance within consecutive turbines. Approximately past the third row, the integral length scale appears to reach equilibrium of the spatial distribution.

  7. Free wake analysis of wind turbine aerodynamics. Wind energy conversion. ASRL-TR-184-14

    Energy Technology Data Exchange (ETDEWEB)

    Gohard, J.C.

    1978-09-01

    The underlying theory is presented for determining blade and rotor/tower vibration and dynamic stability characteristics as well as the basic dynamic (as opposed to aerodynamic) operating loads. Starting with a simple concept of equivalent hinged rotors, the equations of motion for the blade including pitch, flap and lag motions are developed. The nonlinear equations are derived first and linearized about a finite displacement of the blade out of the plane of rotation. This is important since wind turbines tend to operate at relatively high coning angles. The effect of distributed flexibility, as opposed to the equivalent hinge concept, is then discussed.

  8. Improvements in ECN Wake Model

    Energy Technology Data Exchange (ETDEWEB)

    Versteeg, M.C. [University of Twente, Enschede (Netherlands); Ozdemir, H.; Brand, A.J. [ECN Wind Energy, Petten (Netherlands)

    2013-08-15

    Wind turbines extract energy from the flow field so that the flow in the wake of a wind turbine contains less energy and more turbulence than the undisturbed flow, leading to less energy extraction for the downstream turbines. In large wind farms, most turbines are located in the wake of one or more turbines causing the flow characteristics felt by these turbines differ considerably from the free stream flow conditions. The most important wake effect is generally considered to be the lower wind speed behind the turbine(s) since this decreases the energy production and as such the economical performance of a wind farm. The overall loss of a wind farm is very much dependent on the conditions and the lay-out of the farm but it can be in the order of 5-10%. Apart from the loss in energy production an additional wake effect is formed by the increase in turbulence intensity, which leads to higher fatigue loads. In this sense it becomes important to understand the details of wake behavior to improve and/or optimize a wind farm layout. Within this study improvements are presented for the existing ECN wake model which constructs the fundamental basis of ECN's FarmFlow wind farm wake simulation tool. The outline of this paper is as follows: first, the governing equations of the ECN wake farm model are presented. Then the near wake modeling is discussed and the results compared with the original near wake modeling and EWTW (ECN Wind Turbine Test Site Wieringermeer) data as well as the results obtained for various near wake implementation cases are shown. The details of the atmospheric stability model are given and the comparison with the solution obtained for the original surface layer model and with the available data obtained by EWTW measurements are presented. Finally the conclusions are summarized.

  9. Wake losses optimization of offshore wind farms with moveable floating wind turbines

    International Nuclear Information System (INIS)

    Rodrigues, S.F.; Teixeira Pinto, R.; Soleimanzadeh, M.; Bosman, Peter A.N.; Bauer, P.

    2015-01-01

    Highlights: • We present a layout optimization framework for wind farms with moveable turbines. • Using moveable wind turbines in optimized layouts maximizes energy production. • Turbine and wind farm designers should cooperate to optimize offshore wind projects. - Abstract: In the future, floating wind turbines could be used to harvest energy in deep offshore areas where higher wind mean speeds are observed. Currently, several floating turbine concepts are being designed and tested in small scale projects; in particular, one concept allows the turbine to move after installation. This article presents a novel layout optimization framework for wind farms composed of moveable floating turbines. The proposed framework uses an evolutionary optimization strategy in a nested configuration which simultaneously optimizes the anchoring locations and the wind turbine position within the mooring lines for each individual wind direction. The results show that maximum energy production is obtained when moveable wind turbines are deployed in an optimized layout. In conclusion, the framework represents a new design optimization tool for future offshore wind farms composed of moveable floating turbines

  10. Impact of the Diurnal Cycle of the Atmospheric Boundary Layer on Wind-Turbine Wakes: A Numerical Modelling Study

    Science.gov (United States)

    Englberger, Antonia; Dörnbrack, Andreas

    2018-03-01

    The wake characteristics of a wind turbine for different regimes occurring throughout the diurnal cycle are investigated systematically by means of large-eddy simulation. Idealized diurnal cycle simulations of the atmospheric boundary layer are performed with the geophysical flow solver EULAG over both homogeneous and heterogeneous terrain. Under homogeneous conditions, the diurnal cycle significantly affects the low-level wind shear and atmospheric turbulence. A strong vertical wind shear and veering with height occur in the nocturnal stable boundary layer and in the morning boundary layer, whereas atmospheric turbulence is much larger in the convective boundary layer and in the evening boundary layer. The increased shear under heterogeneous conditions changes these wind characteristics, counteracting the formation of the night-time Ekman spiral. The convective, stable, evening, and morning regimes of the atmospheric boundary layer over a homogeneous surface as well as the convective and stable regimes over a heterogeneous surface are used to study the flow in a wind-turbine wake. Synchronized turbulent inflow data from the idealized atmospheric boundary-layer simulations with periodic horizontal boundary conditions are applied to the wind-turbine simulations with open streamwise boundary conditions. The resulting wake is strongly influenced by the stability of the atmosphere. In both cases, the flow in the wake recovers more rapidly under convective conditions during the day than under stable conditions at night. The simulated wakes produced for the night-time situation completely differ between heterogeneous and homogeneous surface conditions. The wake characteristics of the transitional periods are influenced by the flow regime prior to the transition. Furthermore, there are different wake deflections over the height of the rotor, which reflect the incoming wind direction.

  11. Results of wake simulations at the Horns Rev I and Lillgrund wind farms using the modified Park model

    DEFF Research Database (Denmark)

    Peña, Alfredo; Réthoré, Pierre-Elouan; Hasager, Charlotte Bay

    This document reports on the results of the wake simulations performed at both the Horns Rev I and Lillgrund oshore wind farms using the modified Park model for the benchmark cases established under the project EERA-DTOC and the IEC Wind Task Wakebench. It also illustrates the comparison between...... are post-processed to partly take into account the wind direction uncertainty and when the wake decay coefficient is estimated either as function of the roughness, height, and atmospheric stability or turbulence intensity. For Lillgrund, the trends of the simulations and the observations are generally...

  12. The near wake structure and the development of vorticity behind a model horizontal axis wind turbine

    Energy Technology Data Exchange (ETDEWEB)

    Ebert, P.; Wood, D. [The Univ. of Newcastle, Dept. of Mechanical Engineering, Callaghan (Australia)

    1997-08-01

    The wake of a two bladed model HAWT operating at zero yaw angle and in a steady flow in a wind tunnel was measured using hot wire probes. By phase locked averaging and moving the probe axially and radially the full three dimensional mean flow file was determined. All measurements were within two chord lengths of the blades and at tip speed ratios giving high turbine power output, a condition approaching runaway, and a stalled condition. For all tip speed ratios the wakes were significantly three dimensional. Large velocity variations were associated with vortex structures in the wakes, and irrotational fluctuations caused by the blade bound circulation. The vorticity clearly defined the hub and tip vortices that traced helical paths downstream, with the constant tip vortex pitch inversely proportional to tip speed ratio. Close to the blades the flow was complicated, though vortex roll-up was completed within one chord length. Considerable changes in wake structure occurred with tip speed ratio. At high power output the wake showed tip and hub vortices connected by a diffuse vortex sheet of mostly radial vorticity from the blade boundary layers; blade bound circulation was almost constant. The structure approaching runaway was similar though the hub vortex was not well defined and formed a vortex sheet around the hub which lifted away and diffused. The stalled condition was more complicated, with evidence of incomplete tip and hub vortex formation. The stream-wise velocity of the tip vortex core decreased with increasing tip speed ratio, but this was never aligned with local streamlines. The core of the tip vortex was not circular but more elliptical. A phase locked averaged angular momentum analysis was undertaken, the extra terms introduced through phase locked averaging were small. (Abstract Truncated)

  13. Wake losses optimization of offshore wind farms with moveable floating wind turbines

    NARCIS (Netherlands)

    S.F. Rodrigues; R. Teixeira Pinto (Rodrigo); M. Soleimanzadeh (Maryam); P.A.N. Bosman (Peter); P. Bauer (Pavol)

    2015-01-01

    htmlabstractIn the future, floating wind turbines could be used to harvest energy in deep offshore areas where higher wind mean speeds are observed. Currently, several floating turbine concepts are being designed and tested in small scale projects; in particular, one concept allows the turbine to

  14. Short term prediction of the horizontal wind vector within a wake vortex warning system

    Energy Technology Data Exchange (ETDEWEB)

    Frech, M.; Holzaepfel, F.; Gerz, T. [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Wessling (Germany). Inst. fuer Physik der Atmosphaere; Konopka, J. [Deutsche Flugsicherung (DFS) GmbH, Langen (Germany)

    2000-07-14

    A wake vortex warning system (WVWS) has been developed for Frankfurt airport. This airport has two parallel runways which are separated by 518 m, a distance too short to operate them independently because wake vortices may be advected to the adjacent runway. The objective of the WVWS is to enable operation with reduced separation between two aircraft approaching the parallel runways at appropriate wind conditions. The WVWS applies a statistical persistence model to predict the crosswind within a 20 minute period. One of the main problems identified in the old WVWS are discontinuities between successive forecasts. These forecast breakdowns were not acceptable to airtraffic controllers. At least part of the problem was related to the fact that the forecast was solely based on the prediction of crosswind. A new method is developed on the basis of 523 days of sonic anemometer measurements at Frankfurt airport. It is demonstrated that the prediction of the horizontal wind vector avoids these difficulties and significantly improves the system's performance. (orig.)

  15. LiDAR Measurements of Full-scale Wind Turbine Wake Characteristics

    DEFF Research Database (Denmark)

    Hansen, Kurt Schaldemose; Larsen, Gunner Chr.; Mann, Jakob

    2009-01-01

    . The experimental setup, the amount of data, preliminary analysis and limitations of using LIDAR measurements to identify the wake dynamics will be presented. Resolving the wake in the meandering frame of reference further allows for identification of the wake characteristics both in terms of wake deficit and wake...

  16. A simple stationary semi-analytical wake model

    DEFF Research Database (Denmark)

    Larsen, Gunner Chr.

    We present an idealized simple, but fast, semi-analytical algorithm for computation of stationary wind farm wind fields with a possible potential within a multi-fidelity strategy for wind farm topology optimization. Basically, the model considers wakes as linear perturbations on the ambient non...... rotationally symmetric, and the rotor inflow fields are consistently assumed uniform. Expansion of stationary wake fields is believed to be significantly affected by meandering of wake deficits as e.g. described by the Dynamic Wake Meandering model. In the present context, this effect is approximately...... conditions are imposed), the present formulation of wake expansion is believed to underestimate wake expansion, because the analytical wake formulation dictates the wake expansion to behave as x1/3 with downstream distance, whereas wake expansion as primary controlled by wake meandering develops...

  17. Estimation of turbulence intensity using rotor effective wind speed in Lillgrund and Horns Rev-I offshore wind farms

    DEFF Research Database (Denmark)

    Gögmen, Tuhfe; Giebel, Gregor

    2016-01-01

    varies over the extent of the wind farm. This paper describes a method to estimate the TI at individual turbine locations by using the rotor effective wind speed calculated via high frequency turbine data. The method is applied to Lillgrund and Horns Rev-I offshore wind farms and the results are compared...... with TI derived from the meteorological mast, nacelle mounted anemometer on the turbines and estimation based on the standard deviation of power. The results show that the proposed TI estimation method is in the best agreement with the meteorological mast. Therefore, the rotor effective wind speed...... is shown to be applicable for the TI assessment in real-time wind farm calculations under different operational conditions. Furthermore, the TI in the wake is seen to follow the same trend with the estimated wake deficit which enables to quantify the turbulence in terms of the wake loss locally inside...

  18. Wind turbine wake interactions at field scale: An LES study of the SWiFT facility

    International Nuclear Information System (INIS)

    Yang, Xiaolei; Boomsma, Aaron; Sotiropoulos, Fotis; Barone, Matthew

    2014-01-01

    The University of Minnesota Virtual Wind Simulator (VWiS) code is employed to simulate turbine/atmosphere interactions in the Scaled Wind Farm Technology (SWiFT) facility developed by Sandia National Laboratories in Lubbock, TX, USA. The facility presently consists of three turbines and the simulations consider the case of wind blowing from South such that two turbines are in the free stream and the third turbine in the direct wake of one upstream turbine with separation of 5 rotor diameters. Large-eddy simulation (LES) on two successively finer grids is carried out to examine the sensitivity of the computed solutions to grid refinement. It is found that the details of the break-up of the tip vortices into small-scale turbulence structures can only be resolved on the finer grid. It is also shown that the power coefficient C P of the downwind turbine predicted on the coarse grid is somewhat higher than that obtained on the fine mesh. On the other hand, the rms (root-mean-square) of the C P fluctuations are nearly the same on both grids, although more small-scale turbulence structures are resolved upwind of the downwind turbine on the finer grid

  19. Comparison of wind turbine wake properties in non‐sheared inflow predicted by different computational fluid dynamics rotor models

    DEFF Research Database (Denmark)

    Troldborg, Niels; Zahle, Frederik; Réthoré, Pierre-Elouan

    2015-01-01

    The wake of the 5MW reference wind turbine designed by the National Renewable Energy Laboratory (NREL) is simulated using computational fluid dynamics with a fully resolved rotor geometry, an actuator line method and an actuator disc method, respectively. Simulations are carried out prescribing...

  20. Sandia Wake Imaging System Field Test Report: 2015 Deployment at the Scaled Wind Farm Technology (SWiFT) Facility.

    Energy Technology Data Exchange (ETDEWEB)

    Naughton, Brian Thomas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Herges, Thomas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-10-01

    This report presents the objectives, configuration, procedures, reporting , roles , and responsibilities and subsequent results for the field demonstration of the Sandia Wake Imaging System (SWIS) at the Sandia Scaled Wind Farm Technology (SWiFT) facility near Lubbock, Texas in June and July 2015.

  1. 3D Lagrangian VPM: simulations of the near-wake of an actuator disc and horizontal axis wind turbine

    DEFF Research Database (Denmark)

    Berdowski, T.; Ferreira, Célia Maria Dias; Walther, Jens Honore

    2016-01-01

    The application of a 3-dimensional Lagrangian vortex particle method has beenassessed for modelling the near-wake of an axisymmetrical actuator disc and 3-bladed horizontal axis wind turbine with prescribed circulation from the MEXICO (Model EXperiments InCOntrolled conditions) experiment...

  2. Effects of viscoelasticity in the high Reynolds number cylinder wake

    KAUST Repository

    Richter, David

    2012-01-16

    At Re = 3900, Newtonian flow past a circular cylinder exhibits a wake and detached shear layers which have transitioned to turbulence. It is the goal of the present study to investigate the effects which viscoelasticity has on this state and to identify the mechanisms responsible for wake stabilization. It is found through numerical simulations (employing the FENE-P rheological model) that viscoelasticity greatly reduces the amount of turbulence in the wake, reverting it back to a state which qualitatively appears similar to the Newtonian mode B instability which occurs at lower Re. By focusing on the separated shear layers, it is found that viscoelasticity suppresses the formation of the Kelvin-Helmholtz instability which dominates for Newtonian flows, consistent with previous studies of viscoelastic free shear layers. Through this shear layer stabilization, the viscoelastic far wake is then subject to the same instability mechanisms which dominate for Newtonian flows, but at far lower Reynolds numbers. © Copyright Cambridge University Press 2012.

  3. Shear layer approximation of Navier-Stokes steady equations for non-axisymmetric wind turbine wakes: Description, verification and first application

    Science.gov (United States)

    Trabucchi, Davide; Vollmer, Lukas; Kühn, Martin

    2016-09-01

    The number of turbines installed in offshore wind farms has strongly increased in the last years and at the same time the need for more precise estimation of the wind farm efficiency. For this reason, the wind energy community could benefit from more accurate models for multiple wakes. Existing engineering models can only simulate single wakes, which are superimposed if they are interacting in a wind farm. This method is a practical solution, but it is not fully supported by a physical background. The limitation to single wakes is given by the assumption that the wake is axisymmetric. As alternative, we propose a new shear model which is based on the existing engineering wake models, but is extended to simulate also non- axisymmetric wakes. In this paper, we present the theoretical background of the model and two application cases. First, we proved that for axisymmetric wakes the new model is equivalent to a commonly used engineering model. Then, we evaluated the improvements of the new model for the simulation of a non-axisymmetric wake using a large eddy simulation as reference. The results encourage the further development of the model, and promise a successful application for the simulation of multiple wakes.

  4. The Long distance wake behind Horns Rev I studied using large eddy simulations and a wind turbine parameterization in WRF

    Science.gov (United States)

    Eriksson, O.; Baltscheffsky, M.; Breton, S.-P.; Söderberg, S.; Ivanell, S.

    2017-05-01

    The aim of the present paper is to obtain a better understanding of long distance wakes generated by wind farms as a first step towards a better understanding of farm to farm interaction. The Horns Rev I (HR) wind farm is considered for this purpose, where comparisons are performed between microscale Large Eddy Simulations (LES) using an Actuator Disc model (ACD), mesoscale simulations in the Weather Research and Forecasting Model (WRF) using a wind turbine parameterization, production data as well as wind measurements in the wind farm wake. The LES is manually set up according to the wind conditions obtained from the mesoscale simulation as a first step towards a meso/microscale coupling. The LES using an ACD are performed in the EllipSys3D code. A forced boundary layer (FBL) approach is used to introduce the desired wind shear and the atmospheric turbulence field from the Mann model. The WRF uses a wind turbine parameterization based on momentum sink. To make comparisons with the LESs and the site data possible an idealized setup of WRF is used in this study. The case studied here considers a westerly wind direction sector (at hub height) of 270 ± 2.5 degrees and a wind speed of 8 ± 0.5 m/s. For both the simulations and the site data a neutral atmosphere is considered. The simulation results for the relative production as well as the wind speed 2 km and 6 km downstream from the wind farm are compared to site data. Further comparisons between LES and WRF are also performed regarding the wake recovery and expansion. The results are also compared to an earlier study of HR using LES as well as an earlier comparison of LES and WRF. Overall the results in this study show a better agreement between LES and WRF as well as better agreement between simulations and site data. The procedure of using the profile from WRF as inlet to LES can be seen as a simplified coupling of the models that could be developed further to combine the methods for cases of farm to farm

  5. Reynolds number effects on the performance and near-wake of a cross-flow turbine

    Science.gov (United States)

    Bachant, Peter; Wosnik, Martin

    2013-11-01

    To design wind or marine hydrokinetic (MHK) turbine farms with high efficiency, interactions between turbine wakes must be accurately predicted. However, to date numerical models predicting detailed wake properties of cross-flow (or vertical-axis) turbines have been validated with experimental data taken at Reynolds numbers significantly lower than those of full scale devices, casting doubt on the models' accuracy. To address this uncertainty, we investigated the effects of Reynolds number on the performance and near-wake characteristics of a 3-bladed cross-flow turbine, both experimentally and numerically. Mechanical power output and overall streamwise drag were measured in a towing tank at turbine diameter Reynolds numbers ReD = 0 . 5 ×105 - 2 . 0 ×106 . A detailed map of the near-wake one turbine diameter downstream was acquired via acoustic Doppler velocimetry for each Reynolds number case, from which differences in the mean velocity, turbulence intensity, and Reynolds stresses are highlighted. Finally, Reynolds-averaged Navier-Stokes (RANS) numerical simulations were performed, the results from which are compared with the experimental data. Work supported by NSF-CBET grant 1150797.

  6. Extraction of the wake induction and angle of attack on rotating wind turbine blades from PIV and CFD results

    Directory of Open Access Journals (Sweden)

    I. Herráez

    2018-01-01

    Full Text Available The analysis of wind turbine aerodynamics requires accurate information about the axial and tangential wake induction as well as the local angle of attack along the blades. In this work we present a new method for obtaining them conveniently from the velocity field. We apply the method to the New Mexico particle image velocimetry (PIV data set and to computational fluid dynamics (CFD simulations of the same turbine. This allows the comparison of experimental and numerical results of the mentioned quantities on a rotating wind turbine. The presented results open up new possibilities for the validation of numerical rotor models.

  7. The Effect of Wake Passing on Turbine Blade Film Cooling

    Science.gov (United States)

    Heidmann, James David

    1996-01-01

    The effect of upstream blade row wake passing on the showerhead film cooling performance of a downstream turbine blade has been investigated through a combination of experimental and computational studies. The experiments were performed in a steady-flow annular turbine cascade facility equipped with an upstream rotating row of cylindrical rods to produce a periodic wake field similar to that found in an actual turbine. Spanwise, chordwise, and temporal resolution of the blade surface temperature were achieved through the use of an array of nickel thin-film surface gauges covering one unit cell of showerhead film hole pattern. Film effectiveness and Nusselt number values were determined for a test matrix of various injectants, injectant blowing ratios, and wake Strouhal numbers. Results indicated a demonstratable reduction in film effectiveness with increasing Strouhal number, as well as the expected increase in film effectiveness with blowing ratio. An equation was developed to correlate the span-average film effectiveness data. The primary effect of wake unsteadiness was found to be correlated well by a chordwise-constant decrement of 0.094-St. Measurable spanwise film effectiveness variations were found near the showerhead region, but meaningful unsteady variations and downstream spanwise variations were not found. Nusselt numbers were less sensitive to wake and injection changes. Computations were performed using a three-dimensional turbulent Navier-Stokes code which was modified to model wake passing and film cooling. Unsteady computations were found to agree well with steady computations provided the proper time-average blowing ratio and pressure/suction surface flow split are matched. The remaining differences were isolated to be due to the enhanced mixing in the unsteady solution caused by the wake sweeping normally on the pressure surface. Steady computations were found to be in excellent agreement with experimental Nusselt numbers, but to overpredict

  8. Anisotropy of the Reynolds stress tensor in the wakes of wind turbine arrays in Cartesian arrangements with counter-rotating rotors

    Science.gov (United States)

    Hamilton, Nicholas; Cal, Raúl Bayoán

    2015-01-01

    A 4 × 3 wind turbine array in a Cartesian arrangement was constructed in a wind tunnel setting with four configurations based on the rotational sense of the rotor blades. The fourth row of devices is considered to be in the fully developed turbine canopy for a Cartesian arrangement. Measurements of the flow field were made with stereo particle-image velocimetry immediately upstream and downstream of the selected model turbines. Rotational sense of the turbine blades is evident in the mean spanwise velocity W and the Reynolds shear stress - v w ¯ . The flux of kinetic energy is shown to be of greater magnitude following turbines in arrays where direction of rotation of the blades varies. Invariants of the normalized Reynolds stress anisotropy tensor (η and ξ) are plotted in the Lumley triangle and indicate that distinct characters of turbulence exist in regions of the wake following the nacelle and the rotor blade tips. Eigendecomposition of the tensor yields principle components and corresponding coordinate system transformations. Characteristic spheroids representing the balance of components in the normalized anisotropy tensor are composed with the eigenvalues yielding shapes predicted by the Lumley triangle. Rotation of the coordinate system defined by the eigenvectors demonstrates trends in the streamwise coordinate following the rotors, especially trailing the top-tip of the rotor and below the hub. Direction of rotation of rotor blades is shown by the orientation of characteristic spheroids according to principle axes. In the inflows of exit row turbines, the normalized Reynolds stress anisotropy tensor shows cumulative effects of the upstream turbines, tending toward prolate shapes for uniform rotational sense, oblate spheroids for streamwise organization of rotational senses, and a mixture of characteristic shapes when the rotation varies by row. Comparison between the invariants of the Reynolds stress anisotropy tensor and terms from the mean

  9. PIV and Hotwire Measurement and Analysis of Tip Vortices and Turbulent Wake Generated by a Model Horizontal Axis Wind Turbine

    Science.gov (United States)

    Green, D.; Tan, Y. M.; Chamorro, L. P.; Arndt, R.; Sotiropoulos, F.; Sheng, J.

    2011-12-01

    Understanding vortical flow structures and turbulence in the wake flow behind a Horizontal Axis Wind Turbine (HAWT) has widespread applications in efficient blade design. Moreover, the knowledge of wake-turbine interactions allows us to devise optimal operational parameters, such as the spatial allocation and control algorithms of wind turbines, for a densely populated wind farm. To understand the influence of tip vortices on energy containing mean flow and turbulence, characteristics of vortical structures and turbulence must be quantified thoroughly. In this study, we conduct phase-locked Particle Image Velocimetry (PIV) measurements of the flow before and after a model HAWT, which is located in a zero-pressure gradient wind tunnel with a cross section of 1.7 × 1.7 m and a test section of 16 m in length. A three-blade model HAWT with a diameter of 605 mm and tip-speed ratio of 5 is used. PIV images are recorded by a 2048 × 2048 CCD camera and streamed at 6 Hz continuously; and phased locked with the passage of the blade at its vertical position. Each PIV measurement covers a 0.13 × 0.13 m2 sample area with the spatial resolution of 63 μm and a vector spacing of 0.5 mm. All experiments are conducted at the free-stream wind speed of 10 m/s. Flow fields at thirty consecutive downstream locations up to six rotor diameters and 144 mid chord lengths are measured. At each location, we obtain at least 10,000 instantaneous PIV realizations or 20,000 images. Three different configurations: single, dual, and trio turbines located at 5 rotor diameter upstream to each other, are examined experimentally. The flow statistics include mean wake velocity distributions, characteristics of tip vortices evolving downstream, fluctuation velocity, turbulent kinetic energy, stresses, and energy spectra. We find that tip vortices decay much faster in the wake of the upstream turbines (multiple-turbine configurations), whereas they maintain the coherence and strength behind a single

  10. Effects of Aircraft Wake Dynamics on Measured and Simulated NO(x) and HO(x) Wake Chemistry. Appendix B

    Science.gov (United States)

    Lewellen, D. C.; Lewellen, W. S.

    2001-01-01

    High-resolution numerical large-eddy simulations of the near wake of a B757 including simplified NOx and HOx chemistry were performed to explore the effects of dynamics on chemistry in wakes of ages from a few seconds to several minutes. Dilution plays an important basic role in the NOx-O3 chemistry in the wake, while a more interesting interaction between the chemistry and dynamics occurs for the HOx species. These simulation results are compared with published measurements of OH and HO2 within a B757 wake under cruise conditions in the upper troposphere taken during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) mission in May 1996. The simulation provides a much finer grained representation of the chemistry and dynamics of the early wake than is possible from the 1 s data samples taken in situ. The comparison suggests that the previously reported discrepancy of up to a factor of 20 - 50 between the SUCCESS measurements of the [HO2]/[OH] ratio and that predicted by simplified theoretical computations is due to the combined effects of large mixing rates around the wake plume edges and averaging over volumes containing large species fluctuations. The results demonstrate the feasibility of using three-dimensional unsteady large-eddy simulations with coupled chemistry to study such phenomena.

  11. PIV and LDA measurements of the wake behind a wind turbine model

    DEFF Research Database (Denmark)

    Naumov, I. V.; Mikkelsen, Robert Flemming; Okulov, Valery

    2014-01-01

    to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different...

  12. Aeroelastic impact of above-rated wave-induced structural motions on the near-wake stability of a floating offshore wind turbine rotor

    Science.gov (United States)

    Rodriguez, Steven; Jaworski, Justin

    2017-11-01

    The impact of above-rated wave-induced motions on the stability of floating offshore wind turbine near-wakes is studied numerically. The rotor near-wake is generated using a lifting-line free vortex wake method, which is strongly coupled to a finite element solver for kinematically nonlinear blade deformations. A synthetic time series of relatively high-amplitude/high-frequency representative of above-rated conditions of the NREL 5MW referece wind turbine is imposed on the rotor structure. To evaluate the impact of these above-rated conditions, a linear stability analysis is first performed on the near wake generated by a fixed-tower wind turbine configuration at above-rated inflow conditions. The platform motion is then introduced via synthetic time series, and a stability analysis is performed on the wake generated by the floating offshore wind turbine at the same above-rated inflow conditions. The stability trends (disturbance modes versus the divergence rate of vortex structures) of the two analyses are compared to identify the impact that above-rated wave-induced structural motions have on the stability of the floating offshore wind turbine wake.

  13. Wake-field generation by the ponderomotive memory effect

    International Nuclear Information System (INIS)

    Wolf, U.; Schamel, H.

    1997-01-01

    An analytical and numerical investigation of the plasma response to an imposed high frequency wave packet with a slow explicit time-dependent envelope is presented. An underlying picture of ponderomotive effects is developed, which shows that the explicit time dependence forces us to treat the problem kinetically, and furthermore, that a wake field is generated by the ponderomotive memory effect. The latter supplements the well-known ponderomotive force and fake heating effect. Several perturbation schemes are compared showing that the influence of resonant particles, treated by the method of characteristics, has to be taken into account for Langmuir wave packets with kλ d ≥0.2, where k is the wave number and λ d the Debye length. A self-consistent Vlasov simulation shows the disappearance of the density depression in the case of immobile ions, whereas the wake-field pattern survives self-consistency. copyright 1997 The American Physical Society

  14. Validation of four LES and a vortex model against stereo-PIV measurements in the near wake of an actuator disc and a wind turbine

    DEFF Research Database (Denmark)

    Lignarolo, Lorenzo E.M.; Mehta, Dhruv; Stevens, Richard J.A.M.

    2016-01-01

    In this paper we report the results of a workshop organised by the Delft University of Technology in 2014, aiming at the comparison between different state-of-the-art numerical models for the simulation of wind turbine wakes. The chosen benchmark case is a wind tunnel measurement, where stereosco...

  15. A Large-Eddy Simulation Study of Vertical Axis Wind Turbine Wakes in the Atmospheric Boundary Layer

    Directory of Open Access Journals (Sweden)

    Sina Shamsoddin

    2016-05-01

    Full Text Available In a future sustainable energy vision, in which diversified conversion of renewable energies is essential, vertical axis wind turbines (VAWTs exhibit some potential as a reliable means of wind energy extraction alongside conventional horizontal axis wind turbines (HAWTs. Nevertheless, there is currently a relative shortage of scientific, academic and technical investigations of VAWTs as compared to HAWTs. Having this in mind, in this work, we aim to, for the first time, study the wake of a single VAWT placed in the atmospheric boundary layer using large-eddy simulation (LES. To do this, we use a previously-validated LES framework in which an actuator line model (ALM is incorporated. First, for a typical three- and straight-bladed 1-MW VAWT design, the variation of the power coefficient with both the chord length of the blades and the tip-speed ratio is analyzed by performing 117 simulations using LES-ALM. The optimum combination of solidity (defined as N c / R , where N is the number of blades, c is the chord length and R is the rotor radius and tip-speed ratio is found to be 0.18 and 4.5, respectively. Subsequently, the wake of a VAWT with these optimum specifications is thoroughly examined by showing different relevant mean and turbulence wake flow statistics. It is found that for this case, the maximum velocity deficit at the equator height of the turbine occurs 2.7 rotor diameters downstream of the center of the turbine, and only after that point, the wake starts to recover. Moreover, it is observed that the maximum turbulence intensity (TI at the equator height of the turbine occurs at a distance of about 3.8 rotor diameters downstream of the turbine. As we move towards the upper and lower edges of the turbine, the maximum TI (at a certain height increases, and its location moves relatively closer to the turbine. Furthermore, whereas both TI and turbulent momentum flux fields show clear vertical asymmetries (with larger magnitudes at the

  16. Typhoon Effect on Kuroshio and Green Island Wakes: A Modelling Study

    Directory of Open Access Journals (Sweden)

    Tai-Wen Hsu

    2018-01-01

    Full Text Available Green Island, located in the typhoon-active eastern Taiwan coastal water, is the potential Kuroshio power plant site. In this study, a high resolution (250–2250 m shallow-water equations model is used to investigate the effect of typhoon on the hydro-dynamics of Kuroshio and Green Island wakes. Two typhoon–Kuroshio interactions—typhoon Soulik and Holland’s typhoon model—are studied. Simulation results of typhoon Soulik indicate salient characteristics of Kuroshio, and downstream island wakes seems less affected by the typhoon Soulik, because the shortest distance of typhoon Soulik is 250 km away from Green Island and wind speed near Green Island is small. Moreover, Kuroshio currents increase when flow is in the same direction as the counterclockwise rotation of typhoon, and vice versa. This finding is in favorable agreement with the TOROS (Taiwan Ocean Radar Observing System observed data. Simulations of Kuroshio and Holland’s typhoon model successfully reproduces the downstream recirculation and vortex street. Numerical results reveal that the slow moving typhoon has a more significant impact on the Kuroshio and downstream Green Island wakes than the fast moving typhoon does. The rightward bias phenomenon is evident—Kuroshio currents increase (decrease in the right (left of the moving typhoon’s track, due to the counterclockwise rotation of typhoon.

  17. Status of wake and array loss research

    Energy Technology Data Exchange (ETDEWEB)

    Elliott, D.L.

    1991-09-01

    In recent years, many projects have evaluated wind turbine wake effects and resultant array losses in both Europe and the United States. This paper examines the status of current knowledge about wake effects and array losses and suggests future research. Single-turbine wake characteristics have been studied extensively and are generally described well by existing theoretical models. Field measurements of wake effects in wind turbine arrays are largely limited to small arrays, with 2 to 4 rows of turbines. Few data have been published on wake effects within large arrays. Measurements of wake deficits downwind of large arrays that deficits are substantially larger and extend farther downwind than expected. Although array design models have been developed, these models have been tested and verified using only limited data from a few rows of wind turbines in complex terrain, whereas some of the largest arrays have more than 40 rows of wind turbines. Planned cooperative efforts with the wind industry will obtain existing data relevant to analyzing energy deficits within large arrays and identifying data sets for potential use in array model verification efforts. Future research being considered include a cooperative research experiment to obtain more definitive data on wake deficits and turbulence within and downwind of large arrays. 16 refs., 9 figs., 1 tab.

  18. Wake modeling and simulation

    DEFF Research Database (Denmark)

    Larsen, Gunner Chr.; Madsen Aagaard, Helge; Larsen, Torben J.

    We present a consistent, physically based theory for the wake meandering phenomenon, which we consider of crucial importance for the overall description of wind turbine loadings in wind farms. In its present version the model is confined to single wake situations. The model philosophy does, howev...... methodology has been implemented in the aeroelastic code HAWC2, and example simulations of wake situations, from the small Tjæreborg wind farm, have been performed showing satisfactory agreement between predictions and measurements...

  19. Velocity-intermittency structure for wake flow of the pitched single wind turbine under different inflow conditions

    Science.gov (United States)

    Crist, Ryan; Cal, Raul Bayoan; Ali, Naseem; Rockel, Stanislav; Peinke, Joachim; Hoelling, Michael

    2017-11-01

    The velocity-intermittency quadrant method is used to characterize the flow structure of the wake flow in the boundary layer of a wind turbine array. Multifractal framework presents the intermittency as a pointwise Hölder exponent. A 3×3 wind turbine array tested experimentally provided a velocity signal at a 21×9 downstream location, measured via hot-wire anemometry. The results show a negative correlation between the velocity and the intermittency at the hub height and bottom tip, whereas the top tip regions show a positive correlation. Sweep and ejection based on the velocity and intermittency are dominant downstream from the rotor. The pointwise results reflect large-scale organization of the flow and velocity-intermittency events corresponding to a foreshortened recirculation region near the hub height and the bottom tip.

  20. Wind Speed Estimation and Parametrization of Wake Models for Downregulated Offshore Wind Farms within the scope of PossPOW Project

    DEFF Research Database (Denmark)

    Göçmen Bozkurt, Tuhfe; Giebel, Gregor; Poulsen, Niels Kjølstad

    2014-01-01

    With increasing installed capacity, wind farms are requested to downregulate more frequently, especially in the offshore environment. Determination and verification of possible (or available) power of downregulated offshore wind farms are the aims of the PossPOW project (see PossPOW.dtu.dk). Two ...... period. The re-calibrated model has to be further parametrized to include dynamic effects such as wind direction variability and meandering also considering different averaging time scales before implemented in full scale wind farms....

  1. Benchmarking of wind farm scale wake models in the EERA - DTOC project

    DEFF Research Database (Denmark)

    Réthoré, Pierre-Elouan; Hansen, Kurt Schaldemose; Barthelmie, R.J.

    2013-01-01

    Designing offshore wind farms next to existing or planned wind farm clusters has recently become a common practice in the North Sea. These types of projects face unprecedented challenges in term of wind energy siting. The currently ongoing European project FP7 EERA - DTOC (Design Tool for Offshor...

  2. Collection System Cable Routing and Wake Losses Optimization in Offshore Wind Farms

    NARCIS (Netherlands)

    Fragoso Rodrigues, S.M.; Bauer, P.; Bosman, P.A.N.; Pierik, J.

    2014-01-01

    Offshore wind farms with high installed capacities and located further from the shore are starting to be built by northern European countries. Furthermore, it is expected that by 2020, several dozens of large offshore wind farms will be built in the Baltic, Irish and North seas. These wind farms

  3. Determination of Wind Turbine Near-Wake Length Based on Stability Analysis

    DEFF Research Database (Denmark)

    Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming; Sarmast, Sasan

    2014-01-01

    of the study it is found that the amplification of specific waves (traveling structures) along the tip vortex spirals is responsible for triggering the instability leading to wake breakdown. The presence of unstable modes in the wake is related to the mutual inductance (vortex pairing) instability where...... there is an out-of-phase displacement of successive helix turns. Furthermore, using the non-dimensional growth rate, it is found that the pairing instability has a universal growth rate equal to π/2. Using this relationship, and the assumption that breakdown to turbulence occurs once a vortex has experienced...

  4. Evolution and breakdown of helical vortex wakes behind a wind turbine

    International Nuclear Information System (INIS)

    Nemes, A; Jacono, D Lo; Sheridan, J; Blackburn, H M; Sherry, M

    2014-01-01

    The wake behind a three-bladed Glauert model rotor in a water channel was investigated. Planar particle image velocimetry was used to measure the velocity fields on the wake centre-line, with snapshots phase-locked to blade position of the rotor. Phase- locked averages of the velocity and vorticity fields are shown, with tip vortex interaction and entanglement of the helical filaments elucidated. Proper orthogonal decomposition and topology-based vortex identification are used to filter the PIV images for coherent structures and locate vortex cores. Application of these methods to the instantaneous data reveals unsteady behaviour of the helical filaments that is statistically quantifiable

  5. Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw

    Directory of Open Access Journals (Sweden)

    Moutaz Elgammi

    2016-06-01

    Full Text Available Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and the development of a skewed vortical wake created downstream of the rotor plane. Blade surface pressure measurements conducted on the NREL Phase VI rotor in yawed conditions have shown that dynamic stall causes the wind turbine blades to experience significant cycle-to-cycle variations in aerodynamic loading. These effects were observed even though the rotor was subjected to a fixed speed and a uniform and steady wind flow. This phenomenon is not normally predicted by existing dynamic stall models integrated in wind turbine design codes. This paper couples blade pressure measurements from the NREL Phase VI rotor to a free-wake vortex model to derive the angle of attack time series at the different blade sections over multiple rotor rotations and three different yaw angles. Through the adopted approach it was possible to investigate how the rotor self-induced aerodynamic load fluctuations influence the unsteady variations in the blade angles of attack and induced velocities. The hysteresis loops for the normal and tangential load coefficients plotted against the angle of attack were plotted over multiple rotor revolutions. Although cycle-to-cycle variations in the angles of attack at the different blade radial locations and azimuth positions are found to be relatively small, the corresponding variations in the normal and tangential load coefficients may be significant. Following a statistical analysis, it was concluded that the load coefficients follow a normal distribution at the majority of blade azimuth angles and radial locations. The results of this study provide further insight on how existing engineering models for dynamic stall may be improved through

  6. Modelling lidar volume-averaging and its significance to wind turbine wake measurements

    DEFF Research Database (Denmark)

    Meyer Forsting, Alexander Raul; Troldborg, Niels; Borraccino, Antoine

    2017-01-01

    gradients, like the rotor wake, can it be detrimental. Hence, an efficient algorithm mimicking lidar flow sampling is presented, which considers both pulsed and continous-wave lidar weighting functions. The flow-field around a 2.3 MW turbine is simulated using Detached Eddy Simulation in combination...

  7. Calculation of depleted wind resources near wind farms

    DEFF Research Database (Denmark)

    Nielsen, Morten

    2015-01-01

    Traditional wind resource maps include wind distribution, energy density and potential power production without wake effects. Adding wake effect to such maps is feasible by means of a new method based on Fourier transformation,and the extra computational work is comparable to that of the basic wind...... resource map. The method is mainly intended for mapping inter-farm wake effects. It will work for all linear wake models and may even be extended to complex terrain by certain simplifying assumptions. The method is implemented for the Park model and Fuga models. A test example shows that these models...

  8. Simulating Wake Vortex Detection with the Sensivu Doppler Wind Lidar Simulator

    Science.gov (United States)

    Ramsey, Dan; Nguyen, Chi

    2014-01-01

    In support of NASA's Atmospheric Environment Safety Technologies NRA research topic on Wake Vortex Hazard Investigation, Aerospace Innovations (AI) investigated a set of techniques for detecting wake vortex hazards from arbitrary viewing angles, including axial perspectives. This technical report describes an approach to this problem and presents results from its implementation in a virtual lidar simulator developed at AI. Threedimensional data volumes from NASA's Terminal Area Simulation System (TASS) containing strong turbulent vortices were used as the atmospheric domain for these studies, in addition to an analytical vortex model in 3-D space. By incorporating a third-party radiative transfer code (BACKSCAT 4), user-defined aerosol layers can be incorporated into atmospheric models, simulating attenuation and backscatter in different environmental conditions and altitudes. A hazard detection algorithm is described that uses a twocomponent spectral model to identify vortex signatures observable from arbitrary angles.

  9. Fatigue reliability and effective turbulence models in wind farms

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard; Frandsen, Sten Tronæs; Tarp-Johansen, N.J.

    2007-01-01

    Offshore wind farms with 100 or more wind turbines are expected to be installed many places during the next years. Behind a wind turbine a wake is formed where the mean wind speed decreases slightly and the turbulence intensity increases significantly. This increase in turbulence intensity in wak...

  10. Collection Network Cable Routing and Wake Losses Optimization in Offshore Wind Farms

    NARCIS (Netherlands)

    S.F. Rodrigues; P. Bauer (Pavol); P.A.N. Bosman (Peter); J. Pierik

    2014-01-01

    htmlabstractOffshore wind farms with high installed capacities and located further from the shore are starting to be built by northern European countries. Furthermore, it is expected that by 2020, several dozens of large offshore wind farms will be built in the Baltic, Irish and North seas. These

  11. A classical model wind turbine wake “blind test” revisited by remote sensing lidars

    DEFF Research Database (Denmark)

    Sjöholm, Mikael; Angelou, Nikolas; Nielsen, Morten Busk

    2017-01-01

    the auspices of the IRPWind initiative within the community of the European Energy Research Alliance (EERA) Joint Programme on Wind Energy. The wind tunnel has a test section that is 11 m long and a cross-section of 2 by 3 m with windows along one side of the tunnel allowing for optical access from outside...

  12. Test Plan for the Wake Steering Experiment at the Scaled Wind Farm Technology (SWiFT) Facility.

    Energy Technology Data Exchange (ETDEWEB)

    Naughton, Brian Thomas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-02-01

    This document is a test plan describing the objectives, configuration, procedures, reporting, roles, and responsibilities for conducting the joint Sandia National Laboratories and National Renewable Energy Laboratory Wake Steering Experiment at the Sandia Scaled Wind Farm Technology (SWiFT) facility near Lubbock, Texas in 2016 and 2017 . The purpose of this document is to ensure the test objectives and procedures are sufficiently detailed such that al l involved personnel are able to contribute to the technical success of the test. This document is not intended to address safety explicitly which is addressed in a separate document listed in the references titled Sandia SWiFT Facility Site Operations Manual . Both documents should be reviewed by all test personnel.

  13. A wind turbine hybrid simulation framework considering aeroelastic effects

    Science.gov (United States)

    Song, Wei; Su, Weihua

    2015-04-01

    In performing an effective structural analysis for wind turbine, the simulation of turbine aerodynamic loads is of great importance. The interaction between the wake flow and the blades may impact turbine blades loading condition, energy yield and operational behavior. Direct experimental measurement of wind flow field and wind profiles around wind turbines is very helpful to support the wind turbine design. However, with the growth of the size of wind turbines for higher energy output, it is not convenient to obtain all the desired data in wind-tunnel and field tests. In this paper, firstly the modeling of dynamic responses of large-span wind turbine blades will consider nonlinear aeroelastic effects. A strain-based geometrically nonlinear beam formulation will be used for the basic structural dynamic modeling, which will be coupled with unsteady aerodynamic equations and rigid-body rotations of the rotor. Full wind turbines can be modeled by using the multi-connected beams. Then, a hybrid simulation experimental framework is proposed to potentially address this issue. The aerodynamic-dominant components, such as the turbine blades and rotor, are simulated as numerical components using the nonlinear aeroelastic model; while the turbine tower, where the collapse of failure may occur under high level of wind load, is simulated separately as the physical component. With the proposed framework, dynamic behavior of NREL's 5MW wind turbine blades will be studied and correlated with available numerical data. The current work will be the basis of the authors' further studies on flow control and hazard mitigation on wind turbine blades and towers.

  14. Progressive Loss of the Orexin Neurons Reveals Dual Effects on Wakefulness

    Science.gov (United States)

    Branch, Abigail F.; Navidi, William; Tabuchi, Sawako; Terao, Akira; Yamanaka, Akihiro; Scammell, Thomas E.; Diniz Behn, Cecilia

    2016-01-01

    Study Objectives: Narcolepsy is caused by loss of the orexin (also known as hypocretin) neurons. In addition to the orexin peptides, these neurons release additional neurotransmitters, which may produce complex effects on sleep/wake behavior. Currently, it remains unknown whether the orexin neurons promote the initiation as well as the maintenance of wakefulness, and whether the orexin neurons influence initiation or maintenance of sleep. To determine the effects of the orexin neurons on the dynamics of sleep/wake behavior, we analyzed sleep/wake architecture in a novel mouse model of acute orexin neuron loss. Methods: We used survival analysis and other statistical methods to analyze sleep/wake architecture in orexin-tTA ; TetO diphtheria toxin A mice at different stages of orexin neuron degeneration. Results: Progressive loss of the orexin neurons dramatically reduced survival of long wake bouts, but it also improved survival of brief wake bouts. In addition, with loss of the orexin neurons, mice were more likely to wake during the first 30 sec of nonrapid eye movement sleep and then less likely to return to sleep during the first 60 sec of wakefulness. Conclusions: These findings help explain the sleepiness and fragmented sleep that are characteristic of narcolepsy. Orexin neuron loss impairs survival of long wake bouts resulting in poor maintenance of wakefulness, but this neuronal loss also fragments sleep by increasing the risk of awakening at the beginning of sleep and then reducing the likelihood of quickly returning to sleep. Citation: Branch AF, Navidi W, Tabuchi S, Terao A, Yamanaka A, Scammell TE, Diniz Behn C. Progressive loss of the orexin neurons reveals dual effects on wakefulness. SLEEP 2016;39(2):369–377. PMID:26446125

  15. Stability Impact on Wake Development in Moderately Complex Terrain

    Science.gov (United States)

    Infield, D.; Zorzi, G.

    2017-05-01

    This paper uses a year of SCADA data from Whitelee Wind Farm near Glasgow to investigate wind turbine wake development in moderately complex terrain. Atmospheric stability measurements in terms of Richardson number from a met mast at an adjoining site have been obtained and used to assess the impact of stability on wake development. Considerable filtering of these data has been undertaken to ensure that all turbines are working normally and are well aligned with the wind direction. A group of six wind turbines, more or less in a line, have been selected for analysis, and winds within a 2 degree direction sector about this line are used to ensure, as far as possible, that all the turbines investigated are fully immersed in the wake/s of the upstream turbine/s. Results show how the terrain effects combine with the wake effects, with both being of comparable importance for the site in question. Comparison has been made with results from two commercial CFD codes for neutral stability, and reasonable agreement is demonstrated. Richardson number has been plotted against wind shear and turbulence intensity at a met mast on the wind farm that for the selected wind direction is not in the wake of any turbines. Good correlations are found indicating that the Richardson numbers obtained are reliable. The filtered data used for wake analysis were split according to Richardson number into two groups representing slightly stable to neutral, and unstable conditions. Very little difference in wake development is apparent. A greater difference can be observed when the data are separated simply by turbulence intensity, suggesting that, although turbulence intensity is correlated with stability, of the two it is the parameter that most directly impacts on wake development through mixing of ambient and wake flows.

  16. CFD Study on Effective Wake of Conventional and Tip-modified Propellers

    DEFF Research Database (Denmark)

    Shin, K. W.; Andersen, Poul

    2016-01-01

    -propulsion tests. The effects of different Reynolds number on higher effective wake fraction of tip-modified propellers are investigated by open-water simulations with varying the propeller speed and evaluations of effective wake extracted from self-propulsion simulations on tip-modified and conventional...... propellers. Open-water simulations show that the advance ratio at the design thrust is higher at a higher Reynolds number for both propellers and the advance ratio increase is smaller for the tip-modified propeller, which results in a higher effective wake fraction. Effective wake fractions are evaluated...... by integrating velocity fields at a section 40% of the propeller radius upstream from the propeller plane in self-propulsion simulations. The difference of effective wake fraction from integrating velocity fields between tip-modified and conventional propellers is less than 1%. Based on the open-water simulation...

  17. Optimization of Wind Farm Layout in Complex Terrain

    DEFF Research Database (Denmark)

    Xu, Chang; Yang, Jianchuan; Li, Chenqi

    2013-01-01

    distribution law and wake loss between different turbines into consideration and calculated the sheltering area effect of wake loss from upstream wind turbines on downstream wind turbines. Wind direction was divided into sixteen sections, and the wind speed was processed by the Weibull distribution....... To calculate the output of each section, we used the wind speed distribution and its probability density as well as the wake loss between wind turbines for every section. The objective function is maximization of the whole wind farm's power output and the free variables are the wind turbines' coordinates which...

  18. Effect of prolonged wakefulness on electroencephalographic oscillatory activity during sleep.

    Science.gov (United States)

    Olbrich, Eckehard; Landolt, Hans Peter; Achermann, Peter

    2014-06-01

    The human sleep electroencephalogram (EEG) is characterized by the occurrence of distinct oscillatory events such as delta waves, sleep spindles and alpha activity. We applied a previously proposed algorithm for the detection of such events and investigated their incidence and frequency in baseline and recovery sleep after 40 h of sustained wakefulness in 27 healthy young subjects. The changes in oscillatory events induced by sleep deprivation were compared to the corresponding spectral changes. Both approaches revealed, on average, an increase in low frequency activity and a decrease in spindle activity after sleep deprivation. However, the increase of oscillatory events in the delta range and decrease in the sigma range occurred in a more restricted frequency range compared to spectral changes. The mean relative power spectra showed a significant increase in theta and alpha activity after sleep deprivation while, on average, the event analysis showed only a weak effect in the theta band. The reason for this discrepancy is that the spectral analysis does not distinguish between diffuse activity and clearly visible temporally localized oscillations, while the event analysis would detect only the latter. Additionally, only a few individuals clearly showed activity in the theta or alpha frequency bands. Conversely, event analysis revealed that some individuals showed an increased rate of sleep spindles after sleep deprivation, a fact that was not evident in the relative power spectra due to a decrease in background activity. The two methods complement each other and facilitate the interpretation of distinct changes induced by prolonged wakefulness in sleep EEG. © 2013 European Sleep Research Society.

  19. Numerical analysis of the scale effect of the nominal wake field of KCS

    Directory of Open Access Journals (Sweden)

    ZHANG Haipeng

    2017-01-01

    Full Text Available In order to study the scale effect of the nominal wake field, the viscous flow field of KCS is studied without considering the free surface effect, and the nominal wake fields of KCS at different scales including full scale are solved numerically using the RANS method and the SST k-ω turbulence model. By comprehensively comparing the computed results with experimental data, the scale effect of the nominal wake field is further investigated. This shows that the reciprocal of the mean axial wake fraction at each radius exhibits a near-linear dependence on the Reynolds number in a logarithmic scale; for the nominal wake field of the propeller disc of KCS without a propeller, two wake peaks exit, and the amplitude of the axial wake peak decreases with the increase of the Reynolds number, which is conducive to a decrease in propeller exciting force and propeller cavitation; the scale effect of the small scale model is more obvious, and the scale effect of the mean axial wake fraction in the inner area is stronger than it is in the outer area.

  20. Scanning Lidar Spatial Calibration and Alignment Method for Wind Turbine Wake Characterization

    DEFF Research Database (Denmark)

    Herges, Thomas; Maniaci, David; Naughton, Brian

    2017-01-01

    Sandia National Laboratories and the National Renewable Energy Laboratory conducted a field campaign at the Scaled Wind Farm Technology (SWiFT) Facility using a customized scanning lidar from the Technical University of Denmark. The results from this field campaign will support the validation...

  1. Predicting wind farm wake interaction with RANS: an investigation of the Coriolis force

    DEFF Research Database (Denmark)

    van der Laan, Paul; Hansen, Kurt Schaldemose; Sørensen, Niels N.

    2015-01-01

    A Reynolds-averaged Navier-Stokes code is used to simulate the interaction of two neighboring wind farms. The influence of the Coriolis force is investigated by modeling the atmospheric surface/boundary layer with three different methodologies. The results show that the Coriolis force is negligible...

  2. On atmospheric stability in the dynamic wake meandering model

    DEFF Research Database (Denmark)

    Keck, Rolf-Erik; de Mare, Martin Tobias; Churchfield, Matthew J.

    2014-01-01

    The present study investigates a new approach for capturing the effects of atmospheric stability on wind turbine wake evolution and wake meandering by using the dynamic wake meandering model. The most notable impact of atmospheric stability on the wind is the changes in length and velocity scales...... spectra and applied to the dynamic wake meandering model to capture the correct wake meandering behaviour. The ambient turbulence in all stability classes is generated using the Mann turbulence model, where the effects of non-neutral atmospheric stability are approximated by the selection of input...... in the computational domain. The changes in the turbulent length scales due to the various atmospheric stability states impact the wake meandering characteristics and thus the power generation by the individual turbines. The proposed method is compared with results from both large-eddy simulation coupled...

  3. Wind effect in turbulence parametrization

    Science.gov (United States)

    Colombini, M.; Stocchino, A.

    2005-09-01

    The action of wind blowing over a closed basin ultimately results in a steady shear-induced circulation pattern and in a leeward rising of the free surface—and a corresponding windward lowering—known as wind set-up. If the horizontal dimensions of the basin are large with respect to the average flow depth, the occurrence of local quasi-equilibrium conditions can be expected, i.e. the flow can be assumed to be locally driven only by the wind stress and by the opposing free surface gradient due to set-up. This wind-induced flow configuration shows a strong similarity with turbulent Couette-Poiseuille flow, the one dimensional flow between parallel plates generated by the simultaneous action of a constant pressure gradient and of the shear induced by the relative motion of the plates. A two-equation turbulence closure is then employed to perform a numerical study of turbulent Couette-Poiseuille flows for different values of the ratio of the shear stresses at the two walls. The resulting eddy viscosity vertical distributions are analyzed in order to devise analytical profiles of eddy viscosity that account for the effect of wind. The results of this study, beside allowing for a physical insight on the turbulence process of this class of flows, will allow for a more accurate description of the wind effect to be included in the formulation of quasi-3D and 3D models of lagoon hydrodynamics.

  4. Wind Tunnel Measurements of the Wake of a Full-Scale UH-60A Rotor in Forward Flight

    Science.gov (United States)

    Wadcock, Alan J.; Yamauchi, Gloria K.; Schairer, Edward T.

    2013-01-01

    A full-scale UH-60A rotor was tested in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel in May 2010. The test was designed to acquire a suite of measurements to validate state-of-the-art modeling tools. Measurements include blade airloads (from a single pressure-instrumented blade), blade structural loads (strain gages), rotor performance (rotor balance and torque measurements), blade deformation (stereo-photogrammetry), and rotor wake measurements (Particle Image Velocimetry (PIV) and Retro-reflective Backward Oriented Schlieren (RBOS)). During the test, PIV measurements of flow field velocities were acquired in a stationary cross-flow plane located on the advancing side of the rotor disk at approximately 90 deg rotor azimuth. At each test condition, blade position relative to the measurement plane was varied. The region of interest (ROI) was 4-ft high by 14-ft wide and covered the outer half of the blade radius. Although PIV measurements were acquired in only one plane, much information can be gleaned by studying the rotor wake trajectory in this plane, especially when such measurements are augmented by blade airloads and RBOS data. This paper will provide a comparison between PIV and RBOS measurements of tip vortex position and vortex filament orientation for multiple rotor test conditions. Blade displacement measurements over the complete rotor disk will also be presented documenting blade-to-blade differences in tip-path-plane and providing additional information for correlation with PIV and RBOS measurements of tip vortex location. In addition, PIV measurements of tip vortex core diameter and strength will be presented. Vortex strength will be compared with measurements of maximum bound circulation on the rotor blade determined from pressure distributions obtained from 235 pressure sensors distributed over 9 radial stations.

  5. Wake Conference 2017

    International Nuclear Information System (INIS)

    2017-01-01

    The 52 papers in this volume constitute the proceedings of the 2017 Wake Conference, held in Visby on the island of Gotland, Sweden. The Wake Conference series began in Visby, where it was held in 2009 and 2011. In 2013 the conference took place in Copenhagen where it was combined with the International Conference on Offshore Wind Energy and Ocean Energy. In 2015 it went back to where it started, Visby, and this time it once again takes place at Uppsala University’s Gotland campus, May 30 th - June 1 st . Modern wind turbines are today clustered in large farms with a total production capacity reaching those of a nuclear power plant. When placed in a wind farm, the turbines will be fully or partially influenced by the wake of upstream turbines. This wake interaction results in a decreased power production, caused by the lower kinetic energy in the wind, and an increase in the turbulence intensity. Therefore, understanding the physical nature of vortices and their dynamics in the wake of a turbine is important for the optimal design of wind farms. The increased importance and interest in the field of wake and wind farm aerodynamics can be seen in the increased number of scientific articles on the subject. For example, on the Web of Science citation index, the number citations on the topic ‘wind turbine wakes’ increased from about 50 in 2006 to more than 3800 in 2016. This citation growth essentially shows that the growth in the global production of electrical energy has become a scientific problem to be solved by scientists and engineers. In order to make a substantial impact on one of the most significant challenges of our time, global climate change, the wind industry’s growth must continue. A part of making this growth possible will require research into the physics of wind turbine wakes and wind farms. This conference is aimed at scientists and PhD students working in the field of wake dynamics. The conference covers the following subject areas: Wake and

  6. Effects of Turbine Spacings in Very Large Wind Farms

    DEFF Research Database (Denmark)

    wind farms, although certain aspects of the complex wake interaction are not captured, see Churchfield et al.(2014). Recent studies have shown how turbines introduce low frequencies in the wake, which could describe some of the shortcomings. Chamorro et al.(2015) identified three regions of different...

  7. Linearised CFD models for wakes

    Energy Technology Data Exchange (ETDEWEB)

    Ott, S.; Berg, J.; Nielsen, Morten

    2011-12-15

    This report describes the development of a fast and reasonably accurate model for the prediction of energy production in offshore wind farms taking wake effects into account. The model has been implemented as a windows application called Fuga which can run in batch mode or as a graphical user interface. Fuga is briefly described. The model is based on a linearization technique which is described in some detail, and linearized, governing equations are derived and written in a standard form based on a mixed-spectral formulation. A new solution method is used to solve the equations which involves intensive use of look-up tables for storage of intermediate results. Due to the linearity of the model, multiple wakes from many turbines can be constructed from the wake of a single, solitary turbine. These are in turn constructed from Fourier components by a fast Fourier integral transform of results derived from generic look-up tables. Three different models, based on three different closures, are examined: 1) the 'simple closure' using an unperturbed eddy viscosity kucentre dotz. 2) the mixing length closure. 3) the E-epsilon closure. Model results are evaluated against offshore wind farm production data from Horns Rev I and the Nysted wind farm, and a comparison with direct wake measurements in an onshore turbine (Nibe B) is also made. A very satisfactory agreement with data is found for the simple closure. The exception is the near wake, just behind the rotor, where all three linearized models fail. The mixing length closure underestimates wake effects in all cases. The E-epsilon closure overestimates wake losses in the offshore farms while it predicts a too shallow and too wide the wake in the onshore case. The simple closure performs distinctly better than the other two. Wind speed data from the the Horns rev met masts are used to further validate Fuga results with the 'simple' closure. Finally, Roedsand 1 and 2 are used as an example to illustrate

  8. Characterization of wind velocities in the wake of a full scale wind turbine using three ground-based synchronized WindScanners

    DEFF Research Database (Denmark)

    Yazicioglu, Hasan; Angelou, Nikolas; Mikkelsen, Torben Krogh

    2016-01-01

    , installed at Risoe test field, has been measured from 0 to 2 diameters downstream. For this, three ground-based synchronised short-range WindScanners and a spinner lidar have been used. The 3D wind velocity field has been reconstructed in horizontal and vertical planes crossing the hub. The 10-min mean...

  9. Dynamic wake meandering modeling

    DEFF Research Database (Denmark)

    Larsen, Gunner Chr.; Madsen Aagaard, Helge; Bingöl, Ferhat

    We present a consistent, physically based theory for the wake meandering phenomenon, which we consider of crucial importance for the overall description of wind turbine loadings in wind farms. In its present version the model is confined to single wake situations. The model philosophy does, however......, are an integrated part the model complex. For design applications, the computational efficiency of wake deficit prediction is a key issue. Two computationally low cost models are developed for this purpose. The character of the added wake turbulence, generated by the up-stream turbine in the form of shed......, concerning both flow characteristics and turbine load characteristics. Contrary to previous attempts to model wake loading, the dynamic wake meandering approach opens for a unifying description in the sense that turbine power– and load aspects can be treated simultaneously. This capability is a direct...

  10. Potential Effects of Cannabidiol as a Wake-Promoting Agent

    Science.gov (United States)

    Murillo-Rodríguez, Eric; Sarro-Ramírez, Andrea; Sánchez, Daniel; Mijangos-Moreno, Stephanie; Tejeda-Padrón, Alma; Poot-Aké, Alwin; Guzmán, Khalil; Pacheco-Pantoja, Elda; Arias-Carrión, Oscar

    2014-01-01

    Over the last decades, the scientific interest in chemistry and pharmacology of cannabinoids has increased. Most attention has focused on ∆9-tetrahydrocannabinol (∆9-THC) as it is the psychoactive constituent of Cannabis sativa (C. sativa). However, in previous years, the focus of interest in the second plant constituent with non-psychotropic properties, cannabidiol (CBD) has been enhanced. Recently, several groups have investigated the pharmacological properties of CBD with significant findings; furthermore, this compound has raised promising pharmacological properties as a wake-inducing drug. In the current review, we will provide experimental evidence regarding the potential role of CBD as a wake-inducing drug. PMID:24851090

  11. Using Satellite SAR to Characterize the Wind Flow around Offshore Wind Farms

    Directory of Open Access Journals (Sweden)

    Charlotte Bay Hasager

    2015-06-01

    Full Text Available Offshore wind farm cluster effects between neighboring wind farms increase rapidly with the large-scale deployment of offshore wind turbines. The wind farm wakes observed from Synthetic Aperture Radar (SAR are sometimes visible and atmospheric and wake models are here shown to convincingly reproduce the observed very long wind farm wakes. The present study mainly focuses on wind farm wake climatology based on Envisat ASAR. The available SAR data archive covering the large offshore wind farms at Horns Rev has been used for geo-located wind farm wake studies. However, the results are difficult to interpret due to mainly three issues: the limited number of samples per wind directional sector, the coastal wind speed gradient, and oceanic bathymetry effects in the SAR retrievals. A new methodology is developed and presented. This method overcomes effectively the first issue and in most cases, but not always, the second. In the new method all wind field maps are rotated such that the wind is always coming from the same relative direction. By applying the new method to the SAR wind maps, mesoscale and microscale model wake aggregated wind-fields results are compared. The SAR-based findings strongly support the model results at Horns Rev 1.

  12. Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different turbulent inflow conditions

    Directory of Open Access Journals (Sweden)

    J. Bartl

    2017-02-01

    Full Text Available This is a summary of the results of the fourth blind test workshop that was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at the wind tunnel of the Norwegian University of Science and Technology (NTNU. A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within computational fluid dynamics (CFD were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development with nine rotor diameters downstream at three different turbulent inflow conditions. Aside from a spatially uniform inflow field of very low-turbulence intensity (TI = 0.23 % and high-turbulence intensity (TI = 10.0 %, the turbines are exposed to a grid-generated highly turbulent shear flow (TI = 10.1 %.Five different research groups contributed their predictions using a variety of simulation models, ranging from fully resolved Reynolds-averaged Navier–Stokes (RANS models to large eddy simulations (LESs. For the three inlet conditions, the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. Prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (improved delayed detached eddy simulation model, however

  13. Effect of Wind Direction on ENVISAT ASAR Wind Speed Retrieval

    DEFF Research Database (Denmark)

    Takeyama, Yuko; Ohsawa, Teruo; Kozai, Katsutoshi

    2010-01-01

    This paper presents an evaluation of effects of wind directions (NCEP, MANAL, QuickSCAT and WRF) on the sea surface wind speed retrieval from 75 ENVISAT ASAR images with four C-band Geophysical model functions, CMOD4, CMOD_IFR2, CMOD5 and CMOD5N at two target areas, Hiratsuka and Shirahama...

  14. Analysis of power enhancement for a row of wind turbines using the actuator line technique

    DEFF Research Database (Denmark)

    Mikkelsen, Robert Flemming; Sørensen, Jens Nørkær; Øye, Stig

    2007-01-01

    The effect of wake interaction for a row of three wind turbines in a wind farm is analysed using the actuator line technique. Both full wake and half wake situations are considered with the aim of deriving the optimal pitch setting of the foremost turbine, with respect to the total power from...

  15. PREFACE: Wake Conference 2015

    Science.gov (United States)

    Barney, Andrew; Nørkær Sørensen, Jens; Ivanell, Stefan

    2015-06-01

    The 44 papers in this volume constitute the proceedings of the 2015 Wake Conference, held in Visby on the island of Gotland in Sweden. It is the fourth time this conference has been held. The Wake Conference series started in Visby, where it was held in 2009 and 2011. In 2013 it took place in Copenhagen where it was combined with the International Conference on Offshore Wind Energy and Ocean Energy. In 2015 it is back where it started in Visby, where it takes place at Uppsala University Campus Gotland, June 9th-11th. The global yearly production of electrical energy by wind turbines has grown tremendously in the past decade and it now comprises more than 3% of the global electrical power consumption. Today the wind power industry has a global annual turnover of more than 50 billion USD and an annual average growth rate of more than 20%. State-of-the-art wind turbines have rotor diameters of up to 150 m and 8 MW installed capacity. These turbines are often placed in large wind farms that have a total production capacity corresponding to that of a nuclear power plant. In order to make a substantial impact on one of the most significant challenges of our time, global warming, the industry's growth has to continue for a decade or two yet. This in turn requires research into the physics of wind turbine wakes and wind farms. Modern wind turbines are today clustered in wind farms in which the turbines are fully or partially influenced by the wake of upstream turbines. As a consequence, the wake behind the wind turbines has a lower mean wind speed and an increased turbulence level, as compared to the undisturbed flow outside the farm. Hence, wake interaction results in decreased total production of power, caused by lower kinetic energy in the wind, and an increase in the turbulence intensity. Therefore, understanding the physical nature of the vortices and their dynamics in the wake of a turbine is important for the optimal design of a wind farm. This conference is aimed

  16. Effect of prolonged wakefulness on electroencephalographic oscillatory activity during sleep

    OpenAIRE

    2013-01-01

    The human sleep electroencephalogram (EEG) is characterized by the occurrence of distinct oscillatory events such as delta waves sleep spindles and alpha activity. We applied a previously proposed algorithm for the detection of such events and investigated their incidence and frequency in baseline and recovery sleep after 40 h of sustained wakefulness in 27 healthy young subjects. The changes in oscillatory events induced by sleep deprivation were compared to the corresponding spectral change...

  17. Spectral coherence in windturbine wakes

    Energy Technology Data Exchange (ETDEWEB)

    Hojstrup, J. [Riso National Lab., Roskilde (Denmark)

    1996-12-31

    This paper describes an experiment at a Danish wind farm to investigate the lateral and vertical coherences in the nonequilibrium turbulence of a wind turbine wake. Two meteorological masts were instrumented for measuring profiles of mean speed, turbulence, and temperature. Results are provided graphically for turbulence intensities, velocity spectra, lateral coherence, and vertical coherence. The turbulence was somewhat influenced by the wake, or possibly from aggregated wakes further upstream, even at 14.5 diameters. Lateral coherence (separation 5m) seemed to be unaffected by the wake at 7.5 diameters, but the flow was less coherent in the near wake. The wake appeared to have little influence on vertical coherence (separation 13m). Simple, conventional models for coherence appeared to be adequate descriptions for wake turbulence except for the near wake situation. 3 refs., 7 figs., 1 tab.

  18. Anholt offshore wind farm winds investigated from satellite images

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Badger, Merete; Volker, Patrick

    , i.e. before the wind farm was constructed. Based on these data the wind resource is estimated. Concurrent Sentinel-1 SAR data and available SCADA and lidar data, kindly provided by DONG Energy and partners, for the period January 2013 to June 2015 account for ~70 images, while ~300 images...... are available for Sentinel-1 from July 2015 to February 2017. The Sentinel-1 wind maps are investigated for wind farm wake effects. Furthermore the results on wind resources and wakes are compared to the SCADA and model results from WRF, Park, Fuga and RANS models....

  19. In-operation learning of optimal wind farm operation strategy

    OpenAIRE

    Oliva Gratacós, Joan

    2017-01-01

    In a wind farm, power losses due to wind turbine wake effects can be up to 30-40% under certain conditions. As the global installed wind power capacity increases, the mitigation of wake effects in wind farms is gaining more importance. Following a conventional control strategy, each individual turbine maximizes its own power production without taking into consideration its effects on the performance of downstream turbines. Therefore, this control scheme results in operation con...

  20. Entry of solar-wind ions into the wake of a small body with a magnetic anomaly: A global Vlasov simulation

    Science.gov (United States)

    Umeda, Takayuki; Ito, Yosuke

    2014-04-01

    The interaction between a plasma flow and a small dielectric body with a weak intrinsic global magnetic field is studied by means of a five-dimensional full electromagnetic Vlasov simulation with two configuration spaces and three velocity spaces. In the present study, entry processes of ions into the nightside wake tail are examined. The simulation result shows that the bow shock and the magnetopause are formed on the dayside. However, most of solar-wind ions are reflected at the dayside magnetopause and are picked up by the interplanetary magnetic field. Then, a small part of the reflected ions are taken into the deep wake tail near the body by the E×B cycloid motion.

  1. The effects of sleep, wake activity and time-on-task on offline motor sequence learning.

    Science.gov (United States)

    Landry, Shane; Anderson, Clare; Conduit, Russell

    2016-01-01

    While intervening sleep promotes the consolidation of memory, it is well established that cognitive interference from competing stimuli can impede memory retention. The current study examined changes in motor skill learning across periods of wakefulness with and without competing stimuli, and periods of sleep with and without disruption from external stimuli. A napping study design was adopted where participants (N=44) either had (1) a 30min nap composed of Non-Rapid Eye Movement (NREM) sleep, (2) 30min NREM nap fragmented by audio tone induced arousals, (3) 45min of quiet wakefulness, or (4) 45min of active wakefulness. Measures of subjective sleepiness (KSS), alertness (PVT) and motor skill learning (Sequential Finger Tapping Task, SFTT) were completed in the morning and evening to assess performance pre- and post-nap or wakefulness. Following a practice session, change in motor skill performance was measured over a 10min post training rest interval, as well as following a 7h morning to evening interval comprising one of the four study conditions. A significant offline enhancement in motor task performance (13-23%) was observed following 10min of rest in all conditions. Following the long delay with the intervening nap/wake condition, there were no further offline gains or losses in performance in any sleep (uninterrupted/fragmented) or wake (quiet/active) condition. The current findings suggest that after controlling for offline gains in performance that occur after a brief rest and likely to due to the dissipation of fatigue, the subsequent effect of an intervening sleep or wake period on motor skill consolidation is not significant. Consistent with this null result, the impact of disrupting the sleep episode or manipulating activity during intervening wake also appears to be negligible. Copyright © 2015 Elsevier Inc. All rights reserved.

  2. Effects of dawn simulation on markers of sleep inertia and post-waking performance in humans.

    Science.gov (United States)

    Thompson, Andrew; Jones, Helen; Gregson, Warren; Atkinson, Greg

    2014-05-01

    To examine the effects of a simulated dawn during the last 30 min of sleep on the subsequent dissipation of sleep inertia and changes in simulated work and physical performance. Eight participants, who reported difficulty with morning waking, were administered in a random order to a control (C) and a dawn simulation (DS) trial (starting 30 min prior to waking). Subjective ratings of sleep quality and alertness were obtained alongside measures of cognitive performance (addition and reaction time tasks measured at 5, 30 and 75 min after waking at habitual workday times). Physical performance was also measured 35 min after waking using a self-paced cycling protocol. After waking in DS, perceived sleep quality was 1.16 ± 0.89 (p = 0.01) points higher compared with C. Ratings of alertness were significantly higher in DS than C throughout the testing period (p = 0.04). Cognitive performance improved in both trials as time awake increased (p sleep can increase subjective alertness and improve both cognitive and physical performance after waking.

  3. Effects of superhydrophobic surface on the propeller wake

    Science.gov (United States)

    Choi, Hongseok; Lee, Jungjin; Park, Hyungmin

    2017-11-01

    This study investigates the change in propeller wake when the superhydrophobic surface is applied on the propeller blade. The propeller rotates in a quiescent water tank, facing its bottom, with a rotational Reynolds number of 96000. To measure the three-dimensional flow fields, we use stereo PIV and a water prism is installed at the camera-side tank wall. Two cameras are tilted 30 degrees from the normal axis of the tank wall, satisfying schiempflug condition. Superhydrophobic surface is made by coating hydrophobic nanoparticles on the propeller blade. Measurements are done on two vertical planes (at the center of propeller hub and the blade tip), and are ensemble averaged being classified by blade phase of 0 and 90 degrees. Velocity fluctuation, turbulent kinetic energy, and vorticity are evaluated. With superhydrophobic surface, it is found that the turbulence level is significantly (20 - 30 %) reduced with a small penalty (less than 5%) in the streamwise momentum (i.e., thrust) generation. This is because the cone shaped propeller wake gets narrower and organized vortex structures are broken with the superhydrophobic surfaces. More detailed flow analysis will be given. Supported by NRF (NRF-2016R1C1B2012775, NRF-2016M2B2A9A02945068) programs of Korea government.

  4. A new approach for evaluating measured wake data

    Energy Technology Data Exchange (ETDEWEB)

    Magnusson, Mikael [Uppsala Univ. (Sweden). Dept. of Meteorology

    1996-12-01

    Wind turbine wakes have been studied by analysing a large set of atmospheric data, from a wind farm with four turbines sited on a flat coastal area. The results obtained have ben generalized to allow tests against data from other full scale wind turbines as well as wind tunnel simulations. These comparisons are found to give very satisfactory results. The thrust coefficient is found to be a better parameter for description than wind speed, of wake characteristics because it implicitly includes the effect of regulation. It is also found that down-wind travel time is more convenient to use than down-wind distance in this context. The travel time to the end of the near wake region, i.e. to the point where a single velocity deficit peak first appears, is found to be inversely proportional to the rotational frequency of the turbine and to the turbulence intensity of the ambient air flow and proportional to the ratio of the wake radius and the hub height. For larger travel times, i.e. for the far wake region, it is found that the centre line relative velocity deficit decreases with the logarithm of the time traveled and is parametrically dependent on the time constant and the thrust coefficient. 3 refs, 5 figs

  5. Diversity and noise effects in a model of homeostatic regulation of the sleep-wake cycle.

    Directory of Open Access Journals (Sweden)

    Marco Patriarca

    Full Text Available Recent advances in sleep neurobiology have allowed development of physiologically based mathematical models of sleep regulation that account for the neuronal dynamics responsible for the regulation of sleep-wake cycles and allow detailed examination of the underlying mechanisms. Neuronal systems in general, and those involved in sleep regulation in particular, are noisy and heterogeneous by their nature. It has been shown in various systems that certain levels of noise and diversity can significantly improve signal encoding. However, these phenomena, especially the effects of diversity, are rarely considered in the models of sleep regulation. The present paper is focused on a neuron-based physiologically motivated model of sleep-wake cycles that proposes a novel mechanism of the homeostatic regulation of sleep based on the dynamics of a wake-promoting neuropeptide orexin. Here this model is generalized by the introduction of intrinsic diversity and noise in the orexin-producing neurons, in order to study the effect of their presence on the sleep-wake cycle. A simple quantitative measure of the quality of a sleep-wake cycle is introduced and used to systematically study the generalized model for different levels of noise and diversity. The model is shown to exhibit a clear diversity-induced resonance: that is, the best wake-sleep cycle turns out to correspond to an intermediate level of diversity at the synapses of the orexin-producing neurons. On the other hand, only a mild evidence of stochastic resonance is found, when the level of noise is varied. These results show that disorder, especially in the form of quenched diversity, can be a key-element for an efficient or optimal functioning of the homeostatic regulation of the sleep-wake cycle. Furthermore, this study provides an example of a constructive role of diversity in a neuronal system that can be extended beyond the system studied here.

  6. Group velocity effect on resonant, long-range wake-fields in slow wave structures

    CERN Document Server

    Smirnov, A V

    2002-01-01

    Synchronous wake-fields in a dispersive waveguide are derived in a general explicit form on the basis of a rigorous electro-dynamical approach using Fourier transformations. The fundamental role of group velocity in wake-field propagation, calculation of attenuation, amplitudes, form-factors and loss-factors is analyzed for single bunch radiation. Adiabatic tapering of the waveguide and bunch density variation is taken into account analytically for the time-domain fields. Effects of field 'compression/expansion' and group delays are demonstrated. The role of these effects is discussed for single bunch wake-fields, transient beam loading, BBU and HOMs. A novel waveguide structure with central rf coupling and both positive and negative velocities is proposed. It can be used effectively in both high-energy accelerators and single-section linacs.

  7. A New Approach for Offshore Wind Farm Energy Yields Calculation with Mixed Hub Height Wind Turbines

    DEFF Research Database (Denmark)

    Hou, Peng; Hu, Weihao; Soltani, Mohsen

    2016-01-01

    In this paper, a mathematical model for calculating the energy yields of offshore wind farm with mixed types of wind turbines is proposed. The Jensen model is selected as the base and developed to a three dimension wake model to estimate the energy yields. Since the wind turbines are with differe...... hub heights, the wind shear effect is also taken into consideration. The results show that the proposed wake model is effective in calculating the wind speed deficit. The calculation framework is applicable for energy yields calculation in offshore wind farms.......In this paper, a mathematical model for calculating the energy yields of offshore wind farm with mixed types of wind turbines is proposed. The Jensen model is selected as the base and developed to a three dimension wake model to estimate the energy yields. Since the wind turbines are with different...

  8. Calculation of longitudinal and transverse wake-field effects in dielectric structures

    International Nuclear Information System (INIS)

    Gai, W.

    1989-01-01

    The electro-magnetic radiation of a charged particle passing through a dielectric structure has many applications to accelerator physics. Recently a new acceleration scheme, called the dielectric wake field accelerator, has been proposed. It also can be used as a pick up system for a storage ring because of its slow wave characteristics. In order to study these effects in detail, in this paper we will calculate the wake field effects produced in a dielectric structure by a charged particle. 8 refs., 2 figs

  9. Study on the effects of ion motion on laser-induced plasma wakes

    International Nuclear Information System (INIS)

    Zhou Suyun; Yu Wei; Yuan Xiao; Xu Han; Cao, L. H.; Cai, H. B.; Zhou, C. T.

    2012-01-01

    A 2D analytical model is presented for the generation of plasma wakes (or bubbles) with an ultra-intense laser pulse by taking into account the response of plasma ions. It is shown that the effect of ion motion becomes significant at the laser intensity exceeding 10 21 W/cm 2 and plasma background density below 10 19 cm −3 . In this regime, ion motion tends to suppress the electrostatic field induced by charge separation and makes the electron acceleration less effective. As a result, the assumption of immobile ions overestimates the efficiency of laser wake-field acceleration of electrons. Based on the analytical model, the dynamics of plasma ions in laser-induced wake field is investigated. It is found that only one bubble appears as the plasmas background density exceeds the resonant density and the deposited laser energy is concentrated into the bubble, resulting in the generation of an ion bunch with extremely high energy density.

  10. Effects of sertindole on sleep-wake states, electroencephalogram, behavioral patterns, and epileptic activity of rats

    NARCIS (Netherlands)

    Coenen, A.M.L.; Ates, N.; Skarsfeldt, T.; Luijtelaar, E.L.J.M. van

    1995-01-01

    In this study we addressed the effects of the 5-HT2 receptor antagonist sertindole in rats. The compound was administered in doses of 0.08, 0.32, and 1.28 mg/kg, whereas a control group received the solvent. The effects of sertindole on sleep-wake states, behavioral patterns, and background

  11. Multiple Turbine Wakes

    DEFF Research Database (Denmark)

    Machefaux, Ewan; Mann, Jakob

    and to obtain an estimate of the wake expansion in a fixed frame of reference. A comparison of selected datasets from the campaign showed good far wake agreements of mean wake expansion with Actuator Line CFD computations and simpler engineering models. An empirical relationship, relating maximum wake induction......, the Bulk-Richardson and the Froude number approach. Three test cases are subsequently defined covering various atmospheric conditions. Simulations based on the EllipSys3D ABL flow solver are carried out using Large Eddy Simulation and Actuator disc rotor modeling.The turbulence properties of the incoming...... characteristics was investigated.Later, wake interaction resulting from two stall regulated turbines aligned with the incoming wind were studied experimentally and numerically. The experimental work was based on a new dedicated full-scale measurement campaign involving 3 nacelle mounted Continuous Wave scanning...

  12. CFD three dimensional wake analysis in complex terrain

    Science.gov (United States)

    Castellani, F.; Astolfi, D.; Terzi, L.

    2017-11-01

    Even if wind energy technology is nowadays fully developed, the use of wind energy in very complex terrain is still challenging. In particular, it is challenging to characterize the combination effects of wind ow over complex terrain and wake interactions between nearby turbines and this has a practical relevance too, for the perspective of mitigating anomalous vibrations and loads as well improving the farm efficiency. In this work, a very complex terrain site has been analyzed through a Reynolds-averaged CFD (Computational Fluid Dynamics) numerical wind field model; in the simulation the inuence of wakes has been included through the Actuator Disk (AD) approach. In particular, the upstream turbine of a cluster of 4 wind turbines having 2.3 MW of rated power is studied. The objective of this study is investigating the full three-dimensional wind field and the impact of three-dimensionality on the evolution of the waked area between nearby turbines. A post-processing method of the output of the CFD simulation is developed and this allows to estimate the wake lateral deviation and the wake width. The reliability of the numerical approach is inspired by and crosschecked through the analysis of the operational SCADA (Supervisory Control and Data Acquisition) data of the cluster of interest.

  13. Typhoon Effect on Kuroshio and Green Island Wakes: A Modelling Study

    OpenAIRE

    Tai-Wen Hsu; Meng-Hsien Chou; Wei-Ting Chao; Shin-Jye Liang

    2018-01-01

    Green Island, located in the typhoon-active eastern Taiwan coastal water, is the potential Kuroshio power plant site. In this study, a high resolution (250–2250 m) shallow-water equations model is used to investigate the effect of typhoon on the hydro-dynamics of Kuroshio and Green Island wakes. Two typhoon–Kuroshio interactions—typhoon Soulik and Holland’s typhoon model—are studied. Simulation results of typhoon Soulik indicate salient characteristics of Kuroshio, and downstream island wakes...

  14. Nominal vs. Effective Wake Fields and their Influence on Propeller Cavitation Performance

    DEFF Research Database (Denmark)

    Regener, Pelle Bo; Mirsadraee, Yasaman; Andersen, Poul

    2017-01-01

    Propeller designers often need to base their design on thenominal model scale wake distribution, because the effectivefull scale distribution is not available. The effects of suchincomplete design data on cavitation performance is examinedin this paper. The behind-ship cavitation performanceof two...... flow, with a coupling ofthe two for the interaction of ship and propeller flows. Theeffect on sheet cavitation due to the different wake distributionsis examined for a typical full-form ship. Results showconsiderable differences in cavitation extent, volume, andhull pressure pulses....

  15. Characterizing a Wind Energy Converter's Wake in distinct ABL Conditions by means of Long-Range Lidar Measurements in the Context of the Perdigão 2017 Experiment

    Science.gov (United States)

    Wildmann, N.; Kigle, S.; Hagen, M.; Gerz, T.

    2017-12-01

    As the resource wind is increasingly exploited to produce electricity, wind energy converter (WEC) deployment relocates to more complex terrain such as hilltops or mountain ridges. In that context, it is crucial to understand the interaction between the atmospheric boundary layer (ABL) flow and the WEC in order to predict downstream flow characteristics. In the context of the Perdigão 2017 experiment, the German Aerospace Center (DLR) performed full-scale wake measurements on a single WEC of type Enercon E82 with three Leosphere Windcube 200S long-range scanning lidar systems. The experimental setup covers two parallel ridges 1.4 km apart, separated by a 200 m deep valley. The ridges are oriented in NW-SE direction, perpendicular to main wind direction, which is SW. Two of the three scanning lidar systems are positioned downstream of the WEC in line with main wind direction to span a vertical plane, perpendicular to the ridges, with RHI scans. This allows investigating wake events with single or dual-doppler lidar techniques. The third lidar system, which is positioned along the WEC ridge, is used to measure the wake position outside the before mentioned measurement plane. Wake events in three different ABL regimes (neutral, stable and convective) are evaluated with respect to wake position, dispersion, propagation and the wind-speed deficit. It is found that wake position and propagation are strongly influenced by the atmospheric stability, forcing the wake to deviate from hub height, migrating to higher levels for convective regimes. For stable ABL conditions wakes descend into the valley, and are clearly detectable up to at least eight rotor diameters downstream of the WEC. The coplanar scanning strategy furthermore allows to calculate the two-dimensional wind vector in the vertical scanning plane, indicating that vertical wind components with up to 2 ms-1 play an important role in the interaction between ABL flow and WEC. With the help of the third lidar

  16. Effects of aging and housing in an enriched environment on sleep-wake patterns in rats

    NARCIS (Netherlands)

    van Gool, W. A.; Mirmiran, M.

    1986-01-01

    The effects of aging and housing in an enriched environment were assessed in young adult (4-7 months) and old (27-31 months) male Brown Norway rats by conducting 24-h sleep-wake recordings. Comparison of recordings made in rats of different ages, housed in a standard laboratory environment, revealed

  17. Reliability Analysis of Wind Turbines

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Sørensen, John Dalsgaard

    2008-01-01

    In order to minimise the total expected life-cycle costs of a wind turbine it is important to estimate the reliability level for all components in the wind turbine. This paper deals with reliability analysis for the tower and blades of onshore wind turbines placed in a wind farm. The limit states......) the reliability level for a wind turbine placed in a wind farm is considered, and wake effects from neighbouring wind turbines is taken into account. An illustrative example with calculation of the reliability for mudline bending of the tower is considered. In the example the design is determined according...

  18. Effectiveness of Changing Wind Turbine Cut-in Speed to Reduce Bat Fatalities at Wind Facilities

    Energy Technology Data Exchange (ETDEWEB)

    Huso, Manuela M. P. [Oregon State Univ., Corvallis, OR (United States); Hayes, John P. [Univ. of Florida, Gainesville, FL (United States)

    2009-04-01

    This report details an experiment on the effectiveness of changing wind turbine cut-in speed on reducing bat fatality from wind turbines at the Casselman Wind Project in Somerset County, Pennsylvania.

  19. Disharmony between wake- and respiration-promoting activities: effects of modafinil on ventilatory control in rodents.

    Science.gov (United States)

    Terada, Jiro; Fukushi, Isato; Takeda, Kotaro; Hasebe, Yohei; Pokorski, Mieczyslaw; Tatsumi, Koichiro; Okada, Yasumasa

    2016-11-14

    Modafinil is a wake-promoting drug and has been widely used for daytime sleepiness in patients with narcolepsy and other sleep disorders. A recent case series reported that daily oral modafinil alleviated hypercapnic respiratory failure in patients with COPD. However, the precise action of modafinil on respiration such as hypercapnic and/or hypoxic ventilatory responses remains unclear. The aim of this study is to clarify the effect of modafinil on the ventilatory control. We investigated the hypothesis that modafinil enhances resting ventilation as well as the stimulatory ventilatory responses to hypercapnia and hypoxia. We addressed the issue by examining minute ventilation, respiratory rate and volume components using plethysmography, combined with a concurrent EEG monitoring of the level of wakefulness before and after administration of modafinil in two doses of 100 mg/kg and 200 mg/kg in unanesthetized mice. In addition, we monitored the effect of the lower dose of modafinil on mice locomotor activity in a freely moving condition by video-recording. Wakefulness, locomotor activity and variability of the breathing pattern in tidal volume were promoted by both doses of modafinil. Neither dose of modafinil increased the absolute values of resting ventilation or promoted the ventilatory responses to hypercapnia and hypoxia. Rather, higher dose of modafinil slightly suppressed respiratory rate in room air condition. Modafinil is conducive to the state of wakefulness but does not augment resting ventilation or the hyperventilatory responses to chemical stimuli in unanesthetized rodents.

  20. Empirical investigation of wind farm blockage effects in Horn Rev 1 offshore wind farm

    DEFF Research Database (Denmark)

    Mitraszewski, Karol; Hansen, Kurt Schaldemose; Nygaard, Nicolai

    We present an empirical study of wind farm blockage effects based on Horns Rev 1 SCADA data. The mean inflow non-uniformities in wind speed are analyzed by calculating the mean power outputs of turbines located along the outer edges of the farm for different wind directions, wind speeds and stabi......We present an empirical study of wind farm blockage effects based on Horns Rev 1 SCADA data. The mean inflow non-uniformities in wind speed are analyzed by calculating the mean power outputs of turbines located along the outer edges of the farm for different wind directions, wind speeds...

  1. A consistent turbulence formulation for the dynamic wake meandering model in the atmospheric boundary layer

    DEFF Research Database (Denmark)

    Keck, Rolf-Erik; Veldkamp, Dick; Wedel-Heinen, Jens Jakob

    as a standalone flow-solver for the velocity and turbulence distribution, and power production in a wind farm. The performance of the standalone implementation is validated against field data, higher-order computational fluid dynamics models, as well as the most common engineering wake models in the wind industry...... evolution 4. atmospheric stability effects on wake deficit evolution and meandering The conducted research is to a large extent based on detailed wake investigations and reference data generated through computational fluid dynamics simulations, where the wind turbine rotor has been represented......This thesis describes the further development and validation of the dynamic meandering wake model for simulating the flow field and power production of wind farms operating in the atmospheric boundary layer (ABL). The overall objective of the conducted research is to improve the modelling...

  2. The impact of turbulence intensity and atmospheric stability on power deficits due to wind turbine wakes at Horns Rev wind farm

    DEFF Research Database (Denmark)

    Hansen, Kurt Schaldemose; Barthelmie, Rebecca J.; Jensen, Leo E.

    2012-01-01

    unstable conditions, whereas northerly winds have fewer observations in the stable classes. Stable conditions also tend to be associated with lower levels of turbulence intensity, and this relationship persists as wind speeds increase. Power deficit is a function of ambient turbulence intensity. The level...

  3. Cross-winds effect on the performance of natural draft wet cooling towers

    Energy Technology Data Exchange (ETDEWEB)

    Al-Waked, R. [Dhofar Univ., Mechanical Engineering Dept., College of Engineering, Sultanate of Oman (Oman)

    2010-01-15

    Effects of cross-winds on the thermal performance of natural draft wet cooling towers (NDWCTs) have been investigated. A three-dimensional CFD model has been used to determine the effect of cross-winds on NDWCTs performance surrounded by power plant building structures. The three-dimensional CFD model has utilized the standard k-{epsilon} turbulence model as the turbulence closure. Two cases have been investigated: a stand-alone NDWCT and two NDWCTs within a proposed power plant structures (PPS). It has been found that regardless of the cross-winds direction, an increase of 1.3 k or more could be predicted at cross-winds speeds greater than 4 m/s. Furthermore, the performance of NDWCTs under cross-winds has been found to be dependent on the three major factors: the structure of the approaching cross-winds and whether it is disturbed or undisturbed, the location of the NDWCT in the wake of the other NDWCT, and the location of the NDWCT in front of/in the wake of the PPS. When comparing results from the stand-alone and from the NDWCTs within PPS simulations, differences in {delta}T{sub wo} were found to be less than 1 K for the whole span of cross-winds speeds and could be decreased to 0.7 K for speeds less than 8 m/s. Finally, results obtained from the simulation of a stand-alone NDWCT could be used instead of those from NDWCTs within PPS at a certain cross-winds direction for qualitative comparisons. (authors)

  4. Cross-winds effect on the performance of natural draft wet cooling towers

    International Nuclear Information System (INIS)

    Al-Waked, R.

    2010-01-01

    Effects of cross-winds on the thermal performance of natural draft wet cooling towers (NDWCTs) have been investigated. A three-dimensional CFD model has been used to determine the effect of cross-winds on NDWCTs performance surrounded by power plant building structures. The three-dimensional CFD model has utilized the standard k-ε turbulence model as the turbulence closure. Two cases have been investigated: a stand-alone NDWCT and two NDWCTs within a proposed power plant structures (PPS). It has been found that regardless of the cross-winds direction, an increase of 1.3 k or more could be predicted at cross-winds speeds greater than 4 m/s. Furthermore, the performance of NDWCTs under cross-winds has been found to be dependent on the three major factors: the structure of the approaching cross-winds and whether it is disturbed or undisturbed, the location of the NDWCT in the wake of the other NDWCT, and the location of the NDWCT in front of/in the wake of the PPS. When comparing results from the stand-alone and from the NDWCTs within PPS simulations, differences in ΔT wo were found to be less than 1 K for the whole span of cross-winds speeds and could be decreased to 0.7 K for speeds less than 8 m/s. Finally, results obtained from the simulation of a stand-alone NDWCT could be used instead of those from NDWCTs within PPS at a certain cross-winds direction for qualitative comparisons. (authors)

  5. Effects of modafinil and amphetamine on sleep-wake cycle after sleep deprivation in cats.

    Science.gov (United States)

    Hou, Y P; Lin, J S

    1999-09-01

    The effects of modafinil and amphetamine on sleep-wake cycle and cortical power spectrum were assessed in the cats before and after sleep deprivation. The sleep deprivation in the cats was used with the water tank technique. Cats were administrated with modafinil (5 mg.kg-1 p.o.) or amphetamine (1 mg.kg-1) before and after sleep deprivation. The waking effect of 8-10 h induced by modafinil before and after sleep deprivation was similar and was not followed by an increase in sleep rebound. On the contrary, the arousal effect about 8 h evoked by amphetamine after sleep deprivation was less lasting than that of 10-12 h observed in normal conditions and followed by an amplified rebound in both deep slow wave sleep and paradoxical sleep. These results suggest the efficiency of modafinil against somnolence and hypersomnia without increasing subsequent sleep.

  6. Wind energy applications of synthetic aperture radar

    Energy Technology Data Exchange (ETDEWEB)

    Bruun Christiansen, M.

    2006-11-15

    Synthetic aperture radars (SAR), mounted on satellites or aircraft, have proven useful for ocean wind mapping. Wind speeds at the height 10 m may be retrieved from measurements of radar backscatter using empirical model functions. The resulting wind fields are valuable in offshore wind energy planning as a supplement to on site measurements, which are costly and sparse, and model wind fields, which are not fully validated. Two applications of SAR measurements in offshore wind energy planning are addressed here: the study of wind farm wake effects and the potential of using SAR winds in offshore wind resource assessment. Firstly, wind wakes behind two large offshore wind farms in Denmark Horns Rev and Nysted are identified. A region of reduced wind speed is found downstream of both wind farms from the SAR wind fields. The wake extent and magnitude depends on the wind speed, the atmospheric stability, and the fraction of turbines operating. Wind farm wake effects are detected up to 20 km downwind of the last turbine. This distance is longer than predicted by state-of-the art wake models. Wake losses are typically 10-20% near the wind farms. Secondly, the potential of using SAR wind maps in offshore wind resource assessment is investigated. The resource assessment is made through Weibull fitting to frequency observations of wind speed and requires at least 100 satellite observations per year for a given site of interest. Predictions of the energy density are very sensitive to the wind speed and the highest possible accuracy on SAR wind retrievals is therefore sought. A 1.1 m s{sup -1} deviation on the mean wind speed is found through comparison with mast measurements at Horns Rev. The accuracy on mean wind speeds and energy densities found from satellite measurements varies with different empirical model functions. Additional uncertainties are introduced by the infrequent satellite sampling at fixed times of the day. The accuracy on satellite based wind resource

  7. Analysis of a high brightness photo electron beam with self field and wake field effects

    International Nuclear Information System (INIS)

    Parsa, Z.

    1991-01-01

    High brightness sources are the basic ingredients in the new accelerator developments such as Free-Electron Laser experiments. The effects of the interactions between the highly charged particles and the fields in the accelerating structure, e.g. R.F., Space charge and Wake fields can be detrimental to the beam and the experiments. We present and discuss the formulation used, some simulation and results for the Brookhaven National Laboratory high brightness beam that illustrates effects of the accelerating field, space charge forces (e.g. due to self field of the bunch), and the wake field (e.g. arising from the interaction of the cavity surface and the self field of the bunch)

  8. Disharmony between wake- and respiration-promoting activities: effects of modafinil on ventilatory control in rodents

    OpenAIRE

    Terada, Jiro; Fukushi, Isato; Takeda, Kotaro; Hasebe, Yohei; Pokorski, Mieczyslaw; Tatsumi, Koichiro; Okada, Yasumasa

    2016-01-01

    Background Modafinil is a wake-promoting drug and has been widely used for daytime sleepiness in patients with narcolepsy and other sleep disorders. A recent case series reported that daily oral modafinil alleviated hypercapnic respiratory failure in patients with COPD. However, the precise action of modafinil on respiration such as hypercapnic and/or hypoxic ventilatory responses remains unclear. The aim of this study is to clarify the effect of modafinil on the ventilatory control. Methods ...

  9. Heat transfer behavior including thermal wake effects in forced air cooling of arrays of rectangular blocks

    International Nuclear Information System (INIS)

    Sridhar, S.; Faghri, M.; Lessmann, R.C.

    1990-01-01

    Experiments have been carried out to study thermal wake effects in arrays of rectangular blocks encountered in electronic equipment. Data were obtained for a series of channel heights and flow velocities. The temperature rise due to wake effects behind a single heated module was found to be fairly independent of the channel height and the position of the heated block, for a given approach velocity. The adiabatic temperature rise data for a module due to a heated element immediately upstream of it for different inter-module spacings were found to correlate well in terms of a new parameter called the surface packing density. This paper reports that it was reported by the authors in an earlier paper that both the adiabatic heat transfer coefficient nd pressure-drop data for regular in-line arrays correlated well in terms of a composite geometric parameter called the column packing density. These experiments have been extended to a higher Reynolds number. Empirical correlations are presented here for friction factor and Nusselt number in terms of the volume packing density, and for the thermal wake effects in terms of the surface packing density. Data from literature for arrays with widely different geometric parameters are shown to agree with these correlations

  10. The effects of a nighttime nap on the error-monitoring functions during extended wakefulness.

    Science.gov (United States)

    Asaoka, Shoichi; Fukuda, Kazuhiko; Murphy, Timothy I; Abe, Takashi; Inoue, Yuichi

    2012-06-01

    To examine the effects of a 1-hr nighttime nap, and the associated sleep inertia, on the error-monitoring functions during extended wakefulness using the 2 event-related potential components thought to reflect error detection and emotional or motivational evaluation of the error, i.e., the error-related negativity/error-negativity (ERN/Ne) and error-positivity (Pe), respectively. Participants awakened at 07:00 the morning of the experimental day, and performed a stimulus-response compatibility (arrow-orientation) task at 21:00, 02:00, and 03:00. A cognitive task with EEG data recording was performed in a laboratory setting. Twenty young adults (mean age 21.3 ± 1.0 yr, 14 males) participated. Half of the participants took a 1-hr nap, and the others had a 1-hr awake-rest period from 01:00-02:00. Behavioral performance and amplitude of the Pe declined after midnight (i.e., 02:00 and 03:00) compared with the 21:00 task period in both groups. During the task period starting at 03:00, the participants in the awake-rest condition reported less alertness and showed fewer correct responses than those who napped. However, there were no effects of a nap on the amplitude of the ERN/Ne or Pe. Our results suggest that a 1-hr nap can alleviate the decline in subjective alertness and response accuracy during nighttime; however, error-monitoring functions, especially emotional or motivational evaluation of the error, might remain impaired by extended wakefulness even after the nap. This phenomenon could imply that night-shift workers experiencing extended wakefulness should not overestimate the positive effects of a nighttime 1-hr nap during extended wakefulness.

  11. Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine.

    Science.gov (United States)

    Hong, Jiarong; Toloui, Mostafa; Chamorro, Leonardo P; Guala, Michele; Howard, Kevin; Riley, Sean; Tucker, James; Sotiropoulos, Fotis

    2014-06-24

    To improve power production and structural reliability of wind turbines, there is a pressing need to understand how turbines interact with the atmospheric boundary layer. However, experimental techniques capable of quantifying or even qualitatively visualizing the large-scale turbulent flow structures around full-scale turbines do not exist today. Here we use snowflakes from a winter snowstorm as flow tracers to obtain velocity fields downwind of a 2.5-MW wind turbine in a sampling area of ~36 × 36 m(2). The spatial and temporal resolutions of the measurements are sufficiently high to quantify the evolution of blade-generated coherent motions, such as the tip and trailing sheet vortices, identify their instability mechanisms and correlate them with turbine operation, control and performance. Our experiment provides an unprecedented in situ characterization of flow structures around utility-scale turbines, and yields significant insights into the Reynolds number similarity issues presented in wind energy applications.

  12. Effects of Low Reynolds Number on Wake-Generated Unsteady Flow of an Axial-Flow Turbine Rotor

    Directory of Open Access Journals (Sweden)

    Matsunuma Takayuki

    2005-01-01

    Full Text Available The unsteady flow field downstream of axial-flow turbine rotors at low Reynolds numbers was investigated experimentally using hot-wire probes. Reynolds number, based on rotor exit velocity and rotor chord length Re out,RT , was varied from 3.2× 10 4 to 12.8× 10 4 at intervals of 1.0× 10 4 by changing the flow velocity of the wind tunnel. The time-averaged and time-dependent distributions of velocity and turbulence intensity were analyzed to determine the effect of Reynolds number. The reduction of Reynolds number had a marked influence on the turbine flow field. The regions of high turbulence intensity due to the wake and the secondary vortices were increased dramatically with the decreasing Reynolds number. The periodic fluctuation of the flow due to rotor-stator interaction also increased with the decreasing Reynolds number. The energy-dissipation thickness of the rotor midspan wake at the low Reynolds number Re out,RT =3.2× 10 4 was 1.5 times larger than that at the high Reynolds number Re out,RT =12.8× 10 4 . The curve of the −0.2 power of the Reynolds number agreed with the measured energy-dissipation thickness at higher Reynolds numbers. However, the curve of the −0.4 power law fitted more closely than the curve of the −0.2 power law at lower Reynolds numbers below 6.4× 10 4 .

  13. Effects of Methamphetamine on Vigilance and Tracking during Extended Wakefulness.

    Science.gov (United States)

    1993-09-01

    Effects of modafinil on the nocturnal activity and behavioural sleep of rhesus monkeys (Maccaca mulatta). Medical Science Research, 18, 397-399...vigilance and tracking performance in a 13.5-h sustained-performance session during a night of sleep loss. At 0116 hours, seven subjects were... sleep loss. DTIO QUAI.TY INSPECTE-tD 5 .I IC I Of ...................................................... i .’I ; )I ACKNOWLEDGEMENTS In particular, we

  14. Quantifying offshore wind resources from satellite wind maps: Study area the North Sea

    DEFF Research Database (Denmark)

    Hasager, Charlotte Bay; Barthelmie, Rebecca Jane; Christiansen, Merete B.

    2006-01-01

    Offshore wind resources are quantified from satellite synthetic aperture radar (SAR) and satellite scatterometer observations at local and regional scale respectively at the Horns Rev site in Denmark. The method for wind resource estimation from satellite observations interfaces with the wind atlas...... of the Horns Rev wind farm is quantified from satellite SAR images and compared with state-of-the-art wake model results with good agreement. It is a unique method using satellite observations to quantify the spatial extent of the wake behind large offshore wind farms. Copyright © 2006 John Wiley & Sons, Ltd....... analysis and application program (WAsP). An estimate of the wind resource at the new project site at Horns Rev is given based on satellite SAR observations. The comparison of offshore satellite scatterometer winds, global model data and in situ data shows good agreement. Furthermore, the wake effect...

  15. Longitudinal effects of near-uniform beam-wall wake fields

    International Nuclear Information System (INIS)

    Ruggiero, A.G.; Talmann, R.

    1979-01-01

    Several theories have been developed in the past to explain longitudinal instabilities of individual bunches in particle accelerators and storage rings. But they are less than satisfactory because in one way or another they rely on some mathematical approximation of doubtful physical meaning. Here, the basic physical model is simplified in order to help to understand a little better the physics involved. Initially, the motion of two particles executing phase oscillations in the same bunch under the influence of the wake field generated by the other is investigated. This motion is stable and bounded even for the case of a slowly varying wake field. But the distortions of the trajectories can, nevertheless, be significant and can be interpreted as bunch lengthening and widening. These models generalized to an N particle model. If the wake field is constant, the equations are simple enough that it is possible to solve exactly for the intensity-limited, self-consistent, longitudinal particle distribution. It is not necessary to solve, or even introduce, the Vlasov equation. These models exhibit effects like dipole and quadrupole oscillations and bunch lengthening, in qualitative agreement with observed behavior, but no attempt has been made at quantitative comparison with observation

  16. Industrial wind turbines and adverse health effects.

    Science.gov (United States)

    Jeffery, Roy D; Krogh, Carmen M E; Horner, Brett

    2014-01-01

    Some people living in the environs of industrial wind turbines (IWTs) report experiencing adverse health and socioeconomic effects. This review considers the hypothesis that annoyance from audible IWTs is the cause of these adverse health effects. We searched PubMed and Google Scholar for articles published since 2000 that included the terms "wind turbine health," "wind turbine infrasound," "wind turbine annoyance," "noise annoyance" or "low frequency noise" in the title or abstract. Industrial wind turbines produce sound that is perceived to be more annoying than other sources of sound. Reported effects from exposure to IWTs are consistent with well-known stress effects from persistent unwanted sound. If placed too close to residents, IWTs can negatively affect the physical, mental and social well-being of people. There is sufficient evidence to support the conclusion that noise from audible IWTs is a potential cause of health effects. Inaudible low-frequency noise and infrasound from IWTs cannot be ruled out as plausible causes of health effects.

  17. Offshore Wind Farm Layout Design Considering Optimized Power Dispatch Strategy

    DEFF Research Database (Denmark)

    Hou, Peng; Hu, Weihao; N. Soltani, Mohsen

    2017-01-01

    Offshore wind farm has drawn more and more attention recently due to its higher energy capacity and more freedom to occupy area. However, the investment is higher. In order to make a cost-effective wind farm, the wind farm layout should be optimized. The wake effect is one of the dominant factors...

  18. Validation of the standalone implementation of the dynamic wake meandering model for power production

    DEFF Research Database (Denmark)

    Keck, Rolf-Erik Henrik Jussi

    2015-01-01

    This paper presents validation for using the standalone implementation of the dynamic wake meandering (DWM) model to conduct numerical simulations of power production of rows of wind turbines. The standalone DWM model is an alternative formulation of the conventional DWM model that does not require...... be seen as an alternative for simulating the power production of a wind farm. The main advantage of the standalone DWM model is the ability to capture the key physics for wake dynamics such as the turbine specific induction, the build‐up of wake turbulence and wake deficit in the wind farm, and the effect...... information exchange with an aeroelastic code. As a consequence, the standalone DWM model has significantly shorter computational times and lower demands on the user environment. The drawback of the standalone DWM model is that it does not have the capability to predict turbine loads. Instead, it should...

  19. Structural Reliability Aspects in Design of Wind Turbines

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard

    2007-01-01

    Reliability assessment, optimal design and optimal operation and maintenance of wind turbines are an area of significant interest for the fast growing wind turbine industry for sustainable production of energy. Offshore wind turbines in wind farms give special problems due to wake effects inside...... the farm. Reliability analysis and optimization of wind turbines require that the special conditions for wind turbine operation are taken into account. Control of the blades implies load reductions for large wind speeds and parking for high wind speeds. In this paper basic structural failure modes for wind...

  20. Effects of Yaw Error on Wind Turbine Running Characteristics Based on the Equivalent Wind Speed Model

    Directory of Open Access Journals (Sweden)

    Shuting Wan

    2015-06-01

    Full Text Available Natural wind is stochastic, being characterized by its speed and direction which change randomly and frequently. Because of the certain lag in control systems and the yaw body itself, wind turbines cannot be accurately aligned toward the wind direction when the wind speed and wind direction change frequently. Thus, wind turbines often suffer from a series of engineering issues during operation, including frequent yaw, vibration overruns and downtime. This paper aims to study the effects of yaw error on wind turbine running characteristics at different wind speeds and control stages by establishing a wind turbine model, yaw error model and the equivalent wind speed model that includes the wind shear and tower shadow effects. Formulas for the relevant effect coefficients Tc, Sc and Pc were derived. The simulation results indicate that the effects of the aerodynamic torque, rotor speed and power output due to yaw error at different running stages are different and that the effect rules for each coefficient are not identical when the yaw error varies. These results may provide theoretical support for optimizing the yaw control strategies for each stage to increase the running stability of wind turbines and the utilization rate of wind energy.

  1. Numerical Study of a Long-Lived, Isolated Wake Vortex in Ground Effect

    Science.gov (United States)

    Proctor, Fred H.

    2014-01-01

    This paper examines a case observed during the 1990 Idaho Falls Test program, in which a wake vortex having an unusually long lifetime was observed while in ground effect. A numerical simulation is performed with a Large Eddy Simulation model to understand the response of the environment in affecting this event. In the simulation, it was found that one of the vortices decayed quickly, with the remaining vortex persisting beyond the time-bound of typical vortex lifetimes. This unusual behavior was found to be related to the first and second vertical derivatives of the ambient crosswind.

  2. Wake modelling combining mesoscale and microscale models

    DEFF Research Database (Denmark)

    Badger, Jake; Volker, Patrick; Prospathospoulos, J.

    2013-01-01

    parameterizations are demonstrated in theWeather Research and Forecasting mesoscale model (WRF) in an idealized atmospheric flow. The model framework is the Horns Rev I wind farm experiencing an 7.97 m/s wind from 269.4o. Three of the four parameterizations use thrust output from the CRESflow-NS microscale model......In this paper the basis for introducing thrust information from microscale wake models into mesocale model wake parameterizations will be described. A classification system for the different types of mesoscale wake parameterizations is suggested and outlined. Four different mesoscale wake....... The characteristics of the mesoscale wake that developed from the four parameterizations are examined. In addition the mesoscale model wakes are compared to measurement data from Horns Rev I. Overall it is seen as an advantage to incorporate microscale model data in mesocale model wake parameterizations....

  3. Bifurcation of space-charge wave in a plasma waveguide including the wake potential effect

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Myoung-Jae [Department of Physics and Research Institute for Natural Sciences, Hanyang University, Seoul 04763 (Korea, Republic of); Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr [Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 15588, South Korea and Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States)

    2016-09-15

    The wake potential effects on the propagation of the space-charge dust ion-acoustic wave are investigated in a cylindrically bounded dusty plasma with the ion flow. The results show that the wake potential would generate the double frequency modes in a cylindrically bounded dusty plasma. It is found that the upper mode of the wave frequency with the root of higher-order is smaller than that with the root of lower-order in intermediate wave number domains. However, the lower mode of the scaled wave frequency with the root of higher-order is found to be greater than that with the root of lower-order. It is found that the influence in the order of the root of the Bessel function on the wave frequency of the space-charge dust-ion-acoustic wave in a cylindrically confined dusty plasma decreases with an increase in the propagation wave number. It is also found that the double frequency modes increase with increasing Mach number due to the ion flow in a cylindrical dusty plasma. In addition, it is found that the upper mode of the group velocity decreases with an increase in the scaled radius of the plasma cylinder. However, it is shown that the lower mode of the scaled group velocity of the space-charge dust ion acoustic wave increases with an increase in the radius of the plasma cylinder. The variation of the space-charge dust-ion-acoustic wave due to the wake potential and geometric effects is also discussed.

  4. A wind-tunnel investigation of parameters affecting helicopter directional control at low speeds in ground effect

    Science.gov (United States)

    Yeager, W. T., Jr.; Young, W. H., Jr.; Mantay, W. R.

    1974-01-01

    An investigation was conducted in the Langley full-scale tunnel to measure the performance of several helicopter tail-rotor/fin configurations with regard to directional control problems encountered at low speeds in ground effect. Tests were conducted at wind azimuths of 0 deg to 360 deg in increments of 30 deg and 60 deg and at wind speeds from 0 to 35 knots. The results indicate that at certain combinations of wind speed and wind azimuth, large increases in adverse fin force require correspondingly large increases in the tail-rotor thrust, collective pitch, and power required to maintain yaw trim. Changing the tail-rotor direction of rotation to top blade aft for either a pusher tail rotor (tail-rotor wake blowing away from fin) or a tractor tail rotor (tail-rotor wake blowing against fin) will alleviate this problem. For a pusher tail rotor at 180 deg wind azimuth, increases in the fin/tail-rotor gap were not found to have any significant influence on the overall vehicle directional control capability. Changing the tail rotor to a higher position was found to improve tail-rotor performance for a fin-off configuration at a wind azimuth of 180 deg. A V-tail configuration with a pusher tail rotor with top blade aft direction of rotation was found to be the best configuration with regard to overall directional control capability.

  5. Reynolds number effect on airfoil wake structures under pitching and heaving motion

    Science.gov (United States)

    Kim, Kyung Chun; Karbasian, Hamidreza; ExpTENsys Team

    2017-11-01

    Detached Eddy Simulation (DES) and particle image velocimetry (PIV) measurements were performed to investigate the wake flow characteristics of an airfoil under pitching and heaving motion. A NACA0012 airfoil was selected for the numerical simulation and experiments were carried out in a wind tunnel and a water tunnel at Reynolds number of 15,000 and 90,000, respectively. The airfoil oscillated around an axis located 1/4 distance from the leading edge chord. Two different angles of attack, 20° and 30°, were selected with +/-10° maximum amplitude of oscillation. In order to extract the coherent flow structures from time-resolved PIV data, proper orthogonal decomposition (POD) analysis was performed on 1,000 instantaneous realisations for each condition using the method of snapshots. Vorticity contour and velocity profiles for both PIV and DES results are in good agreement for pitching and heaving motion. At high Reynolds number, 3D stream-wise vortices appeared after generating span-wise vortices. The higher maximum angle of attack allows the leading edge vortex to grow stronger and that the angle of attack appears to be more important in influencing the growth of the leading edge vortex structure than the reduced frequency. National Research Foundation of Korea (No. 2011-0030013).

  6. Estimating the true energy value of a wind farm

    International Nuclear Information System (INIS)

    Bass, J.

    1995-01-01

    To assess the true energy yield of a wind farm taking into account real-world effects such as control losses in individual turbines, losses in the distribution network and wake and topographic effects, this report from the Energy Technology Support Unit, has developed a more appropriate methodology for making economic assessments of wind farm projects. Simulations of wind turbines are used to enable control losses to be quantified, and long term performance data from wind turbines in operational United Kingdom wind farms adds to the accuracy of assessment. A model has also been used to estimate performance of a power distribution system for a wind farm, to enable losses associated with wind turbine, wind speed and various distribution layouts to be predicted. Data on wake effects are drawn from a separate study. All these are drawn into an economic simulation model which predicts a wind farm's likely achievement of its target energy yield, thus demonstrating the risk factors involved. (UK)

  7. Self-reported effects of dreams on waking-life creativity: an empirical study.

    Science.gov (United States)

    Schredl, Michael; Erlacher, Daniel

    2007-01-01

    The authors studied the self-rated effect of dreams on creativity in participants who were not selected for creative abilities. Students (N = 444) and online respondents (N = 636) answered a questionnaire about dreams and creative dreams. In addition, the students completed several personality measures and creativity scales. Results indicated that dreams that stimulated waking-life creativity played a considerable role in the lives of ordinary people (about 8% of all dreams). Examples reported by the online participants fell into 4 categories: (a) dream images used for art, work, or similar areas; (b) dreams that solved a problem; (c) dreams that provided the impetus to do something that the dreamer otherwise had difficulty doing; and (d) dreams containing emotional insights. The main factors influencing frequency of creative dreams were dream recall frequency and the thin boundaries personality dimension. Future researchers should use diary techniques to study the effects of dreams on waking life and should develop techniques to increase the frequency of creative dreams that might be valuable as aids for people in creative jobs.

  8. Denmark Wind Energy Programme

    DEFF Research Database (Denmark)

    Shen, Wen Zhong

    2014-01-01

    In this paper, a summary of some ongoing wind energy projects in Denmark is given. The research topics comprise computational model development, wind turbine design, low noise airfoil and blade design, control device development, wake modelling, and wind farm layout optimization.......In this paper, a summary of some ongoing wind energy projects in Denmark is given. The research topics comprise computational model development, wind turbine design, low noise airfoil and blade design, control device development, wake modelling, and wind farm layout optimization....

  9. Numerical study on wake characteristics of high-speed trains

    Science.gov (United States)

    Yao, Shuan-Bao; Sun, Zhen-Xu; Guo, Di-Long; Chen, Da-Wei; Yang, Guo-Wei

    2013-12-01

    Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.

  10. Considering induction factor using BEM method in wind farm layout optimization

    DEFF Research Database (Denmark)

    Ghadirian, Amin; Dehghan, M.; Torabi, F.

    2014-01-01

    For wind farm layout optimization process, a simple linear model has been mostly used for considering the wake effect of a wind turbine on its downstream turbines. In this model, the wind velocity in the wake behind a turbine is obtained as a function of turbine induction factor which was conside......For wind farm layout optimization process, a simple linear model has been mostly used for considering the wake effect of a wind turbine on its downstream turbines. In this model, the wind velocity in the wake behind a turbine is obtained as a function of turbine induction factor which...... and consequently influences the farm layout in optimization process. (C) 2014 Elsevier Ltd. All rights reserved....

  11. Dynamic screening and wake effects on electronic excitation in ion-solid and ion-surface collisions

    Energy Technology Data Exchange (ETDEWEB)

    Burgdoerfer, J. (Tennessee Univ., Knoxville, TN (United States). Dept. of Physics Oak Ridge National Lab., TN (United States))

    1991-01-01

    The collective electronic response in a solid effectively alters ionic and atomic potentials giving rise to dynamic screening and to a wake'' of density fluctuations trailing ions as they propagate through the solid. The presence of dynamic screening modifies electronic excitation processes of projectiles in ion-solid collisions as compared to binary ion-atom collisions. We review recent theoretical and experimental studies directed at the search for and identification of signatures of dynamic screening and wake effects. Examples include the formation of excited projectile bound states under channeling conditions, radiative electron capture, the search for wake riding'' electrons in antiproton-solid collisions, and the neutralization of highly charged ions near surfaces. 42 refs., 7 figs.

  12. Effects of one night of induced night-wakings versus sleep restriction on sustained attention and mood: a pilot study.

    Science.gov (United States)

    Kahn, Michal; Fridenson, Shimrit; Lerer, Reut; Bar-Haim, Yair; Sadeh, Avi

    2014-07-01

    Despite their high prevalence in daily life, repeated night-wakings and their cognitive and emotional consequences have received less research attention compared to other types of sleep disturbances. Our aim was to experimentally compare the effects of one night of induced infrequent night-wakings (of ∼15 min, each requiring a purposeful response) and sleep restriction on sustained attention and mood in young adults. In a within-between subjects counterbalanced design, 61 healthy adults (40 females; aged 20-29 years) underwent home assessments of sustained attention and self-reported mood at two times: after a normal (control) sleep night, and after a night of either sleep restriction (4h in bed) or induced night-wakings (four prolonged awakenings across 8h in bed). Sleep was monitored using actigraphy and sleep diaries. Sustained attention was assessed using an online continuous performance test (OCPT), and mood was reported online using the Profile of Mood States (POMS). Actigraphic data revealed good compliance with experimental sleep requirements. Induced night-wakings and sleep restriction both resulted in more OCPT omission and commission errors, and in increased depression, fatigue and confusion levels and reduced vigor compared to the normal sleep night. Moreover, there were no significant differences between the consequences of induced awakenings and sleep restriction. Our pilot study indicates that, similar to sleep restriction, one night of life-like repeated night-wakings negatively affects mood and sustained attention. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. Effectiveness of WRF wind direction for retrieving coastal sea surface wind from synthetic aperture radar

    DEFF Research Database (Denmark)

    Takeyama, Yuko; Ohsawa, Teruo; Kozai, Katsutoshi

    2013-01-01

    Wind direction is required as input to the geophysical model function (GMF) for the retrieval of sea surface wind speed from a synthetic aperture radar (SAR) images. The present study verifies the effectiveness of using the wind direction obtained from the weather research and forecasting model...... directions: the meso‐analysis of the Japan Meteorological Agency (MANAL), the SeaWinds microwave scatterometer on QuikSCAT and the National Center for Environmental Prediction final operational global analysis data (NCEP FNL). In comparison with the errors of the SAR‐retrieved wind speeds obtained using...

  14. Effect of aripiprazole on non-24-hour sleep–wake rhythm disorder comorbid with major depressive disorder: a case report

    Directory of Open Access Journals (Sweden)

    Matsui K

    2017-05-01

    Full Text Available Kentaro Matsui,1,2 Yoshikazu Takaesu,2,3 Takeshi Inoue,3 Ken Inada,1 Katsuji Nishimura1 1Department of Psychiatry, Tokyo Women’s Medical University, 2Japan Somnology Center, Neuropsychiatric Research Institute, 3Department of Psychiatry, Tokyo Medical University, Tokyo, Japan Background: Patients with non-24-hour sleep–wake rhythm disorder (N24SWD exhibit a sleep pattern that is asynchronous with the external light–dark cycle, typically involving a cycling, relapsing–remitting pattern of sleep disturbances, including nighttime insomnia and daytime sleepiness. Here, we report the case of a patient with N24SWD comorbid with major depressive disorder, who was successfully treated with a low dose of aripiprazole.Case presentation: A 47-year-old female presented with an 8-year complaint of difficulty falling asleep and waking up in the morning. The patient was diagnosed with major depressive disorder at the age of 35 years and was treated with various antidepressants since that time. At the age of 40 years, the patient’s sleep–wake cycle began to extend without exacerbation of depressive symptoms. The patient was diagnosed with N24SWD at the age of 43 years. Ramelteon 8 mg/d and then melatonin 1 mg/d were administered, but these did not provide effective treatment. In January 2016, after treatment with aripiprazole 3 mg/d in the morning for 4 weeks, the patient’s sleep–wake cycle became markedly synchronized to the environmental light–dark cycle. Her sleep–wake cycle remained synchronized when the same dose of aripiprazole was administered for at least 6 months.Conclusion: Treatment-refractory asynchrony of the sleep–wake cycle in an N24SWD patient with depression was successfully treated with aripiprazole. Although the detailed mechanism of action is unclear, aripiprazole may be an appropriate treatment for patients with circadian rhythm sleep–wake disorders. Keywords: circadian rhythm sleep–wake disorder, non-24

  15. Homeostatic & Circadian Regulation of Wakefulness During Jet Lag and Sleep. Sleep Deprivation: Effect of Wake-Promoting Countermeasures

    National Research Council Canada - National Science Library

    Dinges, David

    2000-01-01

    .... Major human research projects on the effects of induced jet lag and sleep deprivation and their mitigation by sustained low-dose caffeine and naps were undertaken at the University of Pennsylvania...

  16. Wind tunnel evaluation of Hi-Vol TSP effectiveness data

    Data.gov (United States)

    U.S. Environmental Protection Agency — Wind tunnel evaluation of EPA's Hi-Vol TSP sampler for sampling effectiveness with regards to aerodynamic particle diameter (5 to 35 microns), wind speed (2, 8, 24...

  17. ewec 2007 - Europe's premier wind energy event

    International Nuclear Information System (INIS)

    Chaviaropoulos, T.

    2007-01-01

    This online collection of papers - the ewec 2007 proceedings - reflects the various sessions and lectures presented at the ewec wind-energy convention held in Milan in 2007. The first day's sessions looked at the following topics: Renewable Energy Roadmap, the changing structure of the wind industry, politics and programmes, aerodynamics and innovation in turbine design, wind resources and site characterisation (2 sessions), energy scenarios, harmonisation of incentive schemes, structural design and materials, forecasting, integration studies, integrating wind into electricity markets, wind-turbine electrical systems and components, as well as loads, noise and wakes. The second day included sessions on offshore: developments and prospects, extreme wind conditions and forecasting techniques, small wind turbines, distributed generation and autonomous systems cost effectiveness, cost effectiveness of wind energy, financing wind energy concepts, wind and turbulence, wind power plants and grid integration, offshore technology, global challenges and opportunities, aero-elasticity, loads and control, operations and maintenance, carbon trading and the emission trading schemes, investment strategies of power producers, wind power plants and grid integration, wind turbine electrical systems and components, and wakes. The third day offered sessions on environmental issues, condition monitoring, operation and maintenance, structural design and materials, the Up-Wind workshop, winning hearts and minds, offshore technology, advances in measuring methods and advancing drive-train reliability. In a closing session the conference was summarised, awards for poster contributions were made and the Poul la Cour Prize was presented

  18. Reliability Analysis of Wind Turbines

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Sørensen, John Dalsgaard

    2008-01-01

    In order to minimise the total expected life-cycle costs of a wind turbine it is important to estimate the reliability level for all components in the wind turbine. This paper deals with reliability analysis for the tower and blades of onshore wind turbines placed in a wind farm. The limit states...... consideres are in the ultimate limit state (ULS) extreme conditions in the standstill position and extreme conditions during operating. For wind turbines, where the magnitude of the loads is influenced by the control system, the ultimate limit state can occur in both cases. In the fatigue limit state (FLS......) the reliability level for a wind turbine placed in a wind farm is considered, and wake effects from neighbouring wind turbines is taken into account. An illustrative example with calculation of the reliability for mudline bending of the tower is considered. In the example the design is determined according...

  19. The dune effect on sand-transporting winds on Mars

    Science.gov (United States)

    Jackson, Derek W. T.; Bourke, Mary C.; Smyth, Thomas A. G.

    2015-11-01

    Wind on Mars is a significant agent of contemporary surface change, yet the absence of in situ meteorological data hampers the understanding of surface-atmospheric interactions. Airflow models at length scales relevant to landform size now enable examination of conditions that might activate even small-scale bedforms (ripples) under certain contemporary wind regimes. Ripples have the potential to be used as modern `wind vanes' on Mars. Here we use 3D airflow modelling to demonstrate that local dune topography exerts a strong influence on wind speed and direction and that ripple movement likely reflects steered wind direction for certain dune ridge shapes. The poor correlation of dune orientation with effective sand-transporting winds suggests that large dunes may not be mobile under modelled wind scenarios. This work highlights the need to first model winds at high resolution before inferring regional wind patterns from ripple movement or dune orientations on the surface of Mars today.

  20. Comparative study of the behavior of wind-turbines in a wind farm

    Energy Technology Data Exchange (ETDEWEB)

    Migoya, Emilio; Crespo, Antonio; Garcia, Javier; Manuel, Fernando; Jimenez, Angel [Universidad Politecnica de Madrid (UPM), Madrid (Spain). Departamento de Ingenieria Energetica y Fluidomecanica, Laboratorio de Mecanica de Fluidos; Moreno, Fermin [Comision Nacional de la Energia, Madrid (Spain); Costa, Alexandre [Energia Eolica, Division de Energias Renovables, CIEMAT, Madrid (Spain)

    2007-10-15

    The Sotavento wind farm is an experimental wind farm which has different types of wind turbines. It is located in an area whose topography is moderately complex, and where wake effects can be significant. One of the objectives of Sotavento wind farm is to compare the performances of the different machines; particularly regarding power production, maintenance and failures. However, because of wakes and topography, the different machines are not working under identical conditions. Two linearized codes have been used to estimate topography effects: UPMORO and WAsP. For wind directions in which topography is abrupt, the non-linear flow equations have been solved with the commercial code FLUENT, although the results are only qualitatively used. For wake effects, the UPMPARK code has been applied. As a result, the incident velocity over each wind turbine is obtained, and the power production is estimated by means of the power curve of each machine. Experimental measurements give simultaneously the wind characteristics at the measuring stations, the wind velocity, at the nacelle anemometer, and the power production of each wind turbine. These experimental results are employed to validate the numerical predictions. The main objective of this work is to deduce and validate a relationship between the wind characteristics measured in the anemometers and the wind velocity and the power output in each machine. (author)

  1. Direct Numerical Simulation of a Temporally Evolving Incompressible Plane Wake: Effect of Initial Conditions on Evolution and Topology

    Science.gov (United States)

    Sondergaard, R.; Cantwell, B.; Mansour, N.

    1997-01-01

    Direct numerical simulations have been used to examine the effect of the initial disturbance field on the development of three-dimensionality and the transition to turbulence in the incompressible plane wake. The simulations were performed using a new numerical method for solving the time-dependent, three-dimensional, incompressible Navier-Stokes equations in flows with one infinite and two periodic directions. The method uses standard Fast Fourier Transforms and is applicable to cases where the vorticity field is compact in the infinite direction. Initial disturbances fields examined were combinations of two-dimensional waves and symmetric pairs of 60 deg oblique waves at the fundamental, subharmonic, and sub-subharmonic wavelengths. The results of these simulations indicate that the presence of 60 deg disturbances at the subharmonic streamwise wavelength results in the development of strong coherent three-dimensional structures. The resulting strong three-dimensional rate-of-strain triggers the growth of intense fine scale motions. Wakes initiated with 60 deg disturbances at the fundamental streamwise wavelength develop weak coherent streamwise structures, and do not develop significant fine scale motions, even at high Reynolds numbers. The wakes which develop strong three-dimensional structures exhibit growth rates on par with experimentally observed turbulent plane wakes. Wakes which develop only weak three-dimensional structures exhibit significantly lower late time growth rates. Preliminary studies of wakes initiated with an oblique fundamental and a two-dimensional subharmonic, which develop asymmetric coherent oblique structures at the subharmonic wavelength, indicate that significant fine scale motions only develop if the resulting oblique structures are above an angle of approximately 45 deg.

  2. Differential effects of midazolam and zolpidem on sleep-wake states and epileptic activity in WAG/Rij rats

    NARCIS (Netherlands)

    Depoortere, H.; Francon, D.; Luijtelaar, E.L.J.M. van; Drinkenburg, W.H.I.M.; Coenen, A.M.L.

    1995-01-01

    Hypnotic drugs are known to possess antiepileptic activity. Therefore, the effects of the benzodiazepine hypnotic midazolam (10 mg/kg) and the novel imidazopyridine hypnotic zolpidem (10 mg/kg) on sleep-wake states and on the number of spike-wave discharges were evaluated in WAG/Rij rats. Rats of

  3. The effects of diurnal intermittent fasting on the wake-promoting neurotransmitter orexin-A

    Science.gov (United States)

    Almeneessier, Aljohara S.; Alzoghaibi, Mohammed; BaHammam, Abdulrahman A.; Ibrahim, Mahmoud G.; Olaish, Awad H.; Nashwan, Samar Z.; BaHammam, Ahmed S.

    2018-01-01

    BACKGROUND: Food restriction has been demonstrated to increase the alertness in different species and to increase the levels of the wake-promoting neurotransmitter orexin. We hypothesized that diurnal intermittent fasting (DIF) increases orexin-A levels during fasting. Therefore, we conducted this study to assess the effects of DIF, during the month of Ramadan, on orexin, while controlling for lifestyle changes that may accompany Ramadan such as sleep duration, bedtime and wake time, energy expenditure, light exposure, and food. METHODS: Eight young healthy volunteers (mean age, 25.4 ± 3.5 years) reported to the laboratory on three occasions: (1) 4 weeks before Ramadan while performing DIF for 1 week outside the month of Ramadan (fasting outside Ramadan); (2) 1 week before Ramadan (nonfasting baseline) (BL); and (3) during the 2nd week of Ramadan while performing DIF (Ramadan). Plasma levels of orexin-A were measured using an enzyme immunoassay five times at 22:00, 02:00, 04:00, 06:00, and 11:00. Caloric intake, light exposure, and sleep schedule were maintained during the participants’ stays in the laboratory in the three study periods. RESULTS: Orexin-A levels increased in the daytime during fasting and decreased at night compared to BL. The differences in orexin-A levels between DIF and BL were significant at 06:00, 11:00, 22:00, and 02:00. CONCLUSIONS: DIF increases orexin-A levels in the plasma during fasting hours. This finding supports findings from animal studies showing that fasting increases alertness. PMID:29387256

  4. Evaluation of the Effect of Nest Posture on the Sleep-wake State of Premature Infants

    Directory of Open Access Journals (Sweden)

    Tayebeh Reyhani

    2016-04-01

    Full Text Available Background: Premature birth is a major cause of infant mortality in developed countries. Newborns confined to neonatal intensive care units (NICUs are in a rapid stage of brain development. As such, sleep plays a pivotal role in the proper brain development of newborns. However, this developmental aspect is often disregarded due to the lack of information. Aim: This study aimed to evaluate the effect of nest posture on the sleep-wake state of premature infants. Method: This cross-over clinical trial was conducted on 60 premature infants admitted in the NICU of Ghaem Hospital in Mashhad, Iran in 2015. Infants were divided into two groups of experimental and control. Data were collected using the Assessment of Premature Infants' Behavior (APIB. Neonates in the control group were placed in an incubator, and neonates in the experimental group were positioned in a nest. Between-group comparison was performed using paired-samples T-test for normal variables and Wilcoxon test for non-normal variables. Results: In this study, no statistically significant differences were observed between the two groups in terms of the scores of deep sleep state before (P=0.50 and after the intervention (P=0.59. However, during the intervention, mean score of deep sleep was higher in the experimental group (P=0.08. Moreover, mean score of slow wake state had no significant difference between the study groups before (P=0.67, after (P=0.86, and during the intervention (P=0.81. Implications for Practice: According to the results of this study, nest posture increased the deep sleep hours of premature infants as the most imperative state of brain development. Therefore, it is recommended that nest posture be used to improve the deep sleep state of premature infants.

  5. The effects of diurnal intermittent fasting on the wake-promoting neurotransmitter orexin-A.

    Science.gov (United States)

    Almeneessier, Aljohara S; Alzoghaibi, Mohammed; BaHammam, Abdulrahman A; Ibrahim, Mahmoud G; Olaish, Awad H; Nashwan, Samar Z; BaHammam, Ahmed S

    2018-01-01

    Food restriction has been demonstrated to increase the alertness in different species and to increase the levels of the wake-promoting neurotransmitter orexin. We hypothesized that diurnal intermittent fasting (DIF) increases orexin-A levels during fasting. Therefore, we conducted this study to assess the effects of DIF, during the month of Ramadan, on orexin, while controlling for lifestyle changes that may accompany Ramadan such as sleep duration, bedtime and wake time, energy expenditure, light exposure, and food. Eight young healthy volunteers (mean age, 25.4 ± 3.5 years) reported to the laboratory on three occasions: (1) 4 weeks before Ramadan while performing DIF for 1 week outside the month of Ramadan (fasting outside Ramadan); (2) 1 week before Ramadan (nonfasting baseline) (BL); and (3) during the 2 nd week of Ramadan while performing DIF (Ramadan). Plasma levels of orexin-A were measured using an enzyme immunoassay five times at 22:00, 02:00, 04:00, 06:00, and 11:00. Caloric intake, light exposure, and sleep schedule were maintained during the participants' stays in the laboratory in the three study periods. Orexin-A levels increased in the daytime during fasting and decreased at night compared to BL. The differences in orexin-A levels between DIF and BL were significant at 06:00, 11:00, 22:00, and 02:00. DIF increases orexin-A levels in the plasma during fasting hours. This finding supports findings from animal studies showing that fasting increases alertness.

  6. Distinctive effects of modafinil and d-amphetamine on the homeostatic and circadian modulation of the human waking EEG.

    Science.gov (United States)

    Chapotot, Florian; Pigeau, Ross; Canini, Frédéric; Bourdon, Lionel; Buguet, Alain

    2003-03-01

    Modafinil is a wake-promoting agent that affects hypothalamic structures involved in the homeostatic and circadian regulation of vigilance. Administered during sleep deprivation, it reduces the need for prolonged recovery sleep and decreases the rebound in EEG slow-wave activity. These diachronic effects suggest an action of modafinil on a homeostatic sleep regulatory process. The aim of this study was to determine whether modafinil, in comparison to the d-amphetamine reference psychostimulant and to placebo, interferes with the vigilance regulatory processes reflected in the EEG during waking. Thirty-three healthy subjects were investigated during 60 h of sustained wakefulness in a double-blind placebo-controlled parallel-design study. A 4-min maintenance-of-wakefulness test administered hourly allowed the concomitant assessment of alertness and waking EEG activity. The effects of equipotent psychostimulant dosages (modafinil 300 mg and d-amphetamine 20 mg) were evaluated at the beginning of the first sleep deprivation night, at the end of the second sleep deprivation night and in the afternoon preceding the first recovery night. One hour following ingestion, both psychostimulants increased alertness during 10-12 h, independently of the time of administration. At the level of the waking EEG, d-amphetamine attenuated the natural circadian rhythm of the different frequency bands and suppressed the sleep deprivation-related increase in low frequency (0.5-7 Hz) powers. In contrast, modafinil, which exhibited a transient amphetamine-like effect, had slight effect on circadian rhythms. Its selective action was characterized by maintenance of the alpha(1) (8.5-11.5 Hz) EEG power, which under placebo exhibited a homeostatic decrease paralleling that of alertness with a circadian trough at night. These findings demonstrate that the alertness-promoting effects of modafinil and d-amphetamine involve distinct EEG activities and do not reside on the same vigilance regulatory

  7. Temperature Effects on the Wind Direction Measurement of 2D Solid Thermal Wind Sensors

    Science.gov (United States)

    Chen, Bei; Zhu, Yan-Qing; Yi, Zhenxiang; Qin, Ming; Huang, Qing-An

    2015-01-01

    For a two-dimensional solid silicon thermal wind sensor with symmetrical structure, the wind speed and direction information can be derived from the output voltages in two orthogonal directions, i.e., the north-south and east-west. However, the output voltages in these two directions will vary linearly with the ambient temperature. Therefore, in this paper, a temperature model to study the temperature effect on the wind direction measurement has been developed. A theoretical analysis has been presented first, and then Finite Element Method (FEM) simulations have been performed. It is found that due to symmetrical structure of the thermal wind sensor, the temperature effects on the output signals in the north-south and east-west directions are highly similar. As a result, the wind direction measurement of the thermal wind sensor is approximately independent of the ambient temperature. The experimental results fit the theoretical analysis and simulation results very well. PMID:26633398

  8. Wake fields effects due to surface roughness in a circular pipe

    CERN Document Server

    Angelici, M; Mostacci, A; Palumbo, L

    2001-01-01

    The problem of the wake field generated by a relativistic particle travelling in a long beam pipe with rough surface has been studied by means of a standard theory based on the hybrid modes excited in a periodically corrugated waveguide with circular cross-section. Slow waves synchronous with the particle can be excited in the structure, producing wake fields whose frequency and amplitude depend on the depth of the corrugation. An analytical expression of the wake field is given for very small corrugations.

  9. Downstream wind flow path diversion and its effects on the performance of vertical axis wind turbine

    International Nuclear Information System (INIS)

    Maganhar, A.L.

    2015-01-01

    In the present experimental study efforts have been made to analysis path diversion effect of downstream wind flow on performance of vertical axis wind turbine (VAWT). For the blockage of downstream wind flow path at various linear displaced positions, a normal erected flat wall, semi-circular and cylindrical shapes were tested for path diverting geometries. Performance of VAWT in terms of improved rotor speed up to 45% was achieved. (author)

  10. Health effects related to wind turbine noise exposure

    DEFF Research Database (Denmark)

    Schmidt, Jesper Hvass; Klokker, Mads

    2014-01-01

    BACKGROUND: Wind turbine noise exposure and suspected health-related effects thereof have attracted substantial attention. Various symptoms such as sleep-related problems, headache, tinnitus and vertigo have been described by subjects suspected of having been exposed to wind turbine noise...... existing statistically-significant evidence indicating any association between wind turbine noise exposure and tinnitus, hearing loss, vertigo or headache. LIMITATIONS: Selection bias and information bias of differing magnitudes were found to be present in all current studies investigating wind turbine...

  11. Optimization Under Uncertainty for Wake Steering Strategies

    Energy Technology Data Exchange (ETDEWEB)

    Quick, Julian [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Annoni, Jennifer [National Renewable Energy Laboratory (NREL), Golden, CO (United States); King, Ryan N [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Dykes, Katherine L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Fleming, Paul A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Ning, Andrew [Brigham Young University

    2017-08-03

    Offsetting turbines' yaw orientations from incoming wind is a powerful tool that may be leveraged to reduce undesirable wake effects on downstream turbines. First, we examine a simple two-turbine case to gain intuition as to how inflow direction uncertainty affects the optimal solution. The turbines are modeled with unidirectional inflow such that one turbine directly wakes the other, using ten rotor diameter spacing. We perform optimization under uncertainty (OUU) via a parameter sweep of the front turbine. The OUU solution generally prefers less steering. We then do this optimization for a 60-turbine wind farm with unidirectional inflow, varying the degree of inflow uncertainty and approaching this OUU problem by nesting a polynomial chaos expansion uncertainty quantification routine within an outer optimization. We examined how different levels of uncertainty in the inflow direction effect the ratio of the expected values of deterministic and OUU solutions for steering strategies in the large wind farm, assuming the directional uncertainty used to reach said OUU solution (this ratio is defined as the value of the stochastic solution or VSS).

  12. Caffeine administration at night during extended wakefulness effectively mitigates performance impairment but not subjective assessments of fatigue and sleepiness.

    Science.gov (United States)

    Paech, Gemma M; Banks, Siobhan; Pajcin, Maja; Grant, Crystal; Johnson, Kayla; Kamimori, Gary H; Vedova, Chris B Della

    2016-06-01

    The current study investigated the effects of repeated caffeine administration on performance and subjective reports of sleepiness and fatigue during 50h extended wakefulness. Twenty-four, non-smokers aged 22.5±2.9y (mean±SD) remained awake for two nights (50h) in a controlled laboratory environment. During this period, 200mg of caffeine or placebo gum was administered at 01:00, 03:00, 05:00 and 07:00 on both nights (total of 800mg/night). Neurobehavioral performance and subjective reports were assessed throughout the wake period. Caffeine improved performance compared to placebo, but did not affect overall ratings of subjective sleepiness and fatigue. Performance and sleepiness worsened with increasing time awake for both conditions. However, caffeine slowed performance impairments such that after 50h of wakefulness performance was better following caffeine administration compared to placebo. Caffeine also slowed the increase in subjective sleepiness and performance ratings, but only during the first night of wakefulness. After two nights of sleep deprivation, there was no difference in sleepiness ratings between the two conditions. These results demonstrate that strategic administration of caffeine effectively mitigates performance impairments associated with 50h wakefulness but does not improve overall subjective assessments of sleepiness, fatigue and performance. Results indicate that while performance impairment is alleviated, individuals may continue to report feelings of sleepiness. Individuals who use caffeine as a countermeasure in sustained operations may feel as though caffeine is not effective despite impairments in objective performance being largely mitigated. Copyright © 2016 Elsevier Inc. All rights reserved.

  13. Effect of wind turbine surge motion on rotor thrust and induced velocity

    DEFF Research Database (Denmark)

    Vaal, J.B., de; Hansen, Martin Otto Laver; Moan, T.

    2014-01-01

    velocity on a wind turbine rotor is investigated. Specifically, the performance of blade element momentum theory with a quasisteady wake as well as two widely used engineering dynamic inflow models is evaluated. A moving actuator disc model is used as reference, since the dynamics associated with the wake...... will be inherently included in the solution of the associated fluid dynamic problem. Through analysis of integrated rotor loads, induced velocities and aerodynamic damping, it is concluded that typical surge motions are sufficiently slow to not affect the wake dynamics predicted by engineering models significantly...

  14. Reducing Turbine Mechanical Loads Using Flow Model-Based Wind Farm Controller

    DEFF Research Database (Denmark)

    Kazda, Jonas; Cutululis, Nicolaos Antonio

    WindFarm [2]. SimWindFarm allows for the simultaneous simulation of the turbulent hub height flow field in the wind farm, the turbine dynamics and the wind farm control. The tests show a reduction of loads when compared to other optimal wind farm control approaches. Future work shall enhance the controller......Cumulated O&M costs of offshore wind farms are comparable with wind turbine CAPEX of such wind farm. In wind farms, wake effects can result in up to 80% higher fatigue loads at downstream wind turbines [1] and consequently larger O&M costs. The present work therefore investigates to reduce...... these loads during the provision of grid balancing services using optimal model-based wind farm control. Wind farm controllers coordinate the operating point of wind turbines in a wind farm in order to achieve a given objective. The investigated objective of the control in this work is to follow a total wind...

  15. A Novel Energy Yields Calculation Method for Irregular Wind Farm Layout

    DEFF Research Database (Denmark)

    Hou, Peng; Hu, Weihao; Soltani, Mohsen

    2015-01-01

    Due to the increasing size of offshore wind farm, the impact of the wake effect on energy yields become more and more evident. The Seafloor topography would limit the layout of the wind farm so that irregular layout is usually adopted inlarge scale offshore wind farm. However, the calculation...

  16. Effects of acute systemic administration of cannabidiol on sleep-wake cycle in rats.

    Science.gov (United States)

    Chagas, Marcos Hortes N; Crippa, José Alexandre S; Zuardi, Antonio Waldo; Hallak, Jaime E C; Machado-de-Sousa, João Paulo; Hirotsu, Camila; Maia, Lucas; Tufik, Sergio; Andersen, Monica Levy

    2013-03-01

    Cannabidiol (CBD) is one of the main components of Cannabis sativa and has a wide spectrum of action, including effects in the sleep-wake cycle. The objective of this paper is to assess the effects on sleep of acute systemic administration of CBD. Adult male Wistar rats were randomly distributed into four groups that received intraperitoneal injections of CBD 2.5 mg/kg, CBD 10 mg/kg, CBD 40 mg/kg or vehicle (n=seven animals/group). Sleep recordings were made during light and dark periods for four days: two days of baseline recording, one day of drug administration (test), and one day after drug (post-test). During the light period of the test day, the total percentage of sleep significantly increased in the groups treated with 10 and 40 mg/kg of CBD compared to placebo. REM sleep latency increased in the group injected with CBD 40 mg/kg and was significantly decreased with the dose of 10 mg/kg on the post-test day. There was an increase in the time of SWS in the group treated with CBD 40 mg/kg, although this result did not reach statistical significance. The systemic acute administration of CBD appears to increase total sleep time, in addition to increasing sleep latency in the light period of the day of administration.

  17. Dissociating Effects of Global SWS Disruption and Healthy Aging on Waking Performance and Daytime Sleepiness

    Science.gov (United States)

    Groeger, John A.; Stanley, Neil; Deacon, Stephen; Dijk, Derk-Jan

    2014-01-01

    Study Objective: To contrast the effects of slow wave sleep (SWS) disruption and age on daytime functioning. Design: Daytime functioning was contrasted in three age cohorts, across two parallel 4-night randomized groups (baseline, two nights of SWS disruption or control, recovery sleep). Setting: Sleep research laboratory. Participants: 44 healthy young (20-30 y), 35 middle-aged (40-55 y), and 31 older (66-83 y) men and women. Interventions: Acoustic stimulation contingent on appearance of slow waves. Measurements and Results: Cognitive performance was assessed before sleep latency tests at five daily time-points. SWS disruption resulted in less positive affect, slower or impaired information processing and sustained attention, less precise motor control, and erroneous implementation, rather than inhibition, of well-practiced actions. These performance impairments had far smaller effect sizes than the increase in daytime sleepiness and differed from baseline to the same extent for each age group. At baseline, younger participants performed better than older participants across many cognitive domains, with largest effects on executive function, response time, sustained attention, and motor control. At baseline, the young were sleepier than other age groups. Conclusions: SWS has been considered a potential mediator of age-related decline in performance, although the effects of SWS disruption on daytime functioning have not been quantified across different cognitive domains nor directly compared to age-related changes in performance. The data imply that two nights of SWS disruption primarily leads to an increase in sleepiness with minor effects on other aspects of daytime functioning, which are different from the substantial effects of age. Citation: Groeger JA, Stanley N, Deacon S, Dijk DJ. Dissociating effects of global sws disruption and healthy aging on waking performance and daytime sleepiness. SLEEP 2014;37(6):1127-1142. PMID:24882908

  18. Efficient Turbulence Modeling for CFD Wake Simulations

    DEFF Research Database (Denmark)

    van der Laan, Paul

    , that can accurately and efficiently simulate wind turbine wakes. The linear k-ε eddy viscosity model (EVM) is a popular turbulence model in RANS; however, it underpredicts the velocity wake deficit and cannot predict the anisotropic Reynolds-stresses in the wake. In the current work, nonlinear eddy...... viscosity models (NLEVM) are applied to wind turbine wakes. NLEVMs can model anisotropic turbulence through a nonlinear stress-strain relation, and they can improve the velocity deficit by the use of a variable eddy viscosity coefficient, that delays the wake recovery. Unfortunately, all tested NLEVMs show...... numerically unstable behavior for fine grids, which inhibits a grid dependency study for numerical verification. Therefore, a simpler EVM is proposed, labeled as the k-ε - fp EVM, that has a linear stress-strain relation, but still has a variable eddy viscosity coefficient. The k-ε - fp EVM is numerically...

  19. Estimation of Rotor Effective Wind Speed: A Comparison

    DEFF Research Database (Denmark)

    Soltani, Mohsen; Knudsen, Torben; Svenstrup, Mikael

    2013-01-01

    Modern wind turbine controllers use wind speed information to improve power production and reduce loads on the turbine components. The turbine top wind speed measurement is unfortunately imprecise and not a good representative of the rotor effective wind speed. Consequently, many different model......-based algorithms have been proposed that are able to estimate the wind speed using common turbine measurements. In this paper, we present a concise yet comprehensive analysis and comparison of these techniques, reviewing their advantages and drawbacks. We implement these techniques and compare the results on both...

  20. Effect of Fin Porosity on Wake Geometry for Flapping Fins at Intermediate Reynolds Number

    Science.gov (United States)

    Chen, J.; Xia, B.; Krueger, P. S.

    2017-11-01

    Low aspect ratio flapping fins generate interesting 3-dimensional flow structures as has been observed, for example, in studies of fish swimming. As the Reynolds number is reduced, the exact geometry of the fin is less important and even certain amounts of porosity might be allowed without significantly affecting propulsive performance. These effects are investigated experimentally using flapping rectangular fins of aspect ratio 2 at Reynolds numbers in the range 100 - 1000. The experiments were conducted using a water tunnel to supply the free stream flow and the fin flapping parameters were set to provide a Strouhal number (based on amplitude of the fin tip motion) in the range 0.15 - 0.35. Phase-averaged measurements were made of the 3-dimensional, volumetric flow field, allowing visualization of the typical shed vortex structure behind the fin and calculation of time averaged thrust and propulsive efficiency. Results comparing the flow structure in the fin wake and the resulting propulsive performance will be presented for several fins with different planform porosities where the porosities are set using arrays of holes in the fins. This material is based on the work supported by the National Science Foundation under Grant No. 1510707.

  1. Modeling the Cost Effectiveness of Neuroimaging-Based Treatment of Acute Wake-Up Stroke.

    Directory of Open Access Journals (Sweden)

    Ankur Pandya

    Full Text Available Thrombolytic treatment (tissue-type plasminogen activator [tPA] is only recommended for acute ischemic stroke patients with stroke onset time 4.5 hours, 46.3% experienced a good stroke outcome. Lifetime discounted QALYs and costs were 5.312 and $88,247 for the no treatment strategy and 5.342 and $90,869 for the MRI-based strategy, resulting in an ICER of $88,000/QALY. Results were sensitive to variations in patient- and provider-specific factors such as sleep duration, hospital travel and door-to-needle times, as well as onset probability distribution, MRI specificity, and mRS utility values.Our model-based findings suggest that an MRI-based treatment strategy for this population could be cost-effective and quantifies the impact that patient- and provider-specific factors, such as sleep duration, hospital travel and door-to-needle times, could have on the optimal decision for wake-up stroke patients.

  2. Dreamlike effects of LSD on waking imagery in humans depend on serotonin 2A receptor activation.

    Science.gov (United States)

    Kraehenmann, Rainer; Pokorny, Dan; Vollenweider, Leonie; Preller, Katrin H; Pokorny, Thomas; Seifritz, Erich; Vollenweider, Franz X

    2017-07-01

    Accumulating evidence indicates that the mixed serotonin and dopamine receptor agonist lysergic acid diethylamide (LSD) induces an altered state of consciousness that resembles dreaming. This study aimed to test the hypotheses that LSD produces dreamlike waking imagery and that this imagery depends on 5-HT2A receptor activation and is related to subjective drug effects. Twenty-five healthy subjects performed an audiorecorded guided mental imagery task 7 h after drug administration during three drug conditions: placebo, LSD (100 mcg orally) and LSD together with the 5-HT2A receptor antagonist ketanserin (40 mg orally). Cognitive bizarreness of guided mental imagery reports was quantified as a standardised formal measure of dream mentation. State of consciousness was evaluated using the Altered State of Consciousness (5D-ASC) questionnaire. LSD, compared with placebo, significantly increased cognitive bizarreness (p LSD-induced increase in cognitive bizarreness was positively correlated with the LSD-induced loss of self-boundaries and cognitive control (p LSD-induced increases in cognitive bizarreness and changes in state of consciousness were fully blocked by ketanserin. LSD produced mental imagery similar to dreaming, primarily via activation of the 5-HT2A receptor and in relation to loss of self-boundaries and cognitive control. Future psychopharmacological studies should assess the differential contribution of the D2/D1 and 5-HT1A receptors to cognitive bizarreness.

  3. Comparison of Engineering Wake Models with CFD Simulations

    DEFF Research Database (Denmark)

    Andersen, Søren Juhl; Sørensen, Jens Nørkær; Ivanell, S.

    2014-01-01

    The engineering wake models by Jensen [1] and Frandsen et al. [2] are assessed for different scenarios simulated using Large Eddy Simulation and the Actuator Line method implemented in the Navier-Stokes equations. The scenarios include the far wake behind a single wind turbine, a long row...... of turbines in an atmospheric boundary layer, idealised cases of an infinitely long row of wind turbines and infinite wind farms with three different spacings. Both models include a wake expansion factor, which is calibrated to fit the simulated wake velocities. The analysis highlights physical deficiencies...

  4. Data-driven wind plant control

    NARCIS (Netherlands)

    Gebraad, P.M.O.

    2014-01-01

    Each wind turbine in a cluster of wind turbines (a wind power plant) can influence the performance of other turbines through the wake that forms downstream of its rotor. The wake has a reduced wind velocity, since the turbine extracts energy from the flow, and the obstruction by the wind turbine

  5. Wake-up effects in Si-doped hafnium oxide ferroelectric thin films

    International Nuclear Information System (INIS)

    Zhou, Dayu; Xu, Jin; Li, Qing; Guan, Yan; Cao, Fei; Dong, Xianlin; Müller, Johannes; Schenk, Tony; Schröder, Uwe

    2013-01-01

    Hafnium oxide based ferroelectric thin films have shown potential as a promising alternative material for non-volatile memory applications. This work reports the switching stability of a Si-doped HfO 2 film under bipolar pulsed-field operation. High field cycling causes a “wake-up” in virgin “pinched” polarization hysteresis loops, demonstrated by an enhancement in remanent polarization and a shift of negative coercive voltage. The rate of wake-up is accelerated by either reducing the frequency or increasing the amplitude of the cycling field. We suggest de-pinning of domains due to reduction of the defect concentration at bottom electrode interface as origin of the wake-up

  6. Health effects and wind turbines: A review of the literature

    OpenAIRE

    Ollson Christopher A; Knopper Loren D

    2011-01-01

    Abstract Background Wind power has been harnessed as a source of power around the world. Debate is ongoing with respect to the relationship between reported health effects and wind turbines, specifically in terms of audible and inaudible noise. As a result, minimum setback distances have been established world-wide to reduce or avoid potential complaints from, or potential effects to, people living in proximity to wind turbines. People interested in this debate turn to two sources of informat...

  7. Multiple vortex structures in the wake of a rectangular winglet in ground effect

    DEFF Research Database (Denmark)

    Velte, Clara Marika; Hansen, Martin Otto Laver; Okulov, Valery L.

    2016-01-01

    Patterns of vorticity in the wake of a single rectangular winglet (vortex generator) embedded in a turbulent boundary layer have been studied using Stereoscopic Particle Image Velocimetry (SPIV). The winglet was mounted normally to a flat surface with an angle to the oncoming flow. A parametric...... study varying the winglet height (constant aspect ratio) and angle has shown, contrary to the common classical single tip-vortex conception, that the wake generally consists of a complex system of multiple vortex structures. The primary vortex has previously been discovered to contain a direct coupling...

  8. Gravity effects on wind-induced flutter of leaves

    Science.gov (United States)

    Clemmer, Nickalaus; Kopperstad, Karsten; Solano, Tomas; Shoele, Kourosh; Ordonez, Juan

    2017-11-01

    Wind-Induced flutter of leaves depends on both wind velocity and the gravity. To study the gravitational effects on the oscillatory behavior of leaves in the wind, a wind tunnel that can be tilted about the center of the test section is created. This unique rotation capability allows systematic investigation of gravitational effects on the fluttering response of leaves. The flow-induced vibration will be studied for three different leaves at several different tilting angles including the wind travels horizontally, vertically downward and vertically upward. In each situation, the long axis of a leaf is placed parallel to the wind direction and its response is studied at different flow speed. Oscillation of the leaf is recorded via high-speed camera at each of setup, and the effect of the gravity on stabilizing or destabilizing the fluttering response is investigated. Summer REU student at Florida State University.

  9. A Comparison Study of a Generic Coupling Methodology for Modeling Wake Effects of Wave Energy Converter Arrays

    Directory of Open Access Journals (Sweden)

    Tim Verbrugghe

    2017-10-01

    Full Text Available Wave Energy Converters (WECs need to be deployed in large numbers in an array layout in order to have a significant power production. Each WEC has an impact on the incoming wave field, by diffracting, reflecting and radiating waves. Simulating the wave transformations within and around a WEC array is complex; it is difficult, or in some cases impossible, to simulate both these near-field and far-field wake effects using a single numerical model, in a time- and cost-efficient way in terms of computational time and effort. Within this research, a generic coupling methodology is developed to model both near-field and far-field wake effects caused by floating (e.g., WECs, platforms or fixed offshore structures. The methodology is based on the coupling of a wave-structure interaction solver (Nemoh and a wave propagation model. In this paper, this methodology is applied to two wave propagation models (OceanWave3D and MILDwave, which are compared to each other in a wide spectrum of tests. Additionally, the Nemoh-OceanWave3D model is validated by comparing it to experimental wave basin data. The methodology proves to be a reliable instrument to model wake effects of WEC arrays; results demonstrate a high degree of agreement between the numerical simulations with relative errors lower than 5 % and to a lesser extent for the experimental data, where errors range from 4 % to 17 % .

  10. Wind Farm Active Power Dispatch for Output Power Maximizing Based on a Wind Turbine Control Strategy for Load Minimizing

    DEFF Research Database (Denmark)

    Zhang, Baohua; Hu, Weihao; Hou, Peng

    2015-01-01

    Inclusion of the wake effect in the wind farm control design (WF) can increase the total captured power by wind turbines (WTs), which is usually implemented by derating upwind WTs. However, derating the WT without a proper control strategy will increase the structural loads, caused by operation i...

  11. Effects of caffeine on daytime recovery sleep: A double challenge to the sleep-wake cycle in aging.

    Science.gov (United States)

    Carrier, Julie; Paquet, Jean; Fernandez-Bolanos, Marta; Girouard, Laurence; Roy, Joanie; Selmaoui, Brahim; Filipini, Daniel

    2009-10-01

    Caffeine is the most widely used stimulant to counteract the effects of sleepiness, but it also produces important detrimental effects on subsequent sleep, especially when sleep is initiated at a time when the biological clock sends a strong waking signal such as during daytime. This study compares the effects of caffeine on daytime recovery sleep in young (20-30 y.) and middle-aged subjects (45-60 y.). Subjects participated in both caffeine (200mg) and placebo conditions (double-blind cross-over design), spaced one month apart. For each condition, subjects initially came to the laboratory for a nocturnal sleep episode. Daytime recovery sleep started in the morning after 25h of wakefulness. Subjects were administered either one caffeine (100mg) or placebo capsule three hours before daytime recovery sleep and the remaining dose one hour before daytime recovery sleep. Middle-aged subjects showed greater decrements of sleep duration and sleep efficiency than young subjects during daytime recovery under placebo compared to nocturnal sleep. Caffeine decreased sleep efficiency, sleep duration, slow-wave sleep (SWS) and REM sleep during daytime recovery sleep similarly in both age groups. Caffeine also reduced N-REM sleep EEG synchronization during daytime recovery sleep (reduced delta, theta, and alpha power, and greater beta power). The combined influence of age and caffeine made the sleep of middle-aged subjects particularly vulnerable to the circadian waking signal. We propose that lower brain synchronization due to age and caffeine produces greater difficulty in overriding the circadian waking signal during daytime sleep and leads to fragmented sleep. These results have implications for the high proportion of the population using caffeine to cope with night work and jet lag, particularly the middle-aged.

  12. Study of Wind Effects on Unique Buildings

    Science.gov (United States)

    Olenkov, V.; Puzyrev, P.

    2017-11-01

    The article deals with a numerical simulation of wind effects on the building of the Church of the Intercession of the Holy Virgin in the village Bulzi of the Chelyabinsk region. We presented a calculation algorithm and obtained pressure fields, velocity fields and the fields of kinetic energy of a wind stream, as well as streamlines. Computational fluid dynamic (CFD) evolved three decades ago at the interfaces of calculus mathematics and theoretical hydromechanics and has become a separate branch of science the subject of which is a numerical simulation of different fluid and gas flows as well as the solution of arising problems with the help of methods that involve computer systems. This scientific field which is of a great practical value is intensively developing. The increase in CFD-calculations is caused by the improvement of computer technologies, creation of multipurpose easy-to-use CFD-packagers that are available to a wide group of researchers and cope with various tasks. Such programs are not only competitive in comparison with physical experiments but sometimes they provide the only opportunity to answer the research questions. The following advantages of computer simulation can be pointed out: a) Reduction in time spent on design and development of a model in comparison with a real experiment (variation of boundary conditions). b) Numerical experiment allows for the simulation of conditions that are not reproducible with environmental tests (use of ideal gas as environment). c) Use of computational gas dynamics methods provides a researcher with a complete and ample information that is necessary to fully describe different processes of the experiment. d) Economic efficiency of computer calculations is more attractive than an experiment. e) Possibility to modify a computational model which ensures efficient timing (change of the sizes of wall layer cells in accordance with the chosen turbulence model).

  13. Effects of nocturnal hemodialysis on melatonin rhythm and sleep-wake behavior: an uncontrolled trial

    NARCIS (Netherlands)

    Koch, B.C.P.; Hagen, E.C.; Nagtegaal, J.E.; Boringa, J.B.S.; Kerkhof, G.A.; ter Wee, P.M.

    2009-01-01

    Background: End-stage renal disease and its treatment are associated with sleep disturbances such as deterioration of the circadian sleep-wake pattern. Melatonin rhythm, which has an important role in this pattern, is disturbed. The nocturnal melatonin surge is absent in this population. Whether

  14. Vorticity generation and wake transition for a translating circular cylinder: Wall proximity and rotation effects

    DEFF Research Database (Denmark)

    Hourigan, K.; Rao, A.; Brøns, Morten

    2013-01-01

    dramatically under the influence of cylinder rotation and wall proximity. At gaps between the cylinder and the wall of less than approximately 0.25 cylinder diameter, the wake becomes three dimensional prior to becoming unsteady, while for larger gaps the initial transition is to an unsteady two...

  15. Wake-promoting effects of ONO-4127Na, a prostaglandin DP1 receptor antagonist, in hypocretin/orexin deficient narcoleptic mice.

    Science.gov (United States)

    Sagawa, Yohei; Sato, Masatoshi; Sakai, Noriaki; Chikahisa, Sachiko; Chiba, Shintaro; Maruyama, Takashi; Yamamoto, Junki; Nishino, Seiji

    2016-11-01

    Prostaglandin (PG)D2 is an endogenous sleep substance, and a series of animal studies reported that PGD2 or PGD2 receptor (DP1) agonists promote sleep, while DP1 antagonists promote wakefulness. This suggests the possibility of use of PG DP1 antagonists as wake-promoting compounds. We therefore evaluated the wake-promoting effects of ONO-4127Na, a DP1 antagonist, in a mouse model of narcolepsy (i.e., orexin/ataxin-3 transgenic mice) and compared those to effects of modafinil. ONO-4127Na perfused in the basal forebrain (BF) area potently promoted wakefulness in both wild type and narcoleptic mice, and the wake-promoting effects of ONO-4127Na at 2.93 × 10(-4) M roughly corresponded to those of modafinil at 100 mg/kg (p.o.). The wake promoting effects of ONO-4127Na was observed both during light and dark periods, and much larger effects were seen during the light period when mice slept most of the time. ONO-4127Na, when perfused in the hypothalamic area, had no effects on sleep. We further demonstrated that wake-promoting effects of ONO-4127Na were abolished in DP1 KO mice, confirming that the wake-promoting effect of ONO-4127Na is mediated by blockade of the PG DP1 receptors located in the BF area. ONO-4127Na reduced DREM, an EEG/EMG assessment of behavioral cataplexy in narcoleptic mice, suggesting that ONO-4127Na is likely to have anticataplectic effects. DP1 antagonists may be a new class of compounds for the treatment of narcolepsy-cataplexy, and further studies are warranted. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. Wind effects on long-span bridges: Probabilistic wind data format for buffeting and VIV load assessments

    Science.gov (United States)

    Hoffmann, K.; Srouji, R. G.; Hansen, S. O.

    2017-12-01

    The technology development within the structural design of long-span bridges in Norwegian fjords has created a need for reformulating the calculation format and the physical quantities used to describe the properties of wind and the associated wind-induced effects on bridge decks. Parts of a new probabilistic format describing the incoming, undisturbed wind is presented. It is expected that a fixed probabilistic format will facilitate a more physically consistent and precise description of the wind conditions, which in turn increase the accuracy and considerably reduce uncertainties in wind load assessments. Because the format is probabilistic, a quantification of the level of safety and uncertainty in predicted wind loads is readily accessible. A simple buffeting response calculation demonstrates the use of probabilistic wind data in the assessment of wind loads and responses. Furthermore, vortex-induced fatigue damage is discussed in relation to probabilistic wind turbulence data and response measurements from wind tunnel tests.

  17. The MISSE 7 Flexural Stress Effects Experiment After 1.5 Years of Wake Space Exposure

    Science.gov (United States)

    Snow, Kate E.; De Groh, Kim K.; Banks, Bruce A.

    2017-01-01

    Low Earth orbit space environment conditions, including ultraviolet radiation, thermal cycling, and atomic oxygen exposure, can cause degradation of exterior spacecraft materials over time. Radiation and thermal exposure often results in bond- breaking and embrittlement of polymers, reducing mechanical strength and structural integrity. An experiment called the Flexural Stress Effects Experiment (FSEE) was flown with the objective of determining the role of space environmental exposure on the degradation of polymers under flexural stress. The FSEE samples were flown in the wake orientation on the exterior of International Space Station for 1.5 years. Twenty-four samples were flown: 12 bent over a 0.375 in. mandrel and 12 were over a 0.25 in. mandrel. This was designed to simulate flight configurations of insulation blankets on spacecraft. The samples consisted of assorted polyimide and fluorinated polymers with various coatings. Half the samples were designated for bend testing and the other half will be tensile tested. A non-standard bend-test procedure was designed to determine the surface strain at which embrittled polymers crack. All ten samples designated for bend testing have been tested. None of the control samples' polymers cracked, even under surface strains up to 19.7%, although one coating cracked. Of the ten flight samples tested, seven show increased embrittlement through bend-test induced cracking at surface strains from 0.70%to 11.73%. These results show that most of the tested polymers are embrittled due to space exposure, when compared to their control samples. Determination of the extent of space induced embrittlement of polymers is important for designing durable spacecraft.

  18. The Effects of Kangaroo Care on the Sleep and Wake States of Preterm Infants.

    Science.gov (United States)

    Bastani, Farideh; Rajai, Nahid; Farsi, Zahra; Als, Heidelise

    2017-06-01

    Developing interventions that improve deep sleep and quit awake is important to improve the quality of care that is provided to preterm infants. The aim of this study was to compare the effects of kangaroo care and in-arms-holding on the sleep and wake states of preterm infants. A randomized controlled trial design was employed in 2011-2012. Seventy-two stable preterm infants with gestational ages of 32-37 weeks and their mothers were recruited from the neonatal intensive care unit of Valiasr Hospital in Tehran, Iran. Seventy participants completed the trial. In the preintervention phase, nurses placed all of the infants, clad only in diapers, in supine position in their incubator for 20 minutes. Next, the infants in the kangaroo care group were placed onto their mothers' bare chest, whereas those infants in the in-arms-holding group were cradled in their mothers' arms, with the head and back supported by the mother's left arm. The intervention period lasted for 70 minutes. In the postintervention phase, the infants were returned to their incubators and placed in supine position for 20 minutes. The observer recorded the status of the infants during the three phases of study. There were no significant differences between the two groups in terms of state distribution in the preintervention phase. However, the kangaroo care group had longer periods in deep sleep (p preterm infants spend in deep sleep and quiet awake states as compared with simply being held in their mothers' arms. Replication of this research will strengthen the results.

  19. The effect of vegetation on wind-blown mass transport at the regional scale: A wind tunnel experiment

    NARCIS (Netherlands)

    Youssef, I.F.; Visser, S.M.; Karssenberg, D.; Erpul, G.; Cornelis, W.M.; Gabriels, D.; Poortinga, A.

    2012-01-01

    Wind erosion is a global environmental problem. Re-vegetating land is a commonly used method to reduce the negative effects of wind erosion. However, there is limited knowledge on the effect of vegetation pattern on wind-blown mass transport. The objective of this study was to investigate the effect

  20. Droop assignment algorithm for the inertial control of a DFIG-based wind power plant for supporting the grid frequency

    DEFF Research Database (Denmark)

    Lee, Jinsik; Kang, Yong Cheol; Muljadi, Edward

    2014-01-01

    In a wind power plant (WPP) consisting of multiple wind generators (WGs), the wind speed of WGs at the downstream side decreases due to the wake effect, and thus their rotor speeds are smaller than those of the upstream WGs because of an MPPT operation. Therefore, WGs in a WPP have different amou...

  1. An experimental investigation into the effect of Marine Hydrokinetic (MHK) turbine array spacing on turbine efficiency and turbine wake characteristics

    Science.gov (United States)

    Stelzenmuller, Nick; Aliseda, Alberto

    2012-11-01

    Three 1/45 MHK turbine scale models were tested in a flume at various array spacings. The model turbines were instrumented to measure torque and angular velocity. Incident flow on the turbines and in the wakes was characterized via PIV and ADV measurements. Flow characteristics: mean velocity, turbulence intensity, and vorticity are correlated with turbine performance. Tip speed ratio (TSR) similarity (although not Reynolds number) of the turbines is achieved by controlling the applied load with magnetic brakes inside the model turbine nacelles. Wake characteristics and turbine efficiencies were investigated at a range of TSRs, with the goal of ``tuning'' an array to maximize overall array efficiency. Grids were placed in the flume upstream of the turbine array in order to change the turbulence intensity of the flow incident to the array. High levels of turbulence intensity in the incident flow is consistent with natural conditions in tidal currents, and has a strong effect on turbine wake dissipation. These experiments used a ``reference model'' turbine geometry developed for DOE at the National Renewable Energy Laboratory for the purpose of facilitating the comparison of experimental and numerical results in marine hydrokinetic turbine research.

  2. Results from operation and research of the experimental wind farm of the Dutch electricity generating board

    International Nuclear Information System (INIS)

    Toussaint, P.; Hutting, H.K.; Mortier, M.; Cleijne, J.W.

    1992-01-01

    This combined paper consists of four parts. The order of the above authors corresponds to the order of the parts. The first part deals with the operational experience of the farm. It reports an average capacity factor of 24% and an availability of 90%. The second part reports measured power losses due to wake effects, while the third part shows wind velocity deficits and turbulence characteristics within a wake. In the last part the application of a wind farm controller is demonstrated. (au)

  3. Solar Wind MHD Turbulence: Anomalous Scaling and Intermittency Effects in the Slow and Fast Wind

    Science.gov (United States)

    Salem, C.; Mangeney, A.; Bale, S. D.

    2007-12-01

    Although considerable progress has been made in the understanding of MHD turbulence over the past few decades through the analysis of in-situ solar wind data, two of the primary problems of solar wind MHD turbulence that still remain a puzzle are the nature of the nonlinear energy cascade, and the strong intermittent character of solar wind fluctuations in the inertial range. This intermittency modifies significantly the scaling exponents of actual power-law spectra, which are directly related to the physical nature of the energy cascade taking place in the solar wind. The identification of the most intermittent structures and their relation to dissipation represents then a crucial problem in the framework of turbulence. Anomalous scaling of both solar wind magnetic field and velocity fluctuations in the inertial range, as well as intermittency effects have recently been investigated in detail using Wavelet transforms on simultaneous WIND 3s resolution particle and magnetic field data from the 3DP and the MFi experiments respectively. Specifically, the Haar Wavelet transform is used to compute spectra, structure functions and probability distribution functions (PDFs). This powerful technique allows: (1) for a systematic study of intermittency effects on these spectra, structure functions and PDFs, thus for a clear determination of the actual scaling properties in the inertial range, and (2) for a direct and systematic identification of the most active, singular structures responsible for the intermittency in the solar wind. The analysis of structure functions and PDFs, as well as new results on the nature of the intermittent coherent structures will be presented. The turbulent properties and intermittency effects in different solar wind regimes will be also discussed.

  4. Wind Effects on Retention Time in Highway Ponds

    DEFF Research Database (Denmark)

    Bentzen, Thomas Ruby; Larsen, Torben; Rasmussen, Michael R.

    2007-01-01

    is to evaluate the quality of long term simulations based on historical rain series of the pollutant discharges from roads and highways. The idea of this paper is to evaluate the effects of wind on the retention time and compare the retention time for the situation of a spatial uniform wind shear stress...

  5. Wind Effects on Retention Time in Highway Ponds

    DEFF Research Database (Denmark)

    Bentzen, Thomas Ruby; Larsen, Torben; Rasmussen, Michael R.

    2008-01-01

    is to evaluate the quality of long term simulations based on historical rain series of the pollutant discharges from roads and highways. The idea of this paper is to evaluate the effects of wind on the retention time and compare the retention time for the situation of a spatial uniform wind shear stress...

  6. Effects of offshore wind farms on birds

    DEFF Research Database (Denmark)

    Petersen, Ib Krag; Fox, Anthony David; Desholm, Mark

    På konferencen "Offshore Wind Energy Development Site Assessment and Characterization: Evaluation of the Current Status and European Experience" blev der gjort rede for danske erfaringer med effekten af havvindmølleparker på havfugle.......På konferencen "Offshore Wind Energy Development Site Assessment and Characterization: Evaluation of the Current Status and European Experience" blev der gjort rede for danske erfaringer med effekten af havvindmølleparker på havfugle....

  7. The effect of vegetation patterns on wind-blown mass transport at the regional scale: A wind tunnel experiment

    NARCIS (Netherlands)

    Youssef, F.; Visser, S.; Karssenberg, D.J.; Erpul, G.; Cornelis, W.M.; Gabriels, D.; Poortinga, A.

    2012-01-01

    Abstract Wind erosion is a global environmental problem. Re-vegetating land is a commonly used method to reduce the negative effects of wind erosion. However, there is limited knowledge on the effect of vegetation pattern on wind-blown mass transport. The objective of this study was to investigate

  8. Accommodating adolescent sleep-wake patterns: the effects of shifting the timing of sleep on training effectiveness.

    Science.gov (United States)

    Miller, Nita Lewis; Tvaryanas, Anthony P; Shattuck, Lawrence G

    2012-08-01

    This study evaluated the effect of accommodating adolescent sleep-wake patterns by altering the timing of the major sleep period of US Army recruits. The quasi-experimental study compared recruits assigned to one of two training companies: one with a customary sleep regimen (20:30 to 04:30) while the other employed a phase-delayed sleep regimen (23:00 to 07:00), the latter aligning better with biologically driven sleep-wake patterns of adolescents. The study was conducted during Basic Combat Training (BCT) at Fort Leonard Wood, Missouri. TRAINEES: The study included 392 trainees: 209 received the intervention, while 183 composed the Comparison group. Demographic and psychophysiological measures were collected on all trainees. Weekly assessments of subjective fatigue and mood, periodic physical fitness, marksmanship scores, and attrition rates from BCT were studied. Actigraphy was collected on approximately 24% of trainees. Based on actigraphy, trainees on the phase-delayed sleep schedule obtained 31 m more sleep/night than trainees on the customary sleep schedule. The Intervention group reported less total mood disturbance relative to baseline. Improvements in marksmanship correlated positively with average nightly sleep during the preceding week when basic marksmanship skills were taught. No differences were seen in physical fitness or attrition rates. In contrast to the Intervention group, the Comparison group was 2.3 times more likely to experience occupationally significant fatigue and 5.5 times more likely to report poor sleep quality. Accommodating adolescent sleep patterns significantly improves mental health and performance in the training environment.

  9. Wind farm production estimates

    DEFF Research Database (Denmark)

    Larsen, Torben J.; Larsen, Gunner Chr.; Aagaard Madsen, Helge

    2012-01-01

    inves- tigated for a full polar (i.e. as function of mean inflow wind direction). This investigation relates to a mean wind speed bin defined as 8m=s±1m=s. The impact of ambient turbu- lence intensity and turbine inter spacing on the production of a wind turbine operating under full wake conditions...... is investi- gated. Four different turbine inter spacings, ranging between 3.8 and 10.4 rotor diameters, are analyzed for ambient turbu- lence intensities varying between 2% and 20%. This analysis is based on full scale production data from three other wind farms Wieringermeer [3], Horns Rev [4] and Nysted [5......]. A very satisfactory agreement between experimental data and predictions is observed. This paper finally includes additionally an analysis of the production impact caused by atmospheric stability effects. For this study, atmospheric stability conditions are defined in terms of the Monin-Obukhov length...

  10. Potential load reductions on megawatt turbines exposed to wakes using individual-pitch wake compensator and trailing-edge flaps

    DEFF Research Database (Denmark)

    Markou, Helen; Andersen, Peter Bjørn; Larsen, Gunner Chr.

    2011-01-01

    Wind turbines located in wind farms experience inflow wind conditions that are substantially modified compared with the ambient wind field that applies for stand-alone wind turbines because of upstream emitted wakes. This has implications not only for the power production of a wind farm, but also...... that typically focus on either load or power prediction. As a consequence, the wake affected inflow field generated by the DWM formulation opens for control strategies for the individual turbine. Two different control approaches for load reduction on the individual turbines are implemented in the multi-body aero-servo-elastic...... tool HAWC2, developed at Risø-DTU in Denmark, and their potential load reduction capabilities compared: (1) full-blade ‘individual-pitch controllers’ acting as wake compensators and (2) controllers using trailing-edge flaps. Information on the wake inflow conditions, induced by upstream turbines...

  11. Experimental and Numerical Investigation of the Effect of Rotor Blockage on Wake Expansion

    NARCIS (Netherlands)

    Akay, B.; Simao Ferreira, C.J.; Van Bussel, G.J.W.; Tescione, G.

    2010-01-01

    A detailed quantitative description of the aerodynamics of a horizontal axis wind turbine (HAWT) is difficult due to complexity of the flow field. Several methods from experimental to analytical are used to investigate the aerodynamics of a HAWT. In the present study, a wind tunnel experiment and

  12. Impact of a wind turbine on turbulence: Un-freezing turbulence by means of a simple vortex particle approach

    DEFF Research Database (Denmark)

    Branlard, Emmanuel Simon Pierre; Mercier, P.; Machefaux, Ewan

    2016-01-01

    the insertion point. The presence of the wind turbine and its wake is found to have insignificant effect on upstream turbulence. Finally, the mean velocity profiles in the wake are found to be in good agreement with both lidar measurements and CFD simulations. (C) 2016 Elsevier Ltd. All rights reserved....

  13. Comparison of the near-wake between actuator-line simulations and a simplified vortex model of a horizontal-axis wind turbine

    DEFF Research Database (Denmark)

    Sarmast, Sasan; Segalini, Antonio; Mikkelsen, Robert Flemming

    2016-01-01

    The flow around an isolated horizontal-axis wind turbine is estimated by means of a new vortex code based on the Biot–Savart law with constant circulation along the blades. The results have been compared with numerical simulations where the wind turbine blades are replaced with actuator lines. Two...... good, validating the analytical method for more general conditions. The present results show that a simple vortex code is able to provide an estimation of the flow around the wind turbine similar to the actuator-line approach but with a negligible computational effort. Copyright © 2015 John Wiley...

  14. A HPC “Cyber Wind Facility” Incorporating Fully-Coupled CFD/CSD for Turbine-Platform-Wake Interactions with the Atmosphere and Ocean

    Energy Technology Data Exchange (ETDEWEB)

    Brasseur, James G. [Univ. of Colorado, Boulder, CO (United States)

    2017-05-09

    The central aims of the DOE-supported “Cyber Wind Facility” project center on the recognition that wind turbines over land and ocean generate power from atmospheric winds that are inherently turbulent and strongly varying, both spatially over the rotor disk and in temporally as the rotating blades pass through atmospheric eddies embedded within the mean wind. The daytime unstable atmospheric boundary layer (ABL) is particularly variable in space time as solar heating generates buoyancy-driven motions that interact with strong mean shear in the ABL “surface layer,” the lowest 200 - 300 m where wind turbines reside in farms. With the “Cyber Wind Facility” (CWF) program we initiate a research and technology direction in which “cyber data” are generated from “computational experiments” within a “facility” akin to a wind tunnel, but with true space-time atmospheric turbulence that drive utility-scale wind turbines at full-scale Reynolds numbers. With DOE support we generated the key “modules” within a computational framework to create a first generation Cyber Wind Facility (CWF) for single wind turbines in the daytime ABL---both over land where the ABL globally unstable and over water with closer-to-neutral atmospheric conditions but with time response strongly affected by wave-induced forcing of the wind turbine platform (here a buoy configuration). The CWF program has significantly improved the accuracy of actuator line models, evaluated with the Cyber Wind Facility in full blade-boundary-layer-resolved mode. The application of the CWF made in this program showed the existence of important ramp-like response events that likely contribute to bearing fatigue failure on the main shaft and that the advanced ALM method developed here captures the primary nonsteady response characteristics. Long-time analysis uncovered distinctive key dynamics that explain primary mechanisms that underlie potentially deleterious load transients. We also showed

  15. Size Effect on the Mechanical Properties of CF Winding Composite

    Science.gov (United States)

    Cui, Yuqing; Yin, Zhongwei

    2017-12-01

    Mechanical properties of filament winding composites are usually tested by NOL ring samples. Few people have studied the size effect of winding composite samples on the testing result of mechanical property. In this research, winding composite thickness, diameter, and geometry of NOL ring samples were prepared to investigate the size effect on the mechanical strength of carbon fiber (CF) winding composite. The CF T700, T1000, M40, and M50 were adopted for the winding composite, while the matrix was epoxy resin. Test results show that the tensile strength and ILSS of composites decreases monotonically with an increase of thickness from 1 mm to 4 mm. The mechanical strength of composite samples increases monotonically with the increase in diameter from 100 mm to 189 mm. The mechanical strength of composite samples with two flat sides are higher than those of cyclic annular samples.

  16. Wind tunnel study of a vertical axis wind turbine in a turbulent boundary layer flow

    Science.gov (United States)

    Rolin, Vincent; Porté-Agel, Fernando

    2015-04-01

    Vertical axis wind turbines (VAWTs) are in a relatively infant state of development when compared to their cousins the horizontal axis wind turbines. Very few studies have been carried out to characterize the wake flow behind VAWTs, and virtually none to observe the influence of the atmospheric boundary layer. Here we present results from an experiment carried out at the EPFL-WIRE boundary-layer wind tunnel and designed to study the interaction between a turbulent boundary layer flow and a VAWT. Specifically we use stereoscopic particle image velocimetry to observe and quantify the influence of the boundary layer flow on the wake generated by a VAWT, as well as the effect the VAWT has on the boundary layer flow profile downstream. We find that the wake behind the VAWT is strongly asymmetric, due to the varying aerodynamic forces on the blades as they change their position around the rotor. We also find that the wake adds strong turbulence levels to the flow, particularly on the periphery of the wake where vortices and strong velocity gradients are present. The boundary layer is also shown to cause greater momentum to be entrained downwards rather than upwards into the wake.

  17. Experimental investigation of main rotor wake

    Directory of Open Access Journals (Sweden)

    Stepanov Robert

    2017-01-01

    Full Text Available In this work, experimental results of rotor wake in hover mode are presented. The experiments were carried out with a rotor rig model in the T-1K wind tunnel in Kazan National Research Technical University (Kazan Aviation Institute. The rotor consisted of four identical blades. The Q-criterion was used to identify tip vortices for a 2D case. The results were then compared with two different wake models.

  18. Experimental investigation of main rotor wake

    OpenAIRE

    Stepanov Robert; Mikhailov Sergey

    2017-01-01

    In this work, experimental results of rotor wake in hover mode are presented. The experiments were carried out with a rotor rig model in the T-1K wind tunnel in Kazan National Research Technical University (Kazan Aviation Institute). The rotor consisted of four identical blades. The Q-criterion was used to identify tip vortices for a 2D case. The results were then compared with two different wake models.

  19. Wake fields and wake field acceleration

    International Nuclear Information System (INIS)

    Bane, K.L.F.; Wilson, P.B.; Weiland, T.

    1984-12-01

    In this lecture we introduce the concepts of wake fields and wake potentials, examine some basic properties of these functions, show how they can be calculated, and look briefly at a few important applications. One such application is wake field acceleration. The wake field accelerator is capable of producing the high gradients required for future very high energy e + e - linear colliders. The principles of wake field acceleration, and a brief description of experiments in progress in this area, are presented in the concluding section. 40 references, 27 figures

  20. Effects of wind turbines on human health and environment

    Energy Technology Data Exchange (ETDEWEB)

    Ramanan, G. [RV College of Engineering, Bangalore (India); Pandian, A.; Gowda, G.; Raghunandan, A. [MS RAMAIAH Institute of Technology, Bangalore (India)

    2012-07-01

    The impact of climate change through global warming has been a concern for some time now. Targets are being set for ratifying countries to reduce their CO{sup 2} emissions. In order to achieve reduction in CO{sup 2} emissions, there must be sustained move in the production of electricity from renewable sources other than fossil fuel combustion. Of the renewable energy sources, the most realistic and economic is Wind Power. The Asian continent is developing into one of the main powerhouses of Wind Energy. The strongest market leader in Wind Energy in the continent is India. On the flip side, there are some effects of Wind Turbines which are hazardous to human health like noise generated. Such hazards are also likely and known to affect the migratory birds during transition. This paper will address the effects of Wind Turbine on Human Health and Environment. The paper will focus on the following questions: (1)What are the potential health and environmental impacts of Wind Turbines? (2)How is exposure to Wind Turbine Noise assessed? (3)What consultation process with the community is required before Wind Farms are constructed? (Author)

  1. Wind-farm simulation over moderately complex terrain

    Science.gov (United States)

    Segalini, Antonio; Castellani, Francesco

    2017-05-01

    A comparison between three independent software to estimate the power production and the flow field in a wind farm is conducted, validating them against SCADA (Supervisory, Control And Data Acquisition) data. The three software were ORFEUS, WindSim and WAsP: ORFEUS and WAsP are linearised solvers, while WindSim is fully nonlinear. A wake model (namely a prescribed velocity deficit associated to the turbines) is used by WAsP, while ORFEUS and WindSim use the actuator-disc method to account for the turbines presence. The comparison indicates that ORFEUS and WAsP perform slightly better than WindSim in the assessment of the polar efficiency. The wakes simulated with ORFEUS appear more persistent than the ones of WindSim, which uses a two-equation closure model for the turbulence effects.

  2. Wind turbine sound and health effects : an expert panel review

    International Nuclear Information System (INIS)

    Colby, D.; Lipscomb, D.M.; McCunney, R.J.; Seilo, M.T.; Sondergaard, B.

    2009-12-01

    This paper presented the results of a study conducted to review the current literature available on the perceived health effects of wind turbines. The review was conducted by a multidisciplinary panel comprised of audiologists, medical doctors, and acoustical professionals from throughout the world. The document was prepared as a reference point for legislators, regulators and other stakeholders in need of information about wind turbine sounds. A large body of peer-reviewed literature on sound and health effects in general were reviewed in order to assess the plausible biological effects of exposure to wind turbine sound. A review of potential environmental exposures associated with wind turbine operations was conducted. Results of the study indicated that there is no evidence that the sounds emitted by wind turbines have any direct adverse physiological effects, and that the ground-borne vibrations from wind turbines are too weak to be detected or to affect humans. The panel concluded that the sounds from wind turbines can not plausibly have direct adverse health consequences. 126 refs., 3 tabs., 4 figs., 5 appendices.

  3. Hydrodynamic effects of nuclear active galaxy winds on host galaxies

    International Nuclear Information System (INIS)

    Schiano, A.V.R.

    1984-01-01

    In order to test the hypothesized existence of a powerful, thermal wind in active galactic nuclei, the hydrodynamic effects of such a wind on a model galactic interstellar medium (ISM) are investigated. The properties of several model ISMs are derived from observations of the Milky Way's ISM and those of nearby spiral and elliptical galaxies. The propagation of the wind into the low density gas component of the ISM is studied using the Kompaneets approximation of a strong explosion in an exponential atmosphere. Flattened gas distributions are shown to experience blow-out of wind gas along the symmetry axis. Next, the interaction of dense, interstellar clouds with the wind is investigated. The stability and mass loss of clouds in the wind are studied and it is proposed that clouds survive the encounter with the wind over large timescales. It is proposed that the narrow emission line regions (NELR) of active galaxies are the result of the interaction of active nuclei photons and a thermal wind on large, interstellar clouds

  4. Effects of the Horns Reef wind farm on harbour porpoises

    International Nuclear Information System (INIS)

    Tougaard, J.; Teilmann, J.; Rye Hansen, J.

    2004-09-01

    Horns Reef offshore wind farm was established in 2002. It consists of 80 2 MW wind turbines, mounted on steel monopile foundations. A harbour porpoise monitoring program was set up in connection with the environmental impact assessment (EIA) of the wind farm project. This monitoring program started in 1999 with collection of baseline data and has continued though construction and operational period. The program continues through 2005. Baseline studies showed that harbour porpoises are abundant in the area, including the area where the wind farm is now located. Significant effects on behaviour and distribution of the porpoises were observed during the construction of the wind farm. Changes could be linked to pile driving operations, where monopile foundations were rammed into the seabed. This procedure produced high levels of underwater noise and mitigation procedures in the form of a ramp up procedure and deployment of acoustic alarms were employed. During the construction period very few animals were observed inside the wind farm area. Acoustic monitoring data showed a significant increase in waiting time between porpoise encounters in connection with pile driving operations, followed by a rapid return to levels normal for the construction period as a whole. However, when the entire construction period was considered as a whole, T-POD activity increased relative to baseline. Observations during operation of the wind farm in 2003 showed a return to baseline levels on most of the indicators derived from the acoustic monitoring and animals were again seen inside the wind farm area. (au)

  5. Soil tillage and windbreak effects on millet and cowpea: I. Wind speed, evaporation, and wind erosion

    Energy Technology Data Exchange (ETDEWEB)

    Banzhaf, J.; Leihner, D.E.; Buerkert, A. (Univ. of Hohenheim, Stuttgart (Germany)); Serafini, P.G. (Univ. of Arkansas, Fayetteville (United States))

    Deforestation, overgrazing, and declining soil regeneration periods have resulted in increased wind erosion problems in dry areas of the West African Sahel, but little is known about the bio-physical factors involved. This research was conducted to determine the effects of ridging and four different windbreak spacings on wind erosion, potential evaporation, and soil water reserves. A field trial was conducted from 1985 to 1987 on 12 ha of a Psammentic Paleustalf in Southern Niger. Millet, Pennisetum glaucum (L.), and cowpea, Vigna unguiculata (L.) Walp., were seeded in strips on flat and ridged soil. Windbreaks of savannah vegetation were spaced at 6, 20, 40, and 90 m. The effects of ridging on wind speed, evaporation, and wind erosion were small and mostly non-significant. However, average wind speed at 0.3 m above ground in the center of cowpea and millet strips was significantly reduced from 2.8 to 2.1 m s[sup [minus]1] as windbreak distances narrowed from 90 to 6 m. As a consequence, potential evaporation declined by 15% and the amount of windblown soil particles by 50% in ridged and by 70% in flat treatments. Despite reduced potential evaporation, average subsoil water reserves were 14 mm smaller in the 6- than in the 20-m windbreak spacing indicating excessive water extraction by the windbreak vegetation. Thus, establishing windbreaks with natural savannah vegetation may require a careful consideration of the agronomic benefits and costs to competing crops. 21 refs., 5 figs.

  6. Soil tillage and windbreak effects on millet and cowpea: I. Wind speed, evaporation, and wind erosion

    International Nuclear Information System (INIS)

    Banzhaf, J.; Leihner, D.E.; Buerkert, A.; Serafini, P.G.

    1992-01-01

    Deforestation, overgrazing, and declining soil regeneration periods have resulted in increased wind erosion problems in dry areas of the West African Sahel, but little is known about the bio-physical factors involved. This research was conducted to determine the effects of ridging and four different windbreak spacings on wind erosion, potential evaporation, and soil water reserves. A field trial was conducted from 1985 to 1987 on 12 ha of a Psammentic Paleustalf in Southern Niger. Millet, Pennisetum glaucum (L.), and cowpea, Vigna unguiculata (L.) Walp., were seeded in strips on flat and ridged soil. Windbreaks of savannah vegetation were spaced at 6, 20, 40, and 90 m. The effects of ridging on wind speed, evaporation, and wind erosion were small and mostly non-significant. However, average wind speed at 0.3 m above ground in the center of cowpea and millet strips was significantly reduced from 2.8 to 2.1 m s -1 as windbreak distances narrowed from 90 to 6 m. As a consequence, potential evaporation declined by 15% and the amount of windblown soil particles by 50% in ridged and by 70% in flat treatments. Despite reduced potential evaporation, average subsoil water reserves were 14 mm smaller in the 6- than in the 20-m windbreak spacing indicating excessive water extraction by the windbreak vegetation. Thus, establishing windbreaks with natural savannah vegetation may require a careful consideration of the agronomic benefits and costs to competing crops. 21 refs., 5 figs

  7. Dispersion in the wake of a model industrial complex

    International Nuclear Information System (INIS)

    Hatcher, R.V.; Meroney, R.N.; Peterka, J.A.; Kothari, K.

    1977-06-01

    Models (1:200 scale) of the EOCR reactor building and surrounding silo and tank buildings at the Idaho National Engineering Laboratory, Idaho Falls, Idaho were put into the Meteorological Wind Tunnel at Colorado State University for the purpose of studying the effects of building wakes on dispersion. Flow visualization was done and concentration measurements were taken. The test program consisted of systematic releases from ground, building height, and stack height sources with no appreciable plume rise. The program was repeated for cases of moderately unstable, neutral, moderately stable, and stable conditions in the wind tunnel. Results show that the buildings significantly alter the dispersion patterns and the addition of any extra buildings or slight terrain change in the immediate vicinity of the building has a major effect. In the near wake region the effects of stratification were still evident causing slightly higher concentrations for stable conditions and slightly lower for unstable. Current dispersion models are discussed and evaluated that predict concentrations in the building wake region

  8. Framework of Multi-objective Wind Farm Controller Applicable to Real Wind Farms

    DEFF Research Database (Denmark)

    Kazda, Jonas; Gögmen, Tuhfe; Giebel, Gregor

    2016-01-01

    Optimal wind farm control can mitigate adverse wake effects that can potentially cause up to 40% power loss and 80% increased fatigue loads in wind farms. The aim of this work is to outline a methodological framework of an optimal wind farm controller, which provides improved solutions to critical...... areas of optimal wind farm control research. The basis of this framework is a review of optimal wind farm control methodologies, which is presented first. It is observed that there is, at present, mainly a need for more advanced wind farm operation models. Thereafter the framework of a multi...... in the wind farm. The controller design provides improved solutions for the modelling of wind farm aerodynamics and turbine operation, that is the PossPOW algorithm and a HAWC2-based turbine model, respectively. Moreover, all components of the framework are designed as to enable the applicability...

  9. Fast wake measurements with LiDAR at Risø test field

    DEFF Research Database (Denmark)

    Bingöl, Ferhat; Trujillo, J.J.; Mann, Jakob

    2008-01-01

    The vast majority of wind turbines are today erected in wind farms. As a consequence, wake generated loads are becoming more and more important. We present a new and successful experimental technique, based on remote sensing, to measure instantaneously the flow in the wake of wind turbines. Downs...

  10. Acute Total and Chronic Partial Sleep Deprivation: Effects on Neurobehavioral Functions, Waking EEG and Renin-Angiotensin System

    Science.gov (United States)

    Dijk, Derk-Jan

    1999-01-01

    Total sleep deprivation leads to decrements in neurobehavioral performance and changes in electroencephalographic (EEG) oscillations as well as the incidence of slow eye movements ad detected in the electro-oculogram (EOG) during wakefulness. Although total sleep deprivation is a powerful tool to investigate the association of EEG/EOG and neurobehavioral decrements, sleep loss during space flight is usual only partial. Furthermore exposure to the microgravity environment leads to changes in sodium and volume homeostasis and associated renal and cardio-endocrine responses. Some of these changes can be induced in head down tilt bedrest studies. We integrate research tools and research projects to enhance the fidelity of the simulated conditions of space flight which are characterized by complexity and mutual interactions. The effectiveness of countermeasures and physiologic mechanisms underlying neurobehavioral changes and renal-cardio endocrine changes are investigated in Project 3 of the Human Performance Team and Project 3 of the Cardiovascular Alterations Team respectively. Although the. specific aims of these two projects are very different, they employ very similar research protocols. Thus, both projects investigate the effects of posture/bedrest and sleep deprivation (total or partial) on outcome measures relevant to their specific aims. The main aim of this enhancement grant is to exploit the similarities in research protocols by including the assessment of outcome variables relevant to the Renal-Cardio project in the research protocol of Project 3 of the Human Performance Team and by including the assessment of outcome variables relevant to the Quantitative EEG and Sleep Deprivation Project in the research protocols of Project 3 of the Cardiovascular Alterations team. In particular we will assess Neurobehavioral Function and Waking EEG in the research protocols of the renal-cardio endocrine project and renin-angiotensin and cardiac function in the research

  11. Turbulent inflow and wake of a marine hydrokinetic turbine, including effects of wave motion

    Science.gov (United States)

    Dewhurst, Toby; Rowell, Matthew; Decew, Judson; Baldwin, Ken; Swift, Rob; Wosnik, Martin

    2012-11-01

    A research program to investigate the spatio-temporal structure of turbulent flows relevant to marine hydrokinetic (MHK) energy conversion, including turbulent inflow and turbine wakes, has been initiated at UNH. A scale model MHK turbine was deployed from a floating platform at two open water tidal energy test sites, one sheltered (Great Bay Estuary, NH) and one exposed (Muskeget Channel, MA). The inflow upstream of the turbine under test was characterized using an acoustic Doppler Velocimeter (ADV) and an acoustic Doppler current profiler (ADCP), which vary considerably in temporal and spatial resolution as well as practical applicability in this environment. The turbine was operated at previously determined peak efficiency for a given tidal current. The wake of the turbine was measured with a second, traversing ADV during ramp-up and at peak tidal current velocities, at two to six shroud diameters downstream. An inertial motion unit installed near the turbine hub is used to correct for platform motion. A platform-mounted wave-staff and an independently taut-moored pressure sensor were used to measure wave climate. Together, these data are used to validate theoretical and tank model results for utilizing surface-based platforms for MHK turbine deployments.

  12. Role of noradrenaline in wake promotion effect of orexin-A on alcohol coma in rats

    Directory of Open Access Journals (Sweden)

    Tian-hao WANG

    2013-02-01

    Full Text Available Objective  To study whether or not noradrenaline system participates in the process of orexin-A wake-promoting from alcohol coma. Methods  Twenty-four adult female SPF SD rats were divided into four groups, 6 each, and the model of alcohol coma was reproduced. Experimental rats were then divided randomly into rats receiving injection of artificial cerebrospinal fluid (ACSF, control group, orexin-A (orexin-A group, noradrenaline α1 receptor antagonists--prazosin (prazosin group, or prazosin + orexin-A (prazosin-orexin-A group into the lateral ventricle. The depth of coma was evaluated by the duration of loss of righting reflex (LORR and δ wave in electrocorticogram (ECoG. Results  The duration of LORR was significantly longer and the ratio of δ wave higher in the prazosin-treated rats than those in control group (P0.05. But the values were significantly different from those in the orexin-A group (P<0.01. Conclusion  Noradrenaline system may participate in the wake-promoting process of alcohol coma by orexin-A.

  13. The effect of wind power installations on coastal tourism

    Energy Technology Data Exchange (ETDEWEB)

    Blaydes Lilley, M.; Firestone, J.; Kempton, W. [Center for Carbon-free Power Integration, College of Earth, Ocean, and Environment, University of Delaware, Newark, DE 19716 (United States)

    2010-07-01

    We surveyed more than 1,000 randomly sampled, out-of-state tourists at Delaware, USA beaches in 2007. After providing respondents with wind turbine project photo-simulations at several distances, we inquired about the effect development would have on visitation. Approximately one-quarter stated that they would switch beaches if an offshore wind project was located 10 km from the coast, with avoidance diminishing with greater distance from shore. Stated avoidance is less than: avoidance with a fossil fuel power plant located the same distance inland; attraction to a beach with offshore wind turbines; and the percentage stating they would likely pay to take a boat tour. (author)

  14. The effect of wind power installations on coastal tourism

    International Nuclear Information System (INIS)

    Blaydes Lilley, M.; Firestone, J.; Kempton, W.

    2010-01-01

    We surveyed more than 1,000 randomly sampled, out-of-state tourists at Delaware, USA beaches in 2007. After providing respondents with wind turbine project photo-simulations at several distances, we inquired about the effect development would have on visitation. Approximately one-quarter stated that they would switch beaches if an offshore wind project was located 10 km from the coast, with avoidance diminishing with greater distance from shore. Stated avoidance is less than: avoidance with a fossil fuel power plant located the same distance inland; attraction to a beach with offshore wind turbines; and the percentage stating they would likely pay to take a boat tour. (author)

  15. Effects of Icing on Wind Turbine Fatigue Loads

    International Nuclear Information System (INIS)

    Frohboese, Peter; Anders, Andreas

    2007-01-01

    The external conditions occurring at cold climate sites will affect wind turbines in different ways. The effects of ice accretion on wind turbines and the influence on the turbine fatigue loads are examined. The amount of icing prior to turbine installation needs to be estimated by using standard measurement data and considering the geometry of the proposed turbine. A procedure to calculate the expected ice accretion on wind turbines out of standard measurement data is explained and the results are discussed. Different parameters to describe the accreted ice on the turbine are examined separately in a fatigue load calculation. The results of the fatigue load calculation are discussed and selected cases are presented

  16. The effect of nocturnal blue light exposure from light-emitting diodes on wakefulness and energy metabolism the following morning.

    Science.gov (United States)

    Kayaba, Momoko; Iwayama, Kaito; Ogata, Hitomi; Seya, Yumi; Kiyono, Ken; Satoh, Makoto; Tokuyama, Kumpei

    2014-09-01

    The control of sleep/wakefulness is associated with the regulation of energy metabolism. The present experiment was designed to assess the effect of nocturnal blue light exposure on the control of sleep/wakefulness and energy metabolism until next noon. In a balanced cross-over design, nine young male subjects sitting in a room-size metabolic chamber were exposed either to blue LEDs or to no light for 2 h in the evening. Wavelength of monochromatic LEDs was 465 nm and its intensity was 12.1 μW/cm(2). During sleep, sleep architecture and alpha and delta power of EEG were similar in the two experimental conditions. However, the following morning, when subjects were instructed to stay awake in a sitting position, duration judged as sleep at stages 1 and 2 was longer for subjects who received than for those who received no light exposure. Energy metabolism during sleep was not affected by evening blue light exposure, but the next morning energy expenditure, oxygen consumption, carbon dioxide production and the thermic effect of breakfast were significantly lower in subjects who received blue light exposure than in those who received no light exposure. Exposure to low intensity blue light in the evening, which does not affect sleep architecture and energy metabolism during sleep, elicits drowsiness and suppression of energy metabolism the following morning.

  17. Wind tunnel experiments on the effects of tillage ridge features on wind erosion horizontal fluxes

    Directory of Open Access Journals (Sweden)

    M. Kardous

    2005-11-01

    Full Text Available In addition to the well-known soil factors which control wind erosion on flat, unridged surfaces, two specific processes affect the susceptibility of tillage ridged surfaces to wind erosion: ridge-induced roughness and ridge- trapping efficiency. In order to parameterize horizontal soil fluxes produced by wind over tillage ridges, eight-ridge configurations composed of sandy soil and exhibiting ridge heights to ridge spacing (RH/RS ratios ranging from 0.18 to 0.38 were experimented in a wind tunnel. These experiments are used to develop a parameterization of the horizontal fluxes over tillage ridged surfaces based only on the geometric characteristics of the ridges. Indeed, the key parameters controlling the horizontal flux, namely the friction velocity, threshold friction velocity and the adjustment coefficient, are derived through specific expressions, from ridge heights (RH and ridge spacing (RS. This parameterization was evaluated by comparing the results of the simulations to an additional experimental data set and to the data set obtained by Hagen and Armbrust (1992. In both cases, predicted and measured values are found to be in a satisfying agreement. This parameterization was used to evaluate the efficiency of ridges in reducing wind erosion. The results show that ridged surfaces, when compared to a loose, unridged soil surface, lead to an important reduction in the horizontal fluxes (exceeding 60%. Moreover, the effect of ridges in trapping particles contributes for more than 90% in the flux reduction while the ridge roughness effect is weak and decreases when the wind velocity increases.

  18. Wind tunnel experiments on the effects of tillage ridge features on wind erosion horizontal fluxes

    Directory of Open Access Journals (Sweden)

    M. Kardous

    2005-11-01

    Full Text Available In addition to the well-known soil factors which control wind erosion on flat, unridged surfaces, two specific processes affect the susceptibility of tillage ridged surfaces to wind erosion: ridge-induced roughness and ridge- trapping efficiency.

    In order to parameterize horizontal soil fluxes produced by wind over tillage ridges, eight-ridge configurations composed of sandy soil and exhibiting ridge heights to ridge spacing (RH/RS ratios ranging from 0.18 to 0.38 were experimented in a wind tunnel. These experiments are used to develop a parameterization of the horizontal fluxes over tillage ridged surfaces based only on the geometric characteristics of the ridges. Indeed, the key parameters controlling the horizontal flux, namely the friction velocity, threshold friction velocity and the adjustment coefficient, are derived through specific expressions, from ridge heights (RH and ridge spacing (RS. This parameterization was evaluated by comparing the results of the simulations to an additional experimental data set and to the data set obtained by Hagen and Armbrust (1992. In both cases, predicted and measured values are found to be in a satisfying agreement.

    This parameterization was used to evaluate the efficiency of ridges in reducing wind erosion. The results show that ridged surfaces, when compared to a loose, unridged soil surface, lead to an important reduction in the horizontal fluxes (exceeding 60%. Moreover, the effect of ridges in trapping particles contributes for more than 90% in the flux reduction while the ridge roughness effect is weak and decreases when the wind velocity increases.

  19. [Testing results of telemechanic system controlling train operators wakefulness].

    Science.gov (United States)

    Serikov, V V; Zakrevskaia, A A; Zakharchenko, D V; Alpaev, D V; At'kova, E O

    2015-01-01

    Expert and instrumental assessment covered efficiency of telemechanic system controlling train operators wakefulness in simulation of real night travel, through special simulator complex "Locomotive operator cabin". The telemechanic system controlling train operators wakefulness, if exploited correctly, provides wakefulness of the train operators at the level sufficient for the effective work. That is supported by distribution of falling asleep cases in experiments with activated or deactivated telemechanic system controlling train operators wakefulness. The study proved efficiency of telemechanic system controlling train operators wakefulness.

  20. Market protocols in ERCOT and their effect on wind generation

    International Nuclear Information System (INIS)

    Sioshansi, Ramteen; Hurlbut, David

    2010-01-01

    Integrating wind generation into power systems and wholesale electricity markets presents unique challenges due to the characteristics of wind power, including its limited dispatchability, variability in generation, difficulty in forecasting resource availability, and the geographic location of wind resources. Texas has had to deal with many of these issues beginning in 2002 when it restructured its electricity industry and introduced aggressive renewable portfolio standards that helped spur major investments in wind generation. In this paper we discuss the issues that have arisen in designing market protocols that take account of these special characteristics of wind generation and survey the regulatory and market rules that have been developed in Texas. We discuss the perverse incentives some of the rules gave wind generators to overschedule generation in order to receive balancing energy payments, and steps that have been taken to mitigate those incentive effects. Finally, we discuss more recent steps taken by the market operator and regulators to ensure transmission capacity is available for new wind generators that are expected to come online in the future. (author)

  1. Effects of distributing wind energy generation over Europe

    Energy Technology Data Exchange (ETDEWEB)

    Giebel, G. [Risoe National Lab., Wind Energy and Atmospheric Physics Dept., Roskilde (Denmark)

    1999-03-01

    Using data from 60 meteorological stations distributed all over Europe in conjunction with the National Grid Model (NGM) from the Rutherford Appleton Laboratory, the effects of the large-scale distribution of wind energy generation are studied. In some regions of Europe, wind energy already covers a significant proportion of the electricity demand. But the intermittence of the wind resource is always a limiting factor when penetration levels are high. Studies for single countries have shown that distributing the generation over a large area reduces the variability of the output and hence makes wind energy more appealing to utilities, since the stability requirement of the network are easier to fulfil. The data are analysed in terms of absolute highs and lows, temporal and spatial correlations. To assess the financial benefits, the NGM is used to evaluate the match of electricity demand and generation as well as the possibel savings of fossil fuel in an electricity grid incorporating various capacities of wind energy generation. To assess the value of wind energy on a trans-national scale, the European plant mix is modelled, and the NGM is used to simulate the scheduling of these plants in the presence of different penetrations of wind energy. (au) EU-JOULE-3. 11 refs.

  2. The effect of positioning on preterm infants' sleep-wake states and stress behaviours during exposure to environmental stressors.

    Science.gov (United States)

    Peng, Niang-Huei; Chen, Li-Li; Li, Tsai-Chung; Smith, Marlaine; Chang, Yu-Shan; Huang, Li-Chi

    2014-12-01

    Previous studies separately examined the effects of positioning or environmental stressors on preterm infants' sleep and stress. Since positioning and environmental stressors occur simultaneously during infant hospitalization exploring these variables in the same study may offer new insights. A quasi-experimental study by one-group interrupted time-series design. In the current study, a total of 22 preterm infants were enrolled. Each infant was moved to either the supine or prone position for an hour at a time. Infants were videotaped and the sleep-wake states, stress behaviours and environmental conditions (light, noise and stimulation/handling) were recorded during the observation period. A total of 80 observations from 22 infants were accrued. In the supine position, preterm infants demonstrated more frequent waking states after adjusting for various environmental stressors (p position after adjusting for various environmental stressors (p position is a more favourable position for facilitating sleep and reducing stress for preterm infants exposed to varying environmental stressors. Preterm infants present different stress behaviours in response to varying types of environmental stimuli. © The Author(s) 2013.

  3. Coastal Ohio Wind Project

    Energy Technology Data Exchange (ETDEWEB)

    Gorsevski, Peter [Bowling Green State Univ., OH (United States); Afjeh, Abdollah [Univ. of Toledo, OH (United States); Jamali, Mohsin [Univ. of Toledo, OH (United States); Bingman, Verner [Bowling Green State Univ., OH (United States)

    2014-04-04

    The Coastal Ohio Wind Project intends to address problems that impede deployment of wind turbines in the coastal and offshore regions of Northern Ohio. The project evaluates different wind turbine designs and the potential impact of offshore turbines on migratory and resident birds by developing multidisciplinary research, which involves wildlife biology, electrical and mechanical engineering, and geospatial science. Firstly, the project conducts cost and performance studies of two- and three-blade wind turbines using a turbine design suited for the Great Lakes. The numerical studies comprised an analysis and evaluation of the annual energy production of two- and three-blade wind turbines to determine the levelized cost of energy. This task also involved wind tunnel studies of model wind turbines to quantify the wake flow field of upwind and downwind wind turbine-tower arrangements. The experimental work included a study of a scaled model of an offshore wind turbine platform in a water tunnel. The levelized cost of energy work consisted of the development and application of a cost model to predict the cost of energy produced by a wind turbine system placed offshore. The analysis found that a floating two-blade wind turbine presents the most cost effective alternative for the Great Lakes. The load effects studies showed that the two-blade wind turbine model experiences less torque under all IEC Standard design load cases considered. Other load effects did not show this trend and depending on the design load cases, the two-bladed wind turbine showed higher or lower load effects. The experimental studies of the wake were conducted using smoke flow visualization and hot wire anemometry. Flow visualization studies showed that in the downwind turbine configuration the wake flow was insensitive to the presence of the blade and was very similar to that of the tower alone. On the other hand, in the upwind turbine configuration, increasing the rotor blade angle of attack

  4. An Investigation of the Effects of Discrete Wing Tip Jets on Wake Vortex Roll Up.

    Science.gov (United States)

    1983-08-01

    and Operating Problems, National Aeronautics and Space Administration, NASA SP 270, Hampton, Virginia, May, 1971. 5. Smith, Harriet J. "A Flight Test...December, 1980, pp. 861-866. 39. Flechner, Stuart G., Peter F. Jacobs , and Richard T. Whitcomb. "A High Subsonic Speed Wind Tunnel Investigation Of

  5. Effect of Severity of Esophageal Acidification on Sleep vs Wake Periods in Infants Presenting with Brief Resolved Unexplained Events.

    Science.gov (United States)

    Sankaran, Janani; Qureshi, Aslam H; Woodley, Frederick; Splaingard, Mark; Jadcherla, Sudarshan R

    2016-12-01

    To describe the pattern of gastroesophageal reflux (GER) events in wake and sleep states with increasing acid reflux index (ARI) in neonates and to test the hypothesis that GER-related symptoms are frequent in ARI >7% in wake state. Infants underwent 24-hour pH-impedance studies with 6-hour concurrent video-polysomnography studies. Data were stratified based on the 24-hour ARI (% duration that esophageal pH is 7% (abnormal). GER frequency, clearance mechanisms, and symptoms were distinguished during wake state and sleep state. Total wake and sleep duration was similar (P ≥ .2) in all ARI groups. Acidic events were frequent with increasing ARI in wake state vs sleep state (P ≤ .03). The symptom index increased with increasing ARI (P ≤ .02) in both wake state and sleep state. Acid clearance time increased with increasing ARI in wake state (P ≤ .02). In ARI > 7% vs ARI ≤ 7%, frequency of acidic GER events was higher (P ≤ .02) in wake state and sleep state; proximal migration of acid (P = .03) and acid clearance time were higher in wake state (P = .0005) only. Symptom index was higher in ARI >7% vs ARI ≤ 7% in wake state (P 7%) is associated with increased reflux-associated symptoms in wake state. Sleep state appears to be protective regardless of ARI, likely because of greater chemosensory thresholds. Attention to posture and movements during wake state can be helpful. Scrutiny for non-GER etiologies should occur for infants presenting with life-threatening symptoms. Copyright © 2016 Elsevier Inc. All rights reserved.

  6. Effects of eszopiclone and zolpidem on sleep-wake behavior, anxiety-like behavior and contextual memory in rats

    Science.gov (United States)

    Huang, Max P.; Radadia, Kushan; Macone, Brian W.; Auerbach, Sanford H.; Datta, Subimal

    2010-01-01

    At present, eszopiclone and zolpidem are the most commonly prescribed drugs for treating insomnia. Despite the established relationship between sleep disturbance and anxiety, it remains unknown whether targeted treatment for insomnia may affect acute anxiety. Therefore, the objective of this study was to examine the effects of three different doses (1, 3, and 10 mg/kg) of eszopiclone and zolpidem on the states of sleep and wakefulness, levels of anxiety-like behavior, and long-term contextual memory in footshock-induced anxious rats. The results of this study demonstrated that the administration of eszopiclone and zolpidem both were equally effective in attenuating footshock stressor-induced suppression of slow-wave sleep (SWS). The administration of eszopiclone at 1 mg/kg or zolpidem at 1 and 3 mg/kg doses showed a tendency for attenuating stressor-induced suppression of REM sleep. However, the REM sleep attenuating effects of these drugs disappeared when they were administered at higher doses. The administration of eszopiclone at 3 and 10 mg/kg doses and zolpidem at all three doses reduced the power of electroencephalographic theta band frequencies during wakefulness. In addition, the administration of eszopiclone at 1 and 3 mg/kg doses suppressed stressor-induced anxiety-like behavior. The administration of zolpidem at 1, 3, or 10 mg/kg doses was not effective in attenuating stressor-induced anxiety-like behavior. Contextual memory after administration of eszopiclone at 1 mg/kg dose had no effects, but was reduced significantly with increased dosage. Contextual memory after administration of zolpidem, at all three doses, was severely disrupted. The results of this study suggest that eszopiclone at a low dose could be used effectively to control anxiety and anxiety-induced insomnia. PMID:20153782

  7. Combining economic and fluid dynamic models to determine the optimal spacing in very large wind farms

    NARCIS (Netherlands)

    Stevens, Richard J.A.M.; Hobbs, Benjamin F.; Ramos, Andrés; Meneveau, Charles

    2017-01-01

    Wind turbine spacing is an important design parameter for wind farms. Placing turbines too close together reduces their power extraction because of wake effects and increases maintenance costs because of unsteady loading. Conversely, placing them further apart increases land and cabling costs, as

  8. Stochastic Wake Modelling Based on POD Analysis

    Directory of Open Access Journals (Sweden)

    David Bastine

    2018-03-01

    Full Text Available In this work, large eddy simulation data is analysed to investigate a new stochastic modeling approach for the wake of a wind turbine. The data is generated by the large eddy simulation (LES model PALM combined with an actuator disk with rotation representing the turbine. After applying a proper orthogonal decomposition (POD, three different stochastic models for the weighting coefficients of the POD modes are deduced resulting in three different wake models. Their performance is investigated mainly on the basis of aeroelastic simulations of a wind turbine in the wake. Three different load cases and their statistical characteristics are compared for the original LES, truncated PODs and the stochastic wake models including different numbers of POD modes. It is shown that approximately six POD modes are enough to capture the load dynamics on large temporal scales. Modeling the weighting coefficients as independent stochastic processes leads to similar load characteristics as in the case of the truncated POD. To complete this simplified wake description, we show evidence that the small-scale dynamics can be captured by adding to our model a homogeneous turbulent field. In this way, we present a procedure to derive stochastic wake models from costly computational fluid dynamics (CFD calculations or elaborated experimental investigations. These numerically efficient models provide the added value of possible long-term studies. Depending on the aspects of interest, different minimalized models may be obtained.

  9. Expected Effects of Offshore Wind Farms on Mediterranean Marine Life

    Directory of Open Access Journals (Sweden)

    Laura Bray

    2016-03-01

    Full Text Available Current climate policy and issues of energy security mean wind farms are being built at an increasing rate to meet energy demand. As wind farm development is very likely in the Mediterranean Sea, we provide an assessment of the offshore wind potential and identify expected biological effects of such developments in the region. We break new ground here by identifying potential offshore wind farm (OWF “hotspots” in the Mediterranean. Using lessons learned in Northern Europe, and small-scale experiments in the Mediterranean, we identify sensitive species and habitats that will likely be influenced by OWFs in both these hotspot areas and at a basin level. This information will be valuable to guide policy governing OWF development and will inform the industry as and when environmental impact assessments are required for the Mediterranean Sea.

  10. Denmark Wind Energy Programme

    DEFF Research Database (Denmark)

    Shen, Wen Zhong

    2015-01-01

    In this chapter, a summary of some ongoing wind energy projects in Denmark is given. The research topics comprise computational model development, wind turbine (WT) design, low-noise airfoil and blade design, control device development, wake modelling and wind farm layout optimization....

  11. Health effects and wind turbines: A review of the literature

    Directory of Open Access Journals (Sweden)

    Ollson Christopher A

    2011-09-01

    Full Text Available Abstract Background Wind power has been harnessed as a source of power around the world. Debate is ongoing with respect to the relationship between reported health effects and wind turbines, specifically in terms of audible and inaudible noise. As a result, minimum setback distances have been established world-wide to reduce or avoid potential complaints from, or potential effects to, people living in proximity to wind turbines. People interested in this debate turn to two sources of information to make informed decisions: scientific peer-reviewed studies published in scientific journals and the popular literature and internet. Methods The purpose of this paper is to review the peer-reviewed scientific literature, government agency reports, and the most prominent information found in the popular literature. Combinations of key words were entered into the Thomson Reuters Web of KnowledgeSM and the internet search engine Google. The review was conducted in the spirit of the evaluation process outlined in the Cochrane Handbook for Systematic Reviews of Interventions. Results Conclusions of the peer reviewed literature differ in some ways from those in the popular literature. In peer reviewed studies, wind turbine annoyance has been statistically associated with wind turbine noise, but found to be more strongly related to visual impact, attitude to wind turbines and sensitivity to noise. To date, no peer reviewed articles demonstrate a direct causal link between people living in proximity to modern wind turbines, the noise they emit and resulting physiological health effects. If anything, reported health effects are likely attributed to a number of environmental stressors that result in an annoyed/stressed state in a segment of the population. In the popular literature, self-reported health outcomes are related to distance from turbines and the claim is made that infrasound is the causative factor for the reported effects, even though sound pressure

  12. Health effects and wind turbines: a review of the literature.

    Science.gov (United States)

    Knopper, Loren D; Ollson, Christopher A

    2011-09-14

    Wind power has been harnessed as a source of power around the world. Debate is ongoing with respect to the relationship between reported health effects and wind turbines, specifically in terms of audible and inaudible noise. As a result, minimum setback distances have been established world-wide to reduce or avoid potential complaints from, or potential effects to, people living in proximity to wind turbines. People interested in this debate turn to two sources of information to make informed decisions: scientific peer-reviewed studies published in scientific journals and the popular literature and internet. The purpose of this paper is to review the peer-reviewed scientific literature, government agency reports, and the most prominent information found in the popular literature. Combinations of key words were entered into the Thomson Reuters Web of KnowledgeSM and the internet search engine Google. The review was conducted in the spirit of the evaluation process outlined in the Cochrane Handbook for Systematic Reviews of Interventions. Conclusions of the peer reviewed literature differ in some ways from those in the popular literature. In peer reviewed studies, wind turbine annoyance has been statistically associated with wind turbine noise, but found to be more strongly related to visual impact, attitude to wind turbines and sensitivity to noise. To date, no peer reviewed articles demonstrate a direct causal link between people living in proximity to modern wind turbines, the noise they emit and resulting physiological health effects. If anything, reported health effects are likely attributed to a number of environmental stressors that result in an annoyed/stressed state in a segment of the population. In the popular literature, self-reported health outcomes are related to distance from turbines and the claim is made that infrasound is the causative factor for the reported effects, even though sound pressure levels are not measured. What both types of studies

  13. Variations of the wake height over the Bolund escarpment

    DEFF Research Database (Denmark)

    Lange, Julia; Mann, Jakob; Angelou, Nikolas

    2015-01-01

    lidar. The instrument measures the line-of-sight wind speed 390 times per second in highly resolved 7-m tall profiles by rapidly changing the focus distance and beam direction. The profiles reveal the detailed and rapidly changing structure of the wake induced by the Bolund escarpment. The wake grows...

  14. Evaluating Tilt for Wind Plants

    Energy Technology Data Exchange (ETDEWEB)

    Annoni, Jennifer [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Scholbrock, Andrew K. [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Churchfield, Matthew J. [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Fleming, Paul A. [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-07-03

    The objective of this work is to demonstrate the feasibility of tilt in a wind plant. Tilt control, much like other wind plant control strategies, has the potential to improve the performance of a wind plant. Tilt control uses the tilt angle of the turbine to direct the wake above or below the downstream turbines. This paper presents a study of tilt in two- and three-turbine arrays. Specifically, the authors show that the power production of a two-turbine array can be increased by tilting turbines in a specific orientation. When adding more turbines, as is shown with the three-turbine array, the overall percentage of power gain increases. This outcome deviates from some of the results seen in typical wind plant control strategies. Finally, we discuss the impact this type of control strategy has on the aerodynamics in a wind plant. This analysis demonstrates that a good understanding of wake characteristics is necessary to improve the plant's performance. A tilt strategy such as the one presented in this paper may have implications for future control/optimization studies including optimization of hub heights in a wind plant and analysis of deep array effects.

  15. LES investigation of infinite staggered wind-turbine arrays

    International Nuclear Information System (INIS)

    Yang, Xiaolei; Sotiropoulos, Fotis

    2014-01-01

    The layouts of turbines affect the turbine wake interactions and thus the wind farm performance. The wake interactions in infinite staggered wind-turbine arrays are investigated and compared with infinite aligned turbine arrays in this paper. From the numerical results we identify three types of wake behaviours, which are significantly different from wakes in aligned wind-turbine arrays. For the first type, each turbine wake interferes with the pair of staggered downstream turbine wakes and the aligned downstream turbine. For the second type, each turbine wake interacts with the first two downstream turbine wakes but does not show significant interference with the second aligned downstream turbine. For the third type, each turbine wake recovers immediately after passing through the gap of the first two downstream turbines and has little interaction with the second downstream turbine wakes The extracted power density and power efficiency are also studied and compared with aligned wind-turbine arrays

  16. Effects of amphetamine and modafinil on the sleep/wake cycle during experimental hypersomnia induced by sleep deprivation in the cat.

    Science.gov (United States)

    Lin, J S; Gervasoni, D; Hou, Y; Vanni-Mercier, G; Rambert, F; Frydman, A; Jouvet, M

    2000-03-01

    Modafinil is a newly discovered waking substance now being used in the treatment of hypersomnia and narcolepsy. We have shown previously in the cat that, unlike amphetamine, modafinil induces long-lasting wakefulness (W) without behavioral excitation and subsequent sleep rebound, and that its waking effect does not depend on endogenous catecholamines. To further characterize the awakening properties of modafinil and current psychostimulants in experimental models of hypersomnia, we examined the effect of oral administration of placebo, modafinil (5 mg kg-1) or amphetamine (1 mg kg-1) on the sleep/wake cycle and power spectral density (PSD) in cats after an 18-h water-tank sleep deprivation period. We found that the placebo had no effect on the dynamics of sleep recovery, while both modafinil and amphetamine induced suppression of cortical slow activity and a waking state lasting 6-8 h. After the amphetamine-induced waking period, both deep slow wave sleep (SWS2) and paradoxical sleep (PS) occurred in greater amounts than after placebo and the PSD during SWS was also increased. Thus, the cumulative time spent in W during a 48-h period was similar to that with placebo, indicating enhanced sleep rebound. In contrast, after the modafinil-induced W, the occurrence and evolution of SWS2 or PS, as well as the PSD during SWS, were similar to those seen with placebo during the same period, so that the total time spent in W in a 48-h period remained significantly higher than the control level, indicating no additional sleep rebound. These results indicate that modafinil is effective against somnolence and hypersomnia and does not produce a subsequent increase in sleep and suggest that the pharmacological profile of modafinil is different from that of amphetamine.

  17. Compliance effects on dynamically pitching wind turbine airfoils

    Science.gov (United States)

    Magstadt, Andrew S.

    The effects of elastic compliance in dynamically pitching wind turbine blades have been investigated. A numerical model guided wind tunnel testing, which used unsteady surface pressure measurements and phase-locked Particle Imaging Velocimetry to gather aerodynamic information. Using a torsionally compliant member, aeroelastic effects on the unsteady aerodynamics were compared against the results from a corresponding rigidly pitching airfoil to isolate the effects of compliance. The novel experimental apparatus and data acquisition techniques developed at the University of Wyoming showed that the presence of compliance can alter flow-field structures and increase dynamic loading. The high sensitivity of this nonlinear system suggests the formation of fluid-structure instabilities in large-scale turbines and demonstrates the potential for aerodynamic control as a means to mitigate adverse loading effects and improve wind turbine efficiency.

  18. Numerical Investigation of Wind Conditions for Roof-Mounted Wind Turbines: Effects of Wind Direction and Horizontal Aspect Ratio of a High-Rise Cuboid Building

    Directory of Open Access Journals (Sweden)

    Takaaki Kono

    2016-11-01

    Full Text Available From the viewpoint of installing small wind turbines (SWTs on rooftops, this study investigated the effects of wind direction and horizontal aspect ratio (HAR = width/length of a high-rise cuboid building on wind conditions above the roof by conducting large eddy simulations (LESs. The LES results confirmed that as HAR decreases (i.e., as the building width decreases, the variation in wind velocity over the roof tends to decrease. This tendency is more prominent as the angle between the wind direction and the normal vector of the building’s leeward face with longer roof edge increases. Moreover, at windward corners of the roof, wind conditions are generally favorable at relatively low heights. In contrast, at the midpoint of the roof's windward edge, wind conditions are generally not favorable at relatively low heights. At leeward representative locations of the roof, the bottoms of the height range of favorable wind conditions are typically higher than those at the windward representative locations, but the favorable wind conditions are much better at the leeward representative locations. When there is no prevailing wind direction, the center of the roof is more favorable for installing SWTs than the corners or the edge midpoints of the roof.

  19. Performance and wake conditions of a rotor located in the wake of an obstacle

    DEFF Research Database (Denmark)

    Naumov, I. V.; Kabardin, I. K.; Mikkelsen, Robert Flemming

    2016-01-01

    to the rotor was changed from 4 to 8 rotor diameters, with the vertical distance from the rotor axis varied 0.5 and 1 rotor diameters. The associated turbulent intensity of the incoming flow to the rotor changed 3 to '6% due to the influence of the disk wake. In the experiment, thrust characteristics......, PIV measurements were carried out to study the development of the mean velocity deficit profiles of the wake behind the wind turbine model under the influence of the wake generated by the obstacle. By use of regression techniques to fit the velocity profiles it was possible to determine velocity...

  20. Wake field accelerators

    International Nuclear Information System (INIS)

    Wilson, P.B.

    1986-02-01

    In a wake field accelerator a high current driving bunch injected into a structure or plasma produces intense induced fields, which are in turn used to accelerate a trailing charge or bunch. The basic concepts of wake field acceleration are described. Wake potentials for closed cavities and periodic structures are derived, as are wake potentials on a collinear path with a charge distribution. Cylindrically symmetric structures excited by a beam in the form of a ring are considered

  1. Beam emittance and the effects of the rf, space charge and wake fields: Application to the ATF photoelectron beam

    International Nuclear Information System (INIS)

    Parsa, Z.

    1991-01-01

    Laser driven photoelectron guns are of interest for use in new methods of accelerations, future development of Linear Colliders and new experiments such as Free Electron laser (IFEL). Such guns are potential source of low emittance-high current and short bunch length electron beams, where the emitted electrons are accelerated quickly to a relativistic energy by a strong rf, electric field in the cavity. We present a brief overview of the beam dynamic studies, e.g. emittance for the Brookhaven National Laboratory (BNL) ATF high brightness photocathode radio frequency gun (now in operation), and show the effects of the rf, Space Charge, and Wake fields on the photoelectrons. 4 refs., 7 figs

  2. Effect of High Porosity Screen on the Near Wake of a Circular Cylinder

    Directory of Open Access Journals (Sweden)

    Sahin B.

    2013-04-01

    Full Text Available The change in flow characteristics downstream of a circular cylinder (inner cylinder surrounded by a permeable cylinder (outer cylinder made of a high porosity screen was investigated in shallow water using Particle Image Velocimetry (PIV technique. The diameter of the inner cylinder, outer cylinder and the water height were kept constant during the experiments as d = 50 mm, D = 100 mm and hw = 50 mm, respectively. The depth-averaged free stream velocity was also kept constant as U = 180 mm/s which corresponded to a Reynolds number of Red = 9000 based on the inner cylinder diameter. It was shown that the outer permeable cylinder had a substantialeffect on the vortex formation and consequent vortex shedding downstream of the circular cylinder, especially in the near wake. The time averaged vorticity layers, streamlines and velocity vector field depict that the location of the interaction of vortices considerably changed by the presence of the outer cylinder. Turbulent statistics clearly demonstrated that in comparison to the natural cylinder, turbulent kinetic energy and Reynolds stresses decreased remarkably downstream of the inner cylinder. Moreover, spectra of streamwise velocity fluctuations showed that the vortex shedding frequency significantly reduced compared to the natural cylinder case.

  3. Thermal effects influencing measurements in a supersonic blowdown wind tunnel

    Directory of Open Access Journals (Sweden)

    Vuković Đorđe S.

    2016-01-01

    Full Text Available During a supersonic run of a blowdown wind tunnel, temperature of air in the test section drops which can affect planned measurements. Adverse thermal effects include variations of the Mach and Reynolds numbers, variation of airspeed, condensation of moisture on the model, change of characteristics of the instrumentation in the model, et cetera. Available data on thermal effects on instrumentation are pertaining primarily to long-run-duration wind tunnel facilities. In order to characterize such influences on instrumentation in the models, in short-run-duration blowdown wind tunnels, temperature measurements were made in the wing-panel-balance and main-balance spaces of two wind tunnel models tested in the T-38 wind tunnel. The measurements showed that model-interior temperature in a run increased at the beginning of the run, followed by a slower drop and, at the end of the run, by a large temperature drop. Panel-force balance was affected much more than the main balance. Ways of reducing the unwelcome thermal effects by instrumentation design and test planning are discussed.

  4. Effects of a newly developed potent orexin-2 receptor-selective antagonist Compound1m on sleep/wake states in mice

    Directory of Open Access Journals (Sweden)

    Keishi eEtori

    2014-01-01

    Full Text Available Orexins (also known as hypocretins, which are hypothalamic neuropeptides, play critical roles in the regulation of sleep/wakefulness states by activating two G-protein coupled receptors (GPCRs, orexin 1 (OX1R and orexin 2 receptors (OX2R. In order to know the difference between effects of OX2R-selective antagonists (2-SORA and dual orexin receptor antagonists (DORA, and to understand the mechanisms underlying orexin-mediated regulation of sleep/wakefulness states, we examined the effects of a newly developed 2-SORA, Compound 1m (C1m, and a DORA, suvorexant, on sleep/wakefulness states in C57BL/6J mice. After oral administration in the dark period, both C1m and suvorexant exhibited potent sleep-promoting properties with similar efficacy in a dose-dependent manner. While C1m did not increase NREM and REM sleep episode durations, suvorexant induced longer episode durations of NREM and REM sleep as compared with both the vehicle- and C1m-administered groups. When compounds were injected during light period, C1m did not show a significant change in sleep/wakefulness states in the light period, whereas suvorexant slightly but significantly increased the sleep time. We also found that C1m did not affect the time of REM sleep, while suvorexant markedly increased it. This suggests that although OX1R-mediated pathway plays a pivotal role in promoting wakefulness, OX1R-mediated pathway also plays an additional role. OX1R-mediated pathway also plays a role in suppression of REM sleep. Fos-immunostaining showed that both compounds affected the activity of arousal-related neurons with different patterns. These results suggest partly overlapping and partly distinct roles of orexin receptors in the regulation of sleep/wakefulness states.

  5. Passive Control of Flow behind a Two-dimensional Model Vehicle for Drag Reduction Using Wake Disrupter

    Science.gov (United States)

    Choi, Haecheon; Park, Hyungmin; Choi, Jin; Jeon, Woo-Pyung

    2004-11-01

    A wind-tunnel experiment is performed to control flow behind a two-dimensional model vehicle, which has a fixed separation point, with a newly proposed passive device, wake disrupter. The wake disrupter is a small-size rectangular body attached to the upper and lower trailing edges, designed to perturb an essentially two-dimensional nature of wake. The effect of the wake disrupter on the base pressure of the model vehicle is tested for various configurations by varying its size and spanwise spacing. The experiments are conducted at the Reynolds numbers of 20000, 40000 and 80000 based on the free stream velocity and model height. The optimal configuration of wake disrupter produces 33% increase in the base pressure, whose amount is much larger than that by single optimal pair(22%). A hot-wire measurement is also carried out to examine the characteristics of turbulent flow disturbed by the wake disrupter. It shows that the wake disrupter significantly increases the length and width of vortex formation along the entire spanwise direction, which is closely related to the pressure recovery at the base surface.

  6. NUMERICAL SIMULATION AND EXPERIMENTAL STUDIES ON AFT HULL LOCAL PARAMETERIZED NON-GEOSIM DEFORMATION FOR CORRECTING SCALE EFFECTS OF NOMINAL WAKE FIELD

    Directory of Open Access Journals (Sweden)

    Tiecheng Wu

    2017-01-01

    Full Text Available The scale effects of an aft hull wake field pose a great challenge to propeller design and its performance prediction. Research into the characteristics of the scale effects and the subsequent correction of the errors caused by such effects play an important role in improving a ship’s energy conservation and propulsion performance. For this research, using a KCS ship as the research target, the aft shape of an original ship model has been modified based on the smart dummy model (SDM to change its nominal wake field. The present study explores the aft hull deformation of a KCS ship through a series of numerical calculations and validates the results using a similar ship model. In addition, wake field PIV-measurements are performed using particle image velocimetry to verify the corrected effects of the SDM. The SDM correction method offers a new pathway for correcting the errors associated with the scale effects in the nominal wake field measurements of a ship model.

  7. Analysing wind farm efficiency on complex terrains

    International Nuclear Information System (INIS)

    Castellani, Francesco; Astolfi, Davide; Terzi, Ludovico; Hansen, Kurt Schaldemose; Rodrigo, Javier Sanz

    2014-01-01

    Actual performances of onshore wind farms are deeply affected both by wake interactions and terrain complexity: therefore monitoring how the efficiency varies with the wind direction is a crucial task. Polar efficiency plot is therefore a useful tool for monitoring wind farm performances. The approach deserves careful discussion for onshore wind farms, where orography and layout commonly affect performance assessment. The present work deals with three modern wind farms, owned by Sorgenia Green, located on hilly terrains with slopes from gentle to rough. Further, onshore wind farm of Nprrekffir Enge has been analysed as a reference case: its layout is similar to offshore wind farms and the efficiency is mainly driven by wakes. It is shown and justified that terrain complexity imposes a novel and more consistent way for defining polar efficiency. Dependency of efficiency on wind direction, farm layout and orography is analysed and discussed. Effects of atmospheric stability have been also investigated through MERRA reanalysis data from NASA satellites. Monin-Obukhov Length has been used to discriminate climate regimes

  8. Next Generation Fiber Coherent Lidar System for Wake Vortex Detection, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — SibellOptics proposes to develop an eye-safe, long-range, compact, versatile, all-fiber wind LIDAR system for wake vortex measurement and other wind measurement...

  9. The effects of melatonin on sleep-wake rhythm of daytime haemodialysis patients: A randomized, placebo-controlled, cross-over study (EMSCAP study)

    NARCIS (Netherlands)

    Koch, B.C.P.; Nagtegaal, J.E.; Hagen, E.C.; van der Westerlaken, M.M.L; Boringa, J.B.S.; Kerkhof, G.A.; ter Wee, P.M.

    2009-01-01

    AIM: The aim of this study was to investigate the effects of exogenous melatonin on sleep-wake rhythm in haemodialysis patients. METHODS: The study design is a randomized, double-blind, placebo-controlled, cross-over study of 3 ¥ 6 weeks melatonin 3 mg at 22.00 h every night. Haemodialysis patients

  10. Effects of wind-energy facilities on grassland bird distributions

    Science.gov (United States)

    Shaffer, Jill A.; Buhl, Deb

    2016-01-01

    The contribution of renewable energy to meet worldwide demand continues to grow. Wind energy is one of the fastest growing renewable sectors, but new wind facilities are often placed in prime wildlife habitat. Long-term studies that incorporate a rigorous statistical design to evaluate the effects of wind facilities on wildlife are rare. We conducted a before-after-control-impact (BACI) assessment to determine if wind facilities placed in native mixed-grass prairies displaced breeding grassland birds. During 2003–2012, we monitored changes in bird density in 3 study areas in North Dakota and South Dakota (U.S.A.). We examined whether displacement or attraction occurred 1 year after construction (immediate effect) and the average displacement or attraction 2–5 years after construction (delayed effect). We tested for these effects overall and within distance bands of 100, 200, 300, and >300 m from turbines. We observed displacement for 7 of 9 species. One species was unaffected by wind facilities and one species exhibited attraction. Displacement and attraction generally occurred within 100 m and often extended up to 300 m. In a few instances, displacement extended beyond 300 m. Displacement and attraction occurred 1 year after construction and persisted at least 5 years. Our research provides a framework for applying a BACI design to displacement studies and highlights the erroneous conclusions that can be made without the benefit of adopting such a design. More broadly, species-specific behaviors can be used to inform management decisions about turbine placement and the potential impact to individual species. Additionally, the avoidance distance metrics we estimated can facilitate future development of models evaluating impacts of wind facilities under differing land-use scenarios.

  11. Effect of wind turbine generator model and siting on wind power changes out of large WECS arrays

    Science.gov (United States)

    Schleuter, R. A.; Park, G. L.; Lotfalian, M.; Dorsey, J.; Shayanfar, H.

    1981-01-01

    Methods of reducing the WECS generation change through selection of the wind turbine model for each site, selection of an appropriate siting configuration, and wind array controls are discussed. An analysis of wind generation change from an echelon and a farm for passage of a thunderstorm is presented. Reduction of the wind generation change over ten minutes is shown to reduce the increase in spinning reserve, unloadable generation and load following requirements on unit commitment when significant WECS generation is present and the farm penetration constraint is satisfied. Controls on the blade pitch angle of all wind turbines in an array or a battery control are shown to reduce both the wind generation change out of an array and the effective farm penetration in anticipation of a storm so that the farm penetration constraint may be satisfied.

  12. [Sleep deprivation and its effect on the ability to maintain wakefulness: implications on functioning and driving].

    Science.gov (United States)

    Furman, Gabriela Dorfman; Cahan, Clement; Baharav, Armada

    2009-05-01

    During the last century, western society suffers from an increasing steep debt. A large number of accidents occur due to drowsy drivers. People are not aware of the influence of fatigue/drowsiness on their functioning and driving capacity. Our goal is to identify and characterize measurable physioLogicaL information capable of monitoring simple and reliable performance of driver vigilance. Eight healthy volunteers without sleep disorders were included in the study. They participated in two missions, on and off every two hours during 34-36 hours, in order to create an accumulative sleep debt. The tasks included the Maintenance of wakefulness test (MWT) and the driving simulator test. White tested, they remained connected to EEG, EMG, EOG, ECG and audio-video registration. These first results are related to 60 MWT tests. The first falling asleep events (FA) appeared around the early afternoon hours, in agreement to the physiological tendency to fall asleep, according to the biological clock. The night was characterized by FAs with a very short sleep Latency time at around 4 AM. On the second day of the experiment, the averaged sleep latency was larger than in the night before, despite the accumulation of sleep debt. The fluctuations of RRI increased after the first micro sleep. The autonomic nervous regulation displays an increase in the overall sympathetic activity as an indicator of increased stress. There is a correlation between parameters associated with instantaneous autonomic changes of heart rhythm (RRI) and the FA/almost-FA events observed on EEG. These attributes may provide a useful tool for monitoring drowsy drivers and preventing accidents.

  13. Flow structure in the locked-on wake of a circular cylinder in pulsating flow: Effect of forcing amplitude

    International Nuclear Information System (INIS)

    Konstantinidis, E.; Balabani, S.

    2008-01-01

    The wake structure of a circular cylinder in non-reversing pulsating flow is investigated by means of particle image velocimetry. Measurements are reported for pulsations at twice the natural frequency of vortex shedding in the unforced wake and for forcing amplitudes up to 23% at a constant Reynolds number of 2150. For the parameters employed the vortex shedding locks-on to the sub-harmonic of the pulsation frequency and a resonant wake is formed. The mean velocity field and the distributions of the total and coherent Reynolds stresses show that the averaged wake structure is systematically modified by the flow pulsations. It is shown that this modification is caused by changes in the dynamics of vortex formation and shedding primarily in the near wake. The recirculation bubble and the vortex formation region decrease in size, the global peak values in the distributions of the total and coherent Reynolds stresses increase asymptotically whereas the vortex strength and the mean drag coefficient increase almost linearly with increasing forcing amplitude. The measures of the minimum wake width in the formation region do not exhibit any variation with amplitude even though the wake downstream of the formation region is wider in pulsating flow due to the increased strength of the shed vortices

  14. Sleep Pharmacogenetics: Personalized Sleep-Wake Therapy.

    Science.gov (United States)

    Holst, Sebastian C; Valomon, Amandine; Landolt, Hans-Peter

    2016-01-01

    Research spanning (genetically engineered) animal models, healthy volunteers, and sleep-disordered patients has identified the neurotransmitters and neuromodulators dopamine, serotonin, norepinephrine, histamine, hypocretin, melatonin, glutamate, acetylcholine, γ-amino-butyric acid, and adenosine as important players in the regulation and maintenance of sleep-wake-dependent changes in neuronal activity and the sleep-wake continuum. Dysregulation of these neurochemical systems leads to sleep-wake disorders. Most currently available pharmacological treatments are symptomatic rather than causal, and their beneficial and adverse effects are often variable and in part genetically determined. To evaluate opportunities for evidence-based personalized medicine with present and future sleep-wake therapeutics, we review here the impact of known genetic variants affecting exposure of and sensitivity to drugs targeting the neurochemistry of sleep-wake regulation and the pathophysiology of sleep-wake disturbances. Many functional polymorphisms modify drug response phenotypes relevant for sleep. To corroborate the importance of these and newly identified variants for personalized sleep-wake therapy, human sleep pharmacogenetics should be complemented with pharmacogenomic investigations, research about sleep-wake-dependent pharmacological actions, and studies in mice lacking specific genes. These strategies, together with future knowledge about epigenetic mechanisms affecting sleep-wake physiology and treatment outcomes, may lead to potent and safe novel therapies for the increasing number of sleep-disordered patients (e.g., in aged populations).

  15. External effects related to biogas and wind power

    DEFF Research Database (Denmark)

    Ibsen, Liselotte Schleisner; Nielsen, Per Sieverts

    1998-01-01

    will focus on estimates of externalities related to wind and biogas energy supplies using the ExternE methodology developed in a major study launched by the European Comission. External costs are the costs imporsed on society that are not included in the market price (e.g. effects of air pollution on health......Energy produced by wind power and biogas is today more expensive than energy produced by fossil fuels. However, by including external costs related to the technologies, the renewable technologies are expected to result in social benefits compared to the conventional power technologies. The paper...

  16. Aeroelastic modal dynamics of wind turbines including anisotropic effects

    DEFF Research Database (Denmark)

    Skjoldan, Peter Fisker

    and the computationally efficient implicit Floquet analysis in anisotropic conditions. The tool is validated against system identifications with the partial Floquet method on the nonlinear BHawC model of a 2.3 MW wind turbine. System identification results show that nonlinear effects on the 2.3 MW turbine in most cases....... These harmonics appear in calculated frequency responses of the turbine. Extreme wind shear changes the modal damping when the flow is separated due to an interaction between the periodic mode shape and the local aerodynamic damping influenced by a periodic variation in angle of attack....

  17. Impact of Wind Shear and Tower Shadow Effects on Power System with Large Scale Wind Power Penetration

    DEFF Research Database (Denmark)

    Hu, Weihao; Su, Chi; Chen, Zhe

    2011-01-01

    presents a simulation model of a variable speed wind farm with permanent magnet synchronous generators (PMSGs) and fullscale back-to-back converters in the simulation tool of DIgSILENT/PowerFactory. In this paper, the impacts of wind shear and tower shadow effects on the small signal stability of power...

  18. Effects of structure flexibility on horizontal axis wind turbine performances

    Science.gov (United States)

    Coiro, D. P.; Daniele, E.; Scherillo, F.

    2013-10-01

    This work illustrates the effects of flexibility of rotor blades and turbine tower on the performances of an horizontal axis wind turbine (HAWT) designed by our ADAG research group, by means of several example applied on a recent project for a active pitch controlled upwind 60 kW HAWT. The influence of structural flexibility for blade only, tower only and blade coupled with tower configuration is investigated using an aero-elastic computer-aided engineering (CAE) tool for horizontal axis wind turbines named FAST developed at National Renewable Energy Laboratory (NREL) of USA. For unsteady inflow conditions in front of the isolated HAWT the performances in rigid and flexible operation mode are computed and compared in order to illustrate the limitation included within a classical rigid body approach to wind turbine simulation.

  19. The Effect of Wind Power Installations on Coastal Tourism

    Directory of Open Access Journals (Sweden)

    Willett Kempton

    2010-01-01

    Full Text Available We surveyed more than 1,000 randomly sampled, out-of-state tourists at Delaware, USA beaches in 2007. After providing respondents with wind turbine project photo-simulations at several distances, we inquired about the effect development would have on visitation. Approximately one-quarter stated that they would switch beaches if an offshore wind project was located 10 km from the coast, with avoidance diminishing with greater distance from shore. Stated avoidance is less than: avoidance with a fossil fuel power plant located the same distance inland; attraction to a beach with offshore wind turbines; and the percentage stating they would likely pay to take a boat tour.

  20. Variability and smoothing effect of wind power production compared to load variability in the Nordic countries

    DEFF Research Database (Denmark)

    Holttinen, Hannele; Rissanen, Simo; Giebel, Gregor

    2012-01-01

    the viewpoint of wind integration. The smoothing effect is shown as reduction of variability from a single country to Nordic wide wind power. The impact of wind power on the variability that the system sees is depicted by analysing the variability of net load with different wind power penetration levels...

  1. Optimization Under Uncertainty for Wake Steering Strategies: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Quick, Julian [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Annoni, Jennifer [National Renewable Energy Laboratory (NREL), Golden, CO (United States); King, Ryan N [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Dykes, Katherine L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Fleming, Paul A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Ning, Andrew [Brigham Young University

    2017-05-01

    Wind turbines in a wind power plant experience significant power losses because of aerodynamic interactions between turbines. One control strategy to reduce these losses is known as 'wake steering,' in which upstream turbines are yawed to direct wakes away from downstream turbines. Previous wake steering research has assumed perfect information, however, there can be significant uncertainty in many aspects of the problem, including wind inflow and various turbine measurements. Uncertainty has significant implications for performance of wake steering strategies. Consequently, the authors formulate and solve an optimization under uncertainty (OUU) problem for finding optimal wake steering strategies in the presence of yaw angle uncertainty. The OUU wake steering strategy is demonstrated on a two-turbine test case and on the utility-scale, offshore Princess Amalia Wind Farm. When we accounted for yaw angle uncertainty in the Princess Amalia Wind Farm case, inflow-direction-specific OUU solutions produced between 0% and 1.4% more power than the deterministically optimized steering strategies, resulting in an overall annual average improvement of 0.2%. More importantly, the deterministic optimization is expected to perform worse and with more downside risk than the OUU result when realistic uncertainty is taken into account. Additionally, the OUU solution produces fewer extreme yaw situations than the deterministic solution.

  2. A Comparative Analysis on the Response of a Wind-Turbine Model to Atmospheric and Terrain Effects

    Science.gov (United States)

    Howard, K. B.; Chamorro, L. P.; Guala, M.

    2016-02-01

    In a series of wind-tunnel experiments conducted at the St. Anthony Falls Laboratory, a wind-turbine model was exposed to three different thermal regimes (neutral, weakly stable and weakly convective flows) in three simple arrangements relevant to wind-farm applications: single turbine in the boundary-layer, aligned turbine-turbine, and an upwind three-dimensional sinusoidal hill aligned with the turbine. Results focus on the spatial evolution of large-scale motions developing over the different thermal and topographic boundary conditions, and on their influence on the mean and fluctuating angular velocity of the turbine rotor. As compared to the single turbine case, both the upwind hill and turbine caused a reduction in the mean angular velocity regardless of the thermal regime; the turbine angular velocity fluctuations always decreased with a turbine upwind, which depleted the energy of the large structures of the flow; however such fluctuations decreased (increased) under stably stratified (convective) conditions when the hill was present. Pre-multiplied spectra of the rotor angular velocity and two-point correlation contours of the streamwise velocity component confirmed a non-trivial link between thermal stratification and terrain complexity. It is inferred that the thermal effects occurring in the three different boundary-layer regimes modulate the spanwise motion of the hill wake and define whether the hill shelters or exposes the turbine to enhanced large-scale energetic motions.

  3. The Effects of Modafinil on Aviator Performance During 40 Hours of Continuous Wakefulness: A UH-60 Helicopter Simulator Study

    National Research Council Canada - National Science Library

    Caidwell, John

    1999-01-01

    ...) activation in helicopter pilots who had been deprived of sleep. Six Army helicopter pilots were each exposed to two 40-hour periods of continuous wakefulness separated by one night of recovery sleep...

  4. Wind energy and electricity prices. Exploring the 'merit order effect'

    International Nuclear Information System (INIS)

    Morthost, P.E.; Ray, S.; Munksgaard, J.; Sinner, A.F.

    2010-04-01

    This report focuses on the effect of wind energy on the electricity price in the power market. As the report will discuss, adding wind into the power mix has a significant influence on the resulting price of electricity, the so called merit order effect (MOE). The merit order effect has been quantified and discussed in many scientific publications. This report ends the first phase of a study on the MOE, evaluating the impact of EWEA's 2020 scenarios on future European electricity prices. The basic principles of the merit order effect are provided in the first part of the document. The literature review itself contains methods and tools not only to quantify the merit order effect but also in order to forecast its future range and volume.

  5. Optimization of wind farm micro-siting for complex terrain using greedy algorithm

    International Nuclear Information System (INIS)

    Song, M.X.; Chen, K.; He, Z.Y.; Zhang, X.

    2014-01-01

    An optimization approach based on greedy algorithm for optimization of wind farm micro-siting is presented. The key of optimizing wind farm micro-siting is the fast and accurate evaluation of the wake flow interactions of wind turbines. The virtual particle model is employed for wake flow simulation of wind turbines, which makes the present method applicable for non-uniform flow fields on complex terrains. In previous bionic optimization method, within each step of the optimization process, only the power output of the turbine that is being located or relocated is considered. To aim at the overall power output of the wind farm comprehensively, a dependent region technique is introduced to improve the estimation of power output during the optimization procedure. With the technique, the wake flow influences can be reduced more efficiently during the optimization procedure. During the optimization process, the turbine that is being added will avoid being affected other turbines, and avoid affecting other turbine in the meantime. The results from the numerical calculations demonstrate that the present method is effective for wind farm micro-siting on complex terrain, and it produces better solutions in less time than the previous bionic method. - Highlights: • Greedy algorithm is applied to wind farm micro-siting problem. • The present method is effective for optimization on complex terrains. • Dependent region is suggested to improve the evaluation of wake influences. • The present method has better performance than the bionic method

  6. Building-wake diffusion

    International Nuclear Information System (INIS)

    Ramsdell, J.V.

    1988-01-01

    A recent review of building-wake diffusion models compares model predictions of centerline concentrations in building wakes with concentrations observed in experiments at seven nuclear reactors. In general, the model predictions are conservative in that they tend to predict concentrations that are greater than those actually observed. However, the models show little skill in accounting for variations in the observed concentrations. Analysis of experimental data indicates that the general form of the standard wake diffusion models is inconsistent with observed variations of concentrations in the wakes. The inconsistency is especially marked for ground-level releases. As an interim measure, multiple linear regression techniques have been used to develop a statistical building-wake model alternative to the current models. This paper describes the statistical wake model and compares it with other models

  7. Evaluation of the effect of chronic exposure to 137Cesium on sleep-wake cycle in rats

    International Nuclear Information System (INIS)

    Lestaevel, Philippe; Dhieux, Bernadette; Tourlonias, Elie; Houpert, Pascale; Paquet, Francois; Voisin, Philippe; Aigueperse, Jocelyne; Gourmelon, Patrick

    2006-01-01

    Since the Chernobyl accident, the most significant problem for the population living in the contaminated areas is chronic exposure by ingestion of radionuclides, notably 137 Cs, a radioactive isotope of cesium. It can be found in the whole body, including the central nervous system. The present study aimed to assess the effect of 137 Cs on the central nervous system and notably on open-field activity and the electroencephalographic pattern. Rats were exposed up to 90 days to drinking water contaminated with 137 Cs at a dosage of 400 Bq kg -1 , which is similar to that ingested by the population living in contaminated territories. At this level of exposure, no significant effect was observed on open-field activity. On the other hand, at 30 days exposure, 137 Cs decreased the number of episodes of wakefulness and slow wave sleep and increased the mean duration of these stages. At 90 days exposure, the power of 0.5-4 Hz band of 137 Cs-exposed rats was increased in comparison with controls. These electrophysiological changes may be due to a regional 137 Cs accumulation in the brain stem. In conclusion, the neurocognitive effects of 137 Cs need further evaluation and central disorders of population living in contaminated territories must be considered

  8. Effect of fall wind on wind power generation; Furyoku hatsuden ni okeru dashikaze no koka

    Energy Technology Data Exchange (ETDEWEB)

    Nagai, H. [Nihon University, Tokyo (Japan)

    1997-11-25

    Wind conditions in Arakawa Town, Niigata Prefecture, were surveyed by anemometers and anemoscopes installed at 3 different points, and the data are analyzed to develop the prediction model for investigating possibility of introduction of wind mills there. Outlined herein is power generated by fall wind by comparing predicted power availability with the actual results. In order to investigate possibility of power generation by fall wind, the wind conditions and power availability are simulated using the observed wind condition data. Predicted wind velocity involves a large error at a point where frequency of prevailing wind direction is high, and direction in which average wind velocity is high coincides with direction in which land is slanted at a high slope. Fall wind occurs locally for geographical reasons. Location of the wind mill must be carefully considered, because it is complex, although potentially gives a larger quantity of power. A wind mill of 400kW can produce power of around 600MWh annually, when it is located at the suited site confirmed by the wind condition analysis results. 6 refs., 5 figs., 6 tabs.

  9. Geo-effectiveness of Solar Wind Extremes

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle 23 presents a very special case during which many severe and strong effects were ...

  10. Experimental analysis on the dynamic wake of an actuator disc undergoing transient loads

    Science.gov (United States)

    Yu, W.; Hong, V. W.; Ferreira, C.; van Kuik, G. A. M.

    2017-10-01

    The Blade Element Momentum model, which is based on the actuator disc theory, is still the model most used for the design of open rotors. Although derived from steady cases with a fully developed wake, this approach is also applied to unsteady cases, with additional engineering corrections. This work aims to study the impact of an unsteady loading on the wake of an actuator disc. The load and flow of an actuator disc are measured in the Open Jet Facility wind tunnel of Delft University of Technology, for steady and unsteady cases. The velocity and turbulence profiles are characterized in three regions: the inner wake region, the shear layer region and the region outside the wake. For unsteady load cases, the measured velocity field shows a hysteresis effect in relation to the loading, showing differences between the cases when loading is increased and loading is decreased. The flow field also shows a transient response to the step change in loading, with either an overshoot or undershoot of the velocity in relation to the steady-state velocity. In general, a smaller reduced ramp time results in a faster velocity transient, and in turn a larger amplitude of overshoot or undershoot. Time constants analysis shows that the flow reaches the new steady-state slower for load increase than for load decrease; the time constants outside the wake are generally larger than at other radial locations for a given downstream plane; the time constants of measured velocity in the wake show radial dependence.The data are relevant for the validation of numerical models for unsteady actuator discs and wind turbines, and are made available in an open source database (see Appendix).

  11. A comparison of the effects of transcranial direct current stimulation and caffeine on vigilance and cognitive performance during extended wakefulness.

    Science.gov (United States)

    McIntire, Lindsey K; McKinley, R Andy; Goodyear, Chuck; Nelson, Justin

    2014-01-01

    Sleep deprivation from extended duty hours is a common complaint for many occupations. Caffeine is one of the most common countermeasures used to combat fatigue. However, the benefits of caffeine decline over time and with chronic use. Our objective was to evaluate the efficacy of anodal transcranial direct current stimulation (tDCS) applied to the pre-frontal cortex at 2 mA for 30 min to remediate the effects of sleep deprivation and to compare the behavioral effects of tDCS with those of caffeine. Three groups of 10 participants each received either active tDCS with placebo gum, caffeine gum with sham tDCS, or sham tDCS with placebo gum during 30 h of extended wakefulness. Our results show that tDCS prevented a decrement in vigilance and led to better subjective ratings for fatigue, drowsiness, energy, and composite mood compared to caffeine and control in sleep-deprived individuals. Both the tDCS and caffeine produced similar improvements in latencies on a short-term memory task and faster reaction times in a psychomotor task when compared to the placebo group. Interestingly, changes in accuracy for the tDCS group were not correlated to changes in mood; whereas, there was a relationship for the caffeine and sham groups. Our data suggest that tDCS could be a useful fatigue countermeasure and may be more beneficial than caffeine since boosts in performance and mood last several hours. Published by Elsevier Inc.

  12. Effects of extreme wind shear on aeroelastic modal damping of wind turbines

    DEFF Research Database (Denmark)

    Skjoldan, P.F.; Hansen, Morten Hartvig

    2013-01-01

    Wind shear is an important contributor to fatigue loads on wind turbines. Because it causes an azimuthal variation in angle of attack, it can also affect aerodynamic damping. In this paper, a linearized model of a wind turbine, based on the nonlinear aeroelastic code BHawC, is used to investigate...

  13. Proceedings of the ENDOW Workshop 'Offshore Wakes: measurements and Modelling'

    DEFF Research Database (Denmark)

    2002-01-01

    in Massachusetts, accuracy of SODAR measurements for wind energy and tidal influence of offshore wind speeds andturbulence. The papers presented in these Proceedings are the result of a workshop held at Risø National Laboratory on March 7 and 8 2002 entitled 'Offshore Wakes: Measurements and Modelling'....

  14. Dynamic Strategies for Yaw and Induction Control of Wind Farms Based on Large-Eddy Simulation and Optimization

    Directory of Open Access Journals (Sweden)

    Wim Munters

    2018-01-01

    Full Text Available In wind farms, wakes originating from upstream turbines cause reduced energy extraction and increased loading variability in downstream rows. The prospect of mitigating these detrimental effects through coordinated controllers at the wind-farm level has fueled a multitude of research efforts in wind-farm control. The main strategies in wind-farm control are to influence the velocity deficits in the wake by deviating from locally optimal axial induction setpoints on the one hand, and steering wakes away from downstream rows through yaw misalignment on the other hand. The current work investigates dynamic induction and yaw control of individual turbines for wind-farm power maximization in large-eddy simulations. To this end, receding-horizon optimal control techniques combined with continuous adjoint gradient evaluations are used. We study a 4 × 4 aligned wind farm, and find that for this farm layout yaw control is more effective than induction control, both for uniform and turbulent inflow conditions. Analysis of optimal yaw controls leads to the definition of two simplified yaw control strategies, in which wake meandering and wake redirection are exploited respectively. Furthermore it is found that dynamic yawing provides significant benefits over static yaw control in turbulent flow environments, whereas this is not the case for uniform inflow. Finally, the potential of combining overinductive axial induction control with yaw control is shown, with power gains that approximate the sum of those achieved by each control strategy separately.

  15. Flow adjustment inside large finite-size wind farms approaching the infinite wind farm regime

    Science.gov (United States)

    Wu, Ka Ling; Porté-Agel, Fernando

    2017-04-01

    Due to the increasing number and the growing size of wind farms, the distance among them continues to decrease. Thus, it is necessary to understand how these large finite-size wind farms and their wakes could interfere the atmospheric boundary layer (ABL) dynamics and adjacent wind farms. Fully-developed flow inside wind farms has been extensively studied through numerical simulations of infinite wind farms. The transportation of momentum and energy is only vertical and the advection of them is neglected in these infinite wind farms. However, less attention has been paid to examine the length of wind farms required to reach such asymptotic regime and the ABL dynamics in the leading and trailing edges of the large finite-size wind farms. Large eddy simulations are performed in this study to investigate the flow adjustment inside large finite-size wind farms in conventionally-neutral boundary layer with the effect of Coriolis force and free-atmosphere stratification from 1 to 5 K/km. For the large finite-size wind farms considered in the present work, when the potential temperature lapse rate is 5 K/km, the wind farms exceed the height of the ABL by two orders of magnitude for the incoming flow inside the farms to approach the fully-developed regime. An entrance fetch of approximately 40 times of the ABL height is also required for such flow adjustment. At the fully-developed flow regime of the large finite-size wind farms, the flow characteristics match those of infinite wind farms even though they have different adjustment length scales. The role of advection at the entrance and exit regions of the large finite-size wind farms is also examined. The interaction between the internal boundary layer developed above the large finite-size wind farms and the ABL under different potential temperature lapse rates are compared. It is shown that the potential temperature lapse rate plays a role in whether the flow inside the large finite-size wind farms adjusts to the fully

  16. Effect of Opening the Sash of a Centre-Pivot Roof Window on Wind Pressure Coefficients

    DEFF Research Database (Denmark)

    Iqbal, Ahsan; Wigö, Hans; Heiselberg, Per

    2014-01-01

    . The wind pressures were defined in terms of wind pressure coefficients. Traditionally wind pressure coefficients are extracted from the analysis of sealed plain surface. These wind pressure coefficients are used to estimate the natural ventilation rate through windows/openings due to wind effect. Surface...... averaged wind pressure coefficients do not accurately estimate the airflow rates. Therefore, local wind pressure coefficients are needed especially for dynamic calculation of airflow rates. From the wind tunnel experiments, it is concluded that outward opening the sash can significantly affect the wind...... pressure distribution nearby the window. The use of wind pressure coefficients from the analysis of sealed plain surface may lead to erroneous estimation of airflow rate....

  17. Effect of high wind conditions on AHX performance for PFBR

    International Nuclear Information System (INIS)

    Goyal, P.; Datta, Anu; Verma, Vishnu; Singh, R.K.

    2013-05-01

    In case of normal shut down or station blackout condition the core decay heat is removed by Safety Grade Decay Heat Removal System (SGDHRS) in PFBR. The Prototype Fast Breeder Reactor (PFBR) is under construction at Kalpakkam. SGDHRS remove decay heat from the core and dissipate it into the environment with the help of Air Heat Exchanger (AHX). SGDHRS consists of four redundant numbers of totally independent circuits capable of removing decay heat from the hot pool through natural convection in the primary and intermediate sodium sides as well as in the air side. Each circuit consists of a sodium to sodium heat exchanger (DHX) and a sodium to AHX connected to intermediate sodium circuit, AHX is located at a higher elevation compared to DHX. AHX is serpentine type finned tube compact heat exchanger with sodium in the tube side and air flowing over finned tubes. A tall stack provides the driving force for the natural convection of air flow through the AHX, when the dampers are opened. The AHX is placed outside of Reactor Control Building (RCB), on the roof of Steam Generator Building. Due to the presence of nearby buildings around the stack, the AHX performance under high wind condition may be affected. A CFD simulation using CFD-ACE+ code has been carried in which effect of high wind condition and nearby building on AHX performance have been studied. For high wind condition various orientation of wind movement was considered for parametric studies. AHX performance for all the cases were compared with the results that obtained for the absence of nearby buildings. A comparative table was prepared to understand how the AHX performance is effected with the high wind condition for various direction and with the presence of nearby building. It was observed that AHX performance is influenced by high wind conditions in most of the cases for with and without presence of nearby building. Hence to ensure the optimal performance of the AHX under high wind conditions its

  18. Wind tunnel experimental study on effect of inland nuclear power plant cooling tower on air flow and dispersion of pollutant

    International Nuclear Information System (INIS)

    Qiao Qingdang; Yao Rentai; Guo Zhanjie; Wang Ruiying; Fan Dan; Guo Dongping; Hou Xiaofei; Wen Yunchao

    2011-01-01

    A wind tunnel experiment for the effect of the cooling tower at Taohuajiang nuclear power plant on air flow and dispersion of pollutant was introduced in paper. Measurements of air mean flow and turbulence structure in different directions of cooling tower and other buildings were made by using an X-array hot wire probe. The effects of the cooling tower and its drift on dispersion of pollutant from the stack were investigated through tracer experiments. The results show that the effect of cooling tower on flow and dispersion obviously depends on the relative position of stack to cooling towers, especially significant for the cooling tower parallel to stack along wind direction. The variation law of normalized maximum velocity deficit and perturbations in longitudinal turbulent intensity in cooling tower wake was highly in accordance with the result of isolated mountain measured by Arya and Gadiyaram. Dispersion of pollutant in near field is significantly enhanced and plume trajectory is changed due to the cooling towers and its drift. Meanwhile, the effect of cooling tower on dispersion of pollutant depends on the height of release. (authors)

  19. Wake characterization downstream of a fog collector

    Science.gov (United States)

    Bresci, E.

    The problem of wake geometry characterization downstream of a collector for getting water out of advection fog is investigated combining the results coming from wind tunnel trials and an experimental campaign in Peru ( Lomas de Mejia), where a fog collection project was running. Results from a physical model of the fog collector at a 1:100 scale tested in a wind tunnel through anemometer velocity measurements and flow visualization techniques showed, at different heights from the ground, the general direction of the flow in the vicinity of the obstacle and the extension of the downstream-disturbed area. Wind speed data collection in Peru showed the reduction in wind speed depending on its intensity. The preliminary results show the utility of such an approach in order to improve the understanding of the flow motion downstream of permeable surfaces. The possibility of spatially characterizing the wake presence has a practical utilization whenever the knowledge of the geometry of the wake downstream of an obstacle is required.

  20. Estimation of the Possible Power of a Wind Farm

    DEFF Research Database (Denmark)

    Mirzaei, Mahmood; Göçmen Bozkurt, Tuhfe; Giebel, Gregor

    2014-01-01

    It seems possible to increase competitiveness of wind power plants by offering grid services (also called ancillary services) and enter the wind power plants into the ancillary market. One of the ancillary services is called reserve power, the differential capacity between the generated power...... and the available power in the farm. The total amount of energy that a wind farm can potentially generate is called possible power. It is very important for a wind farm owner to have a relatively accurate estimate of the possible power of the wind farm in order to be able to trade the reserve power. In this paper...... the possible power calculated based on the estimated effective wind speed of a down regulated wind farm (the industry standard) is compared against the calculated possible power based on the algorithm presented in the paper. The latter takes into account the eect of the wakes of down regulated turbines...

  1. Monitoring Wake Vortices for More Efficient Airports

    Science.gov (United States)

    2005-01-01

    Wake vortices are generated by all aircraft during flight. The larger the aircraft, the stronger the wake, so the Federal Aviation Administration (FAA) separates aircraft to ensure wake turbulence has no effect on approaching aircraft. Currently, though, the time between planes is often larger than it needs to be for the wake to dissipate. This unnecessary gap translates into arrival and departure delays, but since the wakes are invisible, the delays are nearly inevitable. If, however, the separation between aircraft can be reduced safely, then airport capacity can be increased without the high cost of additional runways. Scientists are currently studying these patterns to identify and introduce new procedures and technologies that safely increase airport capacity. NASA, always on the cutting edge of aerospace research, has been contributing knowledge and testing to these endeavors.

  2. Transient Thunderstorm Downbursts and Their Effects on Wind Turbines

    Directory of Open Access Journals (Sweden)

    Hieu H. Nguyen

    2014-10-01

    Full Text Available The International Electrotechnical Commission (IEC Standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of off-standard atmospheric conditions include thunderstorm downbursts, hurricanes, tornadoes, low-level jets, etc. The simulation of thunderstorm downbursts and associated loads on a utility-scale wind turbine is the focus of this study. Since the problem has not received sufficient attention, especially in terms of design, we thus focus in this paper on practical aspects. A wind field model that incorporates component non-turbulent and turbulent parts is described and employed in inflow simulations. The non-turbulent part is based on an available analytical model with some modifications, while the turbulent part is simulated as a stochastic process using standard turbulence power spectral density functions and coherence functions whose defining parameters are related to the downburst characteristics such as the storm translation velocity. Available information on recorded downbursts is used to define two storm scenarios that are studied. Rotor loads are generated using stochastic simulation of the aeroelastic response of a model of a utility-scale 5-MW turbine. An illustrative single storm simulation and the associated turbine response are used to discuss load characteristics and to highlight storm-related and environmental parameters of interest. Extensive simulations for two downbursts are then conducted while varying the storm’s location and track relative to the turbine. Results suggest that wind turbine yaw and pitch control systems clearly influence overall system response. Results also highlight the important effects of both the turbulence as well as the downburst mean wind profiles on turbine extreme loads.

  3. Wind turbine power curve prediction with consideration of rotational augmentation effects

    Science.gov (United States)

    Tang, X.; Huang, X.; Sun, S.; Peng, R.

    2016-11-01

    Wind turbine power curve expresses the relationship between the rotor power and the hub wind speed. Wind turbine power curve prediction is of vital importance for power control and wind energy management. To predict power curve, the Blade Element Moment (BEM) method is used in both academic and industrial communities. Due to the limited range of angles of attack measured in wind tunnel testing and the three-dimensional (3D) rotational augmentation effects in rotating turbines, wind turbine power curve prediction remains a challenge especially at high wind speeds. This paper presents an investigation of considering the rotational augmentation effects using characterized lift and drag coefficients from 3D computational fluid dynamics (CFD) simulations coupled in the BEM method. A Matlab code was developed to implement the numerical calculation. The predicted power outputs were compared with the NREL Phase VI wind turbine measurements. The results demonstrate that the coupled method improves the wind turbine power curve prediction.

  4. Effects of setting angle and chord length on performance of four blades bionic wind turbine

    Science.gov (United States)

    Yang, Z. X.; Li, G. S.; Song, L.; Bai, Y. F.

    2017-11-01

    With the energy crisis and the increasing environmental pollution, more and more efforts have been made about wind power development. In this paper, a four blades bionic wind turbine was proposed, and the outline of wind turbine was constructed by the fitted curve. This paper attempted to research the effects of setting angle and chord length on performance of four blades bionic wind turbine by computational fluid dynamics (CFD) simulation. The results showed that the setting angle and chord length of the bionic wind turbine has some significant effects on the efficiency of the wind turbine, and within the range of wind speed from 7 m/s to 15 m/s, the wind turbine achieved maximum efficiency when the setting angle is 31 degree and the chord length is 125 mm. The conclusion will work as a guideline for the improvement of wind turbine design

  5. Community investment in wind farms: funding structure effects in wind energy infrastructure development.

    Science.gov (United States)

    Beery, Joshua A; Day, Jennifer E

    2015-03-03

    Wind energy development is an increasingly popular form of renewable energy infrastructure in rural areas. Communities generally perceive socioeconomic benefits accrue and that community funding structures are preferable to corporate structures, yet lack supporting quantitative data to inform energy policy. This study uses the Everpower wind development, to be located in Midwestern Ohio, as a hypothetical modeling environment to identify and examine socioeconomic impact trends arising from corporate, community and diversified funding structures. Analysis of five National Renewable Energy Laboratory Jobs and Economic Development Impact models incorporating local economic data and review of relevant literature were conducted. The findings suggest that community and diversified funding structures exhibit 40-100% higher socioeconomic impact levels than corporate structures. Prioritization of funding sources and retention of federal tax incentives were identified as key elements. The incorporation of local shares was found to mitigate the negative effects of foreign private equity, local debt financing increased economic output and opportunities for private equity investment were identified. The results provide the groundwork for energy policies focused to maximize socioeconomic impacts while creating opportunities for inclusive economic participation and improved social acceptance levels fundamental to the deployment of renewable energy technology.

  6. Wake Expansion Models

    DEFF Research Database (Denmark)

    Branlard, Emmanuel Simon Pierre

    2017-01-01

    Different models of wake expansion are presented in this chapter: the 1D momentum theory model, the cylinder analog model and Theodorsen’s model. Far wake models such as the ones from Frandsen or Rathmann or only briefly mentioned. The different models are compared to each other. Results from...

  7. Irregular sleep-wake syndrome

    Science.gov (United States)

    Sleep-wake syndrome - irregular; Circadian rhythm sleep disorder - irregular sleep-wake type ... have sleep disturbances on occasion. But if this type of irregular sleep-wake pattern occurs regularly and without cause, see your provider.

  8. Analysis of Power Enhancement for a Row of Wind Turbines Using the Actuator Line Technique

    International Nuclear Information System (INIS)

    Mikkelsen, Robert; Soerensen, Jens N; Oeye, Stig; Troldborg, Niels

    2007-01-01

    The effect of wake interaction for a row of three wind turbines in a wind farm is analysed using the actuator line technique. Both full wake and half wake situations are considered with the aim of deriving the optimal pitch setting of the foremost turbine, with respect to the total power from the row. The mutual distance between the turbines is 5 diameters and the turbines are considered to operate in a wind shear with an exponent of 0.15, with the rotor centre located at 1.4 radii from the ground. The main findings reveal clear effects of reducing the loading on the foremost turbine towards increased production of turbine 2 and 3 in a row

  9. Effect of Blade Roughness on Transition and Wind Turbine Performance.

    Energy Technology Data Exchange (ETDEWEB)

    Ehrmann, Robert S. [Texas A & M Univ., College Station, TX (United States); White, E. B. [Texas A & M Univ., College Station, TX (United States)

    2015-09-01

    The real-world effect of accumulated surface roughness on wind-turbine power production is not well understood. To isolate specific blade roughness features and test their effect, field measurements of turbine-blade roughness were made and simulated on a NACA 633-418 airfoil in a wind tunnel. Insect roughness, paint chips, and erosion were characterized then manufactured. In the tests, these roughness configurations were recreated as distributed roughness, a forward-facing step, and an eroded leading edge. Distributed roughness was tested in three heights and five densities. Chord Reynolds number was varied between 0:8 to 4:8 × 106. Measurements included lift, drag, pitching moment, and boundary-layer transition location. Results indicate minimal effect from paint-chip roughness. As distributed roughness height and density increase, the lift-curve slope, maximum lift, and lift-to-drag ratio decrease. As Reynolds number increases, natural transition is replaced by bypass transition. The critical roughness Reynolds number varies between 178 to 318, within the historical range. At a chord Reynolds number of 3:2 × 106, the maximum lift-to-drag ratio decreases 40% for 140 μm roughness, corresponding to a 2.3% loss in annual energy production. Simulated performance loss compares well to measured performance loss of an in-service wind turbine.

  10. Challenges in wind farm optimization

    DEFF Research Database (Denmark)

    Larsen, Gunner Chr.

    for the wind turbine modeling, where aeroelastic models are required, and for the wind farm flow field description, where in-stationary flow field modeling is needed to capture the complicated mixture of atmospheric boundary layer (ABL) flows and upstream emitted meandering wind turbine wakes, which together...... dictates the fatigue loading of the individual wind turbines. Within an optimization context, the basic challenge in describing the in-stationary wind farm flow field is computational speed. The Dynamic Wake Meandering (DWM) model includes the basic features of a CFD Large Eddy Simulation approach...

  11. The effect of 40 hours of constant wakefulness on number comparison performance

    NARCIS (Netherlands)

    Steinborn, Michael B.; Bratzke, Daniel; Rolke, Bettina; Gordijn, Marijke C. M.; Beersma, Domien G. M.; Ulrich, Rolf

    2010-01-01

    We investigated the effects of sleep loss and circadian rhythm on number comparison performance. Magnitude comparison of single-digits is robustly characterized by a distance effect: Close numbers (e.g., 5 versus 6) produce longer reaction times than numbers further apart (e.g., 2 versus 8). This

  12. Wind Farms’ Spatial Distribution Effect on Power System Reserves Requirements

    DEFF Research Database (Denmark)

    Sørensen, Poul Ejnar; Cutululis, Nicolaos Antonio

    2010-01-01

    The wind power development during last millennium was typically based on small wind turbines dispersed over large areas, leading to a significant smoothing of the wind power fluctuations in a power system balancing area. The present development goes towards much larger wind farms, concentrated...... in smaller areas, which causes the total wind power fluctuations in power system areas to increase significantly. The impact of future large wind farms spatial distribution with respect to the power system reserve requirements is analyzed in this paper. For this purpose, Correlated Wind (CorWind) power time...... series simulation model developed to simulate wind power variability over a large area is used. As a study case, two scenarios for short term offshore wind power development in the West Danish power system region are used. The first scenario assumes that all the wind farms are built in the region...

  13. Simulating effects of a wind-turbine array using LES and RANS: Simulating turbines using LES and RANS

    Energy Technology Data Exchange (ETDEWEB)

    Vanderwende, Brian J. [Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder Colorado USA; Now at National Center for Atmospheric Research, Boulder Colorado USA; Kosović, Branko [National Center for Atmospheric Research, Boulder Colorado USA; Lundquist, Julie K. [Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder Colorado USA; National Renewable Energy Laboratory, Golden Colorado USA; Mirocha, Jeffrey D. [Lawrence Livermore National Laboratory, Livermore California USA

    2016-08-27

    Growth in wind power production has motivated investigation of wind-farm impacts on in situ flow fields and downstream interactions with agriculture and other wind farms. These impacts can be simulated with both large-eddy simulations (LES) and mesoscale wind-farm parameterizations (WFP). The Weather Research and Forecasting (WRF) model offers both approaches. We used the validated generalized actuator disk (GAD) parameterization in WRF-LES to assess WFP performance. A 12-turbine array was simulated using the GAD model and the WFP in WRF. We examined the performance of each scheme in both convective and stable conditions. The GAD model and WFP produced qualitatively similar wind speed deficits and turbulent kinetic energy (TKE) production across the array in both stability regimes, though the magnitudes of velocity deficits and TKE production levels were underestimated and overestimated, respectively. While wake growth slowed in the latter half of the WFP array as expected, wakes did not approach steady state by the end of the array as simulated by the GAD model. A sensitivity test involving the deactivation of explicit TKE production by the WFP resulted in turbulence levels within the array well that were below those produced by the GAD in both stable and unstable conditions. Finally, the WFP overestimated downwind power production deficits in stable conditions because of the lack of wake stabilization in the latter half of the array.

  14. Armodafinil, the R-enantiomer of modafinil: wake-promoting effects and pharmacokinetic profile in the rat.

    Science.gov (United States)

    Wisor, Jonathan P; Dement, William C; Aimone, Lisa; Williams, Michael; Bozyczko-Coyne, Donna

    2006-11-01

    Modafinil reduces the excessive sleepiness associated with narcolepsy, obstructive sleep apnea/hypopnea syndrome, and shift work sleep disorder. In rats, modafinil promotes dose-dependent increases in wake duration. The wake-promoting activity of the R-enantiomer of modafinil (armodafinil) was evaluated in WKY rats and compared to the classical stimulant, D-methamphetamine. Electroencephalographic and electromyographic signals were assessed via a tethered cranial implant. Body temperature and locomotor activity were assessed by telemetry via intraperitoneal implant. Rats (n=60, 12 per group) were subjected to one of five parallel treatments: armodafinil at 30, 100 and 300 mg/kg i.p.; D-methamphetamine, 1 mg/kg i.p. and vehicle. Armodafinil and D-methamphetamine increased time spent awake relative to vehicle. Armodafinil-evoked increases in wake duration were dose-dependent and proportional to plasma compound exposure. Induction of wakefulness by D-methamphetamine was associated with an approximately two-fold increase in locomotor activity during the 2-h period immediately following administration relative to vehicle. D-methamphetamine also increased body temperature over the same time interval. The dose of armodafinil (100 mg/kg, i.p.) that was closest to D-methamphetamine in its wake-promoting efficacy did not produce changes in either body temperature or the intensity of locomotor activity relative to vehicle. Acute rebound hypersomnolence, characterized by increases in non-rapid eye movement sleep (NREMS) as a percentage of time and NREMS bout duration and by a decreased frequency of brief awakenings following sleep deprivation, occurred following D-methamphetamine-but not armodafinil-induced wake in this rat model which has been shown to be predictive of human drug responses.

  15. Jovian Plasmas Torus Interaction with Europa. Plasma Wake Structure and Effect of Inductive Magnetic Field: 3D Hybrid Kinetic Simulation

    Science.gov (United States)

    Lipatov, A. S.; Cooper, J F.; Paterson, W. R.; Sittler, E. C., Jr.; Hartle, R. E.; Simpson, David G.

    2013-01-01

    The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon-magnetosphere system with respect to a variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo Orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa (Cassidy et al., 2007; Shematovich et al., 2005). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider the models with Oþ þ and Sþ þ background plasma, and various betas for background ions and electrons, and pickup electrons. The majority of O2 atmosphere is thermal with an extended non-thermal population (Cassidy et al., 2007). In this paper, we discuss two tasks: (1) the plasma wake structure dependence on the parameters of the upstream plasma and Europa's atmosphere (model I, cases (a) and (b) with a homogeneous Jovian magnetosphere field, an inductive magnetic dipole and high oceanic shell conductivity); and (2) estimation of the possible effect of an induced magnetic field arising from oceanic shell conductivity. This effect was estimated based on the difference between the observed and modeled magnetic fields (model II, case (c) with an inhomogeneous Jovian magnetosphere field, an inductive

  16. Effects of wind application on thermal perception and self-paced performance

    NARCIS (Netherlands)

    Teunissen, L.P.J.; Haan, A. de; Koning, J.J. de; Daanen, H.A.M.

    2013-01-01

    Physiological and perceptual effects of wind cooling are often intertwined and have scarcely been studied in self-paced exercise. Therefore, we aimed to investigate (1) the independent perceptual effect of wind cooling and its impact on performance and (2) the responses to temporary wind cooling

  17. MHD effects of the solar wind flow around planets

    Directory of Open Access Journals (Sweden)

    H. K. Biernat

    2000-01-01

    Full Text Available The study of the interaction of the solar wind with magnetized and unmagnetized planets forms a central topic of space research. Focussing on planetary magnetosheaths, we review some major developments in this field. Magnetosheath structures depend crucially on the orientation of the interplanetary magnetic field, the solar wind Alfvén Mach number, the shape of the obstacle (axisymmetric/non-axisymmetric, etc., the boundary conditions at the magnetopause (low/high magnetic shear, and the degree of thermal anisotropy of the plasma. We illustrate the cases of Earth, Jupiter and Venus. The terrestrial magnetosphere is axisymmetric and has been probed in-situ by many spacecraft. Jupiter's magnetosphere is highly non-axisymmetric. Furthermore, we study magnetohydrodynamic effects in the Venus magnetosheath.

  18. Near wake features of a flying European Starling

    Science.gov (United States)

    Kirchhefer, Adam; Kopp, Gregory; Gurka, Roi

    2013-11-01

    A great deal of research focusing on flapping wings has been motivated by their high performance capabilities, especially in low Reynolds number configurations where static wing performance typically suffers. The approaches to studying flapping wings have taken different forms. One form has been the systematic investigation of the parameters that influence the relationship between flapping wings and their wake. The other form, and the approach used in the present work, is the investigation of flapping wings in nature. While the earliest work on the flapping wings of animals consists of observations of bird flight by Leonardo DaVinci, advances in technology have allowed for quantitative measurements of the wake. The near wake of a freely flying European starling has been measured using high speed, time-resolved, particle image velocimetry, simultaneously with high speed cameras which imaged the bird. These have been used to measure the near wake two-dimensional velocity field that can be associated with the bird's location and wing configuration in an avian wind tunnel. Time series of the velocities have been expressed as composite wake plots, which depict segments of the wing beat cycle for various spanwise locations in the wake. Measurements indicate that downwash is not produced during the upstroke, suggesting that the upstroke does not generate lift. As well, the wake velocities imply the presence of streamwise vortical structures, in addition to tip vortices. These two characteristics indicate similarities between the wake of a bird and the wake of a bat.

  19. Wind power

    International Nuclear Information System (INIS)

    Gipe, P.

    2007-01-01

    This book is a translation of the edition published in the USA under the title of ''wind power: renewable energy for home, farm and business''. In the wake of mass blackouts and energy crises, wind power remains a largely untapped resource of renewable energy. It is a booming worldwide industry whose technology, under the collective wing of aficionados like author Paul Gipe, is coming of age. Wind Power guides us through the emergent, sometimes daunting discourse on wind technology, giving frank explanations of how to use wind technology wisely and sound advice on how to avoid common mistakes. Since the mid-1970's, Paul Gipe has played a part in nearly every aspect of wind energy development from installing small turbines to promoting wind energy worldwide. As an American proponent of renewable energy, Gipe has earned the acclaim and respect of European energy specialists for years, but his arguments have often fallen on deaf ears at home. Today, the topic of wind power is cropping up everywhere from the beaches of Cape Cod to the Oregon-Washington border, and one wind turbine is capable of producing enough electricity per year to run 200 average American households. Now, Paul Gipe is back to shed light on this increasingly important energy source with a revised edition of Wind Power. Over the course of his career, Paul Gipe has been a proponent, participant, observer, and critic of the wind industry. His experience with wind has given rise to two previous books on the subject, Wind Energy Basics and Wind Power for Home and Business, which have sold over 50,000 copies. Wind Power for Home and Business has become a staple for both homeowners and professionals interested in the subject, and now, with energy prices soaring, interest in wind power is hitting an all-time high. With chapters on output and economics, Wind Power discloses how much you can expect from each method of wind technology, both in terms of energy and financial savings. The book updated models

  20. Differential effects of wake promoting drug Modafinil in aversive learning paradigms

    Directory of Open Access Journals (Sweden)

    Bharanidharan eShanmugasundaram

    2015-08-01

    Full Text Available Modafinil (MO an inhibitor of the dopamine transporter was initially approved to treat narcolepsy, a sleep related disorder in humans. One interesting side-effect of this drug, which emerged from preclinical and clinical studies, is the facilitation of cognitive performance. So far, this was primarily shown in appetitive learning paradigms, but it is yet unclear whether MO exerts a more general cognitive enhancement effect. Thus, the aim of the present study in rats was to extend these findings by testing the effects of MO in two aversive paradigms, Pavlovian fear conditioning (FC and the operant two-way active avoidance (TWA learning paradigms. We discovered a differential, task-dependent effect of MO. In the FC paradigm MO treated rats showed a dose-dependent enhancement of fear memory compared to vehicle treated rats, indicated by increased context-related freezing. Cue related fear memory remained unaffected. In the TWA paradigm MO induced a slight, but significant decrease of avoidance responses compared to vehicle treated animals, while the number of escape reactions during the acquisition of the TWA task remained unaffected. These findings expand the knowledge in the regulation of cognitive abilities and may contribute to the understanding of the contraindicative effects of MO in anxiety related mental disorders.