On wind turbine loads during the evening transition period

Wind Energy ◽  
2019 ◽  
Vol 22 (10) ◽  
pp. 1288-1309 ◽  
Author(s):  
Nan‐You Lu ◽  
Sukanta Basu ◽  
Lance Manuel
Keyword(s):  
Wind Turbine ◽  
Transition Period ◽  
Evening Transition

scholarly journals Large Eddy Simulation of Wind Turbine Wakes during the Evening Transition Period

2020 ◽  
Vol 1618 ◽  
pp. 062004
Author(s):  
W. Chanprasert ◽  
R. N. Sharma ◽  
J. E. Cater ◽  
S. E. Norris
Keyword(s):  
Large Eddy Simulation ◽  
Wind Turbine ◽  
Transition Period ◽  
Evening Transition ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals Countergradient heat flux observations during the evening transition period

2014 ◽  
Vol 14 (17) ◽  
pp. 9077-9085 ◽  
Author(s):  
E. Blay-Carreras ◽  
E. R. Pardyjak ◽  
D. Pino ◽  
D. C. Alexander ◽  
F. Lohou ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Surface Layer ◽  
Transition Period ◽  
Potential Temperature ◽  
Sensible Heat Flux ◽  
Buoyancy Flux ◽  
Horizontal Shear ◽  
Evening Transition ◽  
Virtual Potential Temperature

Abstract. Gradient-based turbulence models generally assume that the buoyancy flux ceases to introduce heat into the surface layer of the atmospheric boundary layer in temporal consonance with the gradient of the local virtual potential temperature. Here, we hypothesize that during the evening transition a delay exists between the instant when the buoyancy flux goes to zero and the time when the local gradient of the virtual potential temperature indicates a sign change. This phenomenon is studied using a range of data collected over several intensive observational periods (IOPs) during the Boundary Layer Late Afternoon and Sunset Turbulence field campaign conducted in Lannemezan, France. The focus is mainly on the lower part of the surface layer using a tower instrumented with high-speed temperature and velocity sensors. The results from this work confirm and quantify a flux-gradient delay. Specifically, the observed values of the delay are ~ 30–80 min. The existence of the delay and its duration can be explained by considering the convective timescale and the competition of forces associated with the classical Rayleigh–Bénard problem. This combined theory predicts that the last eddy formed while the sensible heat flux changes sign during the evening transition should produce a delay. It appears that this last eddy is decelerated through the action of turbulent momentum and thermal diffusivities, and that the delay is related to the convective turnover timescale. Observations indicate that as horizontal shear becomes more important, the delay time apparently increases to values greater than the convective turnover timescale.

scholarly journals A Simulation Study on Risks to Wind Turbine Arrays from Thunderstorm Downbursts in Different Atmospheric Stability Conditions

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5407
Author(s):  
Nan-You Lu ◽  
Lance Manuel ◽  
Patrick Hawbecker ◽  
Sukanta Basu
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Transition Period ◽  
Atmospheric Stability ◽  
Bending Moment ◽  
Stability Conditions ◽  
Wind Fields ◽  
Worst Case ◽  
Large Eddy Simulation Model ◽  
Turbine Arrays

Thunderstorm downbursts have been reported to cause damage or failure to wind turbine arrays. We extend a large-eddy simulation model used in previous work to generate downburst-related inflow fields with a view toward defining correlated wind fields that all turbines in an array would experience together during a downburst. We are also interested in establishing what role contrasting atmospheric stability conditions can play on the structural demands on the turbines. This interest is because the evening transition period, when thunderstorms are most common, is also when there is generally acknowledged time-varying stability in the atmospheric boundary layer. Our results reveal that the structure of a downburst’s ring vortices and dissipation of its outflow play important roles in the separate inflow fields for turbines located at different parts of the array; these effects vary with stability. Interacting with the ambient winds, the outflow of a downburst is found to have greater impacts in an “average” sense on structural loads for turbines farther from the touchdown center in the stable cases. Worst-case analyses show that the largest extreme loads, although somewhat dependent on the specific structural load variable considered, depend on the location of the turbine and on the prevailing atmospheric stability. The results of our calculations show the highest simulated foreaft tower bending moment to be 85.4 MN-m, which occurs at a unit sited in the array farther from touchdown center of the downburst initiated in a stable boundary layer.

scholarly journals Observing and Simulating Wind-Turbine Wakes During the Evening Transition

2017 ◽  
Vol 164 (3) ◽  
pp. 449-474 ◽  
Author(s):  
Joseph C. Y. Lee ◽  
Julie K. Lundquist
Keyword(s):  
Wind Turbine ◽  
Evening Transition

scholarly journals Countergradient heat flux observations during the evening transition period

2014 ◽  
Vol 14 (6) ◽  
pp. 7711-7737 ◽  
Author(s):  
E. Blay-Carreras ◽  
E. R. Pardyjak ◽  
D. Pino ◽  
D. C. Alexander ◽  
F. Lohou ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Surface Layer ◽  
Time Scale ◽  
Transition Period ◽  
Potential Temperature ◽  
Buoyancy Flux ◽  
Horizontal Shear ◽  
Evening Transition ◽  
Virtual Potential Temperature

Abstract. Gradient-based turbulence models generally assume that the buoyancy flux ceases to introduce heat into the surface layer of the atmospheric boundary layer in temporal consonance with the gradient of the local virtual potential temperature. Here, we hypothesize that during the evening transition a delay exists between the instant when the buoyancy flux goes to zero and the time when the local gradient of the virtual potential temperature indicates a sign change. This phenomenon is studied using a range of data collected over several Intensive Observational Periods (IOPs) during the Boundary Layer Late Afternoon and Sunset Turbulence field campaign conducted in Lannemezan, France. The focus is mainly on the lower part of the surface layer using a tower instrumented with high-speed temperature and velocity sensors. The results from this work confirm and quantify a flux-gradient delay. Specifically, the observed values of the delay are ~30–80 min. The existence of the delay and its duration can be explained by considering the convective time scale and the competition of forces associated with the classical Rayleigh–Bénard problem. This combined theory predicts that the last eddy formed while the sensible heat flux changes sign during the evening transition should produce a delay. It appears that this last eddy is decelerated through the action of turbulent momentum and thermal diffusivities, and that the delay is related to the convective turn – over time – scale. Observations indicate that as horizontal shear becomes more important, the delay time apparently increases to values greater than the convective turnover time-scale.

Treatment Considerations for Adolescents Who Exhibit Cognitive/Communication Problems: A Neuroscience Perspective

2020 ◽  
Vol 5 (6) ◽  
pp. 1767-1775
Author(s):  
Martha S. Burns
Keyword(s):  
Social Communication ◽  
Transition Period ◽  
Clinical Intervention ◽  
Review Article ◽  
Sensitive Period ◽  
Clinical Implications ◽  
Evidence Based ◽  
Communication Problems ◽  
Treatment Considerations ◽  
Behavioral Growth

Purpose Adolescence is a period of substantial neurophysiological and behavioral growth, representing a second sensitive period of brain development. It is a psychological and social transition period between childhood and adulthood with many beneficial changes occurring, especially with respect to potential responsiveness to clinical intervention. However, adolescent behavioral complexities introduce clinical challenges as well. The purpose of this review article is to review the current neuroimaging research on neurophysiological changes observed during adolescence and the cognitive and social behavioral counterparts, with specific attention to the clinical implications. The review article will then summarize currently available intervention tools that can be utilized by speech-language pathologists working with this population. It will conclude with available evidence-based social-communication approaches that may be applicable as well as available evidence-based supplemental technological cognitive interventions that may be useful in working with adolescents who exhibit language and communication issues. Conclusion As a transition period between childhood and adulthood, adolescence represents a second sensitive period during which there is opportunity for clinically derived beneficial cognitive and communication growth.

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