Turbulence characterization of downbursts using LES

Aboshosha, Haitham; Bitsuamlak, Girma; Damatty, Ashraf El

doi:10.1016/j.jweia.2014.10.020

Cited by 64 publications

(26 citation statements)

References 55 publications

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“…Equations (13) and (14) are consistent with field measurements carried out up to a limited height above ground level (nearly 50 m, with a dominant number of anemometers in the first 30 m) [13,35]. On the other hand, recent CFD simulations through LES [36] and wind tunnel tests using the impinging jet method [37] showed a dependence of the turbulence intensity over height that deserves further studies.…”

Section: Generalized Wind Fieldsupporting

confidence: 74%

Directional response of structures to thunderstorm outflows

2019

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Due to the combined effect of the background wind, the translation of the downburst and the radial nature of the downdraft after the touchdown, a peculiar characteristic of a thunderstorm outflow as detected by an anemometer or experienced by a structure is the potential variation of the flow direction. The study of the wind-excited response of structures has habitually neglected this issue because, dealing traditionally with synoptic events, their direction is endowed with a regular pattern. This paper proposes two families of methods to take into account directional changes in the evaluation of the windexcited response of structures. The first one generalizes the method usually applied to downbursts, which by its nature implicitly assumes a non-directional response. The second one is based on a new directional decomposition strategy of the wind speed that represents a generalization to thunderstorm outflows of what is historically done for synoptic events. The conceptual aspects involved in and the results provided by these methods are critically discussed and compared both to each other and with regard to the traditional non-directional structural analysis of thunderstorm outflows.

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Section: Generalized Wind Fieldsupporting

confidence: 74%

Directional response of structures to thunderstorm outflows

2019

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“…In recent years, the modeling of downburst wind fields with the help of large-eddy simulation (LES) has gained in interest. Studies have ranged from those relying on idealized simulations [23][24][25][26][27] to full-storm physics simulations [28,29]. The full-storm simulations have been shown to have the ability to produce realistic high-fidelity data for downburst winds; however, the complex interactions of the microphysics on the resulting simulated storm and wind field produce a convoluted structure, from which direct relationships between cause and effect are generally difficult to assess.…”

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confidence: 99%

On Wind Turbine Loads During Thunderstorm Downbursts in Contrasting Atmospheric Stability Regimes

Hawbecker

Basu

et al. 2019

Energies

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Severe winds produced by thunderstorm downbursts pose a serious risk to the structural integrity of wind turbines. However, guidelines for wind turbine design (such as the International Electrotechnical Commission Standard, IEC 61400-1) do not describe the key physical characteristics of such events realistically. In this study, a large-eddy simulation model is employed to generate several idealized downburst events during contrasting atmospheric stability conditions that range from convective through neutral to stable. Wind and turbulence fields generated from this dataset are then used as inflow for a 5-MW land-based wind turbine model; associated turbine loads are estimated and compared for the different inflow conditions. We first discuss time-varying characteristics of the turbine-scale flow fields during the downbursts; next, we investigate the relationship between the velocity time series and turbine loads as well as the influence and effectiveness of turbine control systems (for blade pitch and nacelle yaw). Finally, a statistical analysis is conducted to assess the distinct influences of the contrasting stability regimes on extreme and fatigue loads on the wind turbine.Energies 2019, 12, 2773 2 of 30 duration, with stochastically generated turbulence added on to a mean flow field. From the IEC standard, the extreme operating gust (EOG) is defined as:where U(z, t) represents the wind speed as a function of height, z, and time, t; U(z) is a power-law wind profile; U gust is the gust magnitude at hub height; and T is a specific time span for the gust function, taken to be 10.5 s. These mean wind fields derived from the analytical functions can be grossly different from what has been observed during downbursts [7]; they also may not accurately describe the strong vertical shear observed sometimes, and the associated non-stationary characteristics of the flow field. As well, the turbulence models employed are often for overly simplified cases with assumptions of near-neutral stability conditions that may not be justified. Due to these shortcomings, a series of earlier studies [8][9][10][11][12][13] were conducted to assess how downburst-related inflow fields (based on observational data but analytically derived [14]) could influence turbine loads. These studies highlighted the potential impacts of downbursts on a single wind turbine as well as on an entire wind farm or turbine array. They also emphasized the importance of improved models over the current IEC guidelines suggested for such events, when considering turbine design and control. In comparison with the turbine loads resulting from the IEC load cases for extreme coherent gust (ECG), extreme direction change (EDC), and extreme coherent gust with direction change (ECD), all believed to represent transient events such as downbursts, the turbine loads that were produced when driven by the data-based analytical models differed greatly. (In two cases, as found by Nguyen et al. [8], the analytical models predicted loads that were 86% larger than those based...

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“…carried out systematic comparisons between the results provided by the impinging jet model, the cooling sorce model and full-scale measurements. Aboshosha et al (2015) used LES to improve the simulation of turbulence.…”

Section: Cfd Simulationsmentioning

confidence: 99%

Mixed Climatology, Non-synoptic Phenomena and Downburst Wind Loading of Structures

Solari

2019

Lecture Notes in Civil Engineering

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In 1961 Davenport published a paper, considered by most the constitutive deed of Wind Engineering, where meteorology, micrometeorology, climatology, aerodynamics and structural dynamics were embedded into a homogeneous framework of the wind loading of structures. This scheme, known as the "Davenport chain" and referred to a synoptic-scale extra-tropical cyclone is so limpid and elegant as to become a sort of axiom. Between 1976 and 1978 Gomes and Vickery separated thunderstorm from non-thunderstorm winds, determined their extreme distributions and derived a mixed statistical model later extended to other phenomena; this study, a milestone in the emerging issue of mixed climatology, proved the impossibility of labelling a heterogeneous range of phenomena characterized by different velocity fields, frequencies, durations and extensions by the generic term "wind". Many of these phenomena occur in limited and well-known areas. Extra-tropical cyclones and thunderstorms affect the entire planet. This paper provides a state-of-the-art of this subject, with particular regard to the studies conducted at the University of Genova on thunderstorms.

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Turbulence characterization of downbursts using LES

Cited by 64 publications

References 55 publications

Directional response of structures to thunderstorm outflows

Directional response of structures to thunderstorm outflows

On Wind Turbine Loads During Thunderstorm Downbursts in Contrasting Atmospheric Stability Regimes

Mixed Climatology, Non-synoptic Phenomena and Downburst Wind Loading of Structures

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