Near-ground turbulence of the Bora wind in summertime

Lepri, Petra; Večenaj, Željko; Kozmar, Hrvoje; Grisogono, Branko

doi:10.1016/j.jweia.2015.09.013

Cited by 12 publications

(13 citation statements)

References 34 publications

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“…Recently, microscale properties of Bora have been investigated for different Bora types [20], confirming most of previous results related to Bora periodicity and turbulence properties [21,22]. Bora turbulence properties were studied in [23,24] as well, with a particular focus on turbulence intensity, Reynolds shear stress, and turbulence length scales. Research at specific regions in Croatia (Pometeno brdo near Split [22] and Maslenica [20]), revealed that the near-ground wind speed profile of Bora is in good agreement with the logarithmic law and power law description, which are commonly used in wind engineering.…”

Section: Introductionsupporting

confidence: 71%

Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia

et al. 2019

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Southwest Slovenia is a region well-known for frequent episodes of strong and gusty Bora wind, which may damage structures, affect traffic, and poses threats to human safety in general. With the increased availability of computational power, the interest in high resolution modeling of Bora on local scales is growing. To model it adequately, the flow characteristics of Bora should be experimentally investigated and parameterized. This study presents the analysis of wind speed vertical profiles at Razdrto, Slovenia, a location strongly exposed to Bora during six Bora episodes of different duration, appearing between April 2010 and May 2011. The empirical power law and the logarithmic law for Bora wind, commonly used for the description of neutrally stratified atmosphere, were evaluated for 10-min averaged wind speed data measured at four different heights. Power law and logarithmic law wind speed profiles, which are commonly used in high resolution computational models, were found to approximate well the measured data. The obtained power law coefficient and logarithmic law parameters, which are for modeling purposes commonly taken to be constant for a specific site, were found to vary significantly between different Bora episodes, most notably due to different wind direction over complex terrain. To increase modeling precision, the effects of local topography on wind profile parameters needs to be experimentally assessed and implemented.

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Section: Introductionsupporting

confidence: 71%

Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia

et al. 2019

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“…The hill models were designed to closely represent realistic terrain conditions that commonly appear in the full-scale, e.g. Lepri et al [34], [35], rather than some generic shape. 16 TRANSACTIONS OF FAMENA XLIII-3 (2019) Each hill model is 600 mm long in the main flow direction (along the wind tunnel test section) and 1000 mm wide (lateral to the main flow direction).…”

Section: Methodsmentioning

confidence: 99%

Wind Characteristics in the Wake of a Non-Rotating Wind Turbine close to a Hill

Kozmar

Allori

Bartoli

et al. 2019

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Hilly terrain may considerably influence energy yield and structural loading of wind turbines. Wind energy developers are therefore required to accurately predict wind characteristics at the wind farm site already in the designing phase. It is necessary to determine how particular hill shape and size affect wind characteristics at the location of wind turbines operating in the wake of a hill. In order to address this complex issue, small-scale laboratory experiments were carried out in a boundary layer wind tunnel (BLWT). The focus was on characteristics of the flow at the same position downstream of the hill and the wind turbine models studied on various sizes and shapes of the hill model. Three hill models (a small and a large hill with laterally uniform heights and a hill with a bay) were exposed to the thermally neutrally stratified atmospheric boundary layer (ABL) simulation. In each experiment, there was only one hill model in the BLWT test section. The configuration without the hill, i.e. the flat terrain model, was tested as a reference case. Downstream of the hill model, there was a single (alone-standing) wind turbine model. Flow characteristics were studied downstream (behind) the wind turbine model. The wind turbine model was in the parking position in order to study wind characteristics in the situation with a strong wind when there is no rotation of rotor blades. The experimental results indicate a velocity decrease and stronger turbulence in the wind turbine wake in the presence of a hill, which trend is more pronounced in the case of larger hills. Strong velocity gradients are observed around the hub height in the large hill configuration, while this velocity deficit is the smallest in the hill with a bay configuration due to flow channeling. The velocity power spectra reveal the characteristic peak due to the vortex shedding from the hill ridge. The obtained results provide a new insight into the turbulent wake characteristics of a single wind turbine placed downstream of a hill with a potential to serve as a validation tool for computational studies.

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“…They also found that thermal stratification of the surface layer is near neutral due to strong mechanical mixing. Using the same data, Lepri et al [1,36] further investigated turbulence intensity, Reynolds shear stress and turbulence length scale profiles for the mentioned location.…”

Section: Introductionmentioning

confidence: 99%

Micro-Scale Properties of Different Bora Types

et al. 2018

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Abstract:In this paper we use 20 Hz wind measurements on three levels (2, 5, and 10 m) to investigate the differences in micro-scale properties of different bora types, i.e., deep and shallow bora with further subdivision to cyclonic and anticyclonic bora cases. Using Fourier spectral analysis, we investigate a suitable turbulence averaging scale and bora gust pulsations. The obtained data set is further used to test the Monin-Obukhov similarity theory, the surface layer stratification, the behavior of the terms in the prognostic turbulence kinetic energy equation, and the wind profiles. One of our main goals is to identify possible micro-scale differences between shallow and deep bora types because of the possible different mountain wave dynamics in those flows. We found that a turbulence averaging scale of 30 min is suitable for this location and is in agreement with previous bora studies. The wind speed power spectral densities of all selected bora episodes showed pulsations with periods of 2-8 min. This suggests that mountain wave breaking was present in all cases, regardless of flow depth and synoptic type. The stability parameter analysis confirmed the near-neutral thermal stratification of bora; a consequence of intensive mechanical mixing. No significant differences related to bora type were observed in other micro-scale parameters.

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Near-ground turbulence of the Bora wind in summertime

Cited by 12 publications

References 34 publications

Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia

Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia

Wind Characteristics in the Wake of a Non-Rotating Wind Turbine close to a Hill

Micro-Scale Properties of Different Bora Types

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