| 1. |
- Muhle, Franz, et al.
(författare)
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Blind test comparison on the wake behind a yawed wind turbine
- 2018
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Ingår i: Wind Energy Science. - : COPERNICUS GESELLSCHAFT MBH. - 2366-7443 .- 2366-7451. ; 3:2, s. 883-903
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Tidskriftsartikel (refereegranskat)abstract
- This article summarizes the results of the "Blind test 5" workshop, which was held in Visby, Sweden, in May 2017. This study compares the numerical predictions of the wake flow behind a model wind turbine operated in yaw to experimental wind tunnel results. Prior to the workshop, research groups were invited to predict the turbine performance and wake flow properties using computational fluid dynamics (CFD) methods. For this purpose, the power, thrust, and yaw moments for a 30 degrees yawed model turbine, as well as the wake's mean and turbulent streamwise and vertical flow components, were measured in the wind tunnel at the Norwegian University of Science and Technology (NTNU). In order to increase the complexity, a non-yawed downstream turbine was added in a second test case, while a third test case challenged the modelers with a new rotor and turbine geometry. Four participants submitted predictions using different flow solvers, three of which were based on large eddy simulations (LES) while another one used an improved delayed detached eddy simulation (IDDES) model. The performance of a single yawed turbine was fairly well predicted by all simulations, both in the first and third test cases. The scatter in the downstream turbine performance predictions in the second test case, however, was found to be significantly larger. The complex asymmetric shape of the mean streamwise and vertical velocities was generally well predicted by all the simulations for all test cases. The largest improvement with respect to previous blind tests is the good prediction of the levels of TKE in the wake, even for the complex case of yaw misalignment. These very promising results confirm the mature development stage of LES/DES simulations for wind turbine wake modeling, while competitive advantages might be obtained by faster computational methods.
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| 2. |
- Vikström, Kevin, et al.
(författare)
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High influence of baseline respiration in a sub-Arctic coastal ecosystem
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Respiration is a key metabolic process in the marine environment that is usually assumed to be driven by phytoplankton production. However, respiration in the absence of contemporary phytoplankton production, termed baseline respiration, can influence the energetics of an ecosystem and its sensitivity to hypoxia. Direct studies of baseline respiration and its importance for coastal oxygen status are currently lacking. This study aims to obtain a first estimate of baseline respiration in a sub-arctic estuary, determine its contribution to annual plankton community respiration and identify the main carbon sources. The four different methods used to define baseline respiration converged on an average rate of 4.2 mmol O2 m-3 d-1 ± 0.1 (SE), corresponding to an annual contribution of 50 % of planktonic respiration on the basin scale. Respiration during the winter season (sporadic ice cover) was significant and comprised 25 % of annual pelagic respiration. No correlation between plankton respiration and phytoplankton production occurred on the intra-annual scale, while there was a weak exponential dependence on riverine total organic carbon inflow combined with phytoplankton production (i.e., major C input). Measured carbon sources could supply most (78 %) of the annual plankton respiration but only 39 % of the winter season respiration, suggesting some missing carbon sources. Nitrification had a negligible (≤ 2.4 %) effect on baseline respiration in the system. The results showed that baseline respiration could constitute a significant share of coastal plankton respiration, when allochthonous carbon sources dominate the carbon supply.
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| 3. |
- Vikström, Kevin, 1988-, et al.
(författare)
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Strong Influence of Baseline Respiration in an Oligotrophic Coastal Ecosystem
- 2020
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Ingår i: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Respiration is a key metabolic process in the marine environment and contemporary phytoplankton production (PhP) is commonly assumed the main driver. However, respiration in the absence of contemporary PhP, termed baseline respiration, can influence the energetics of an ecosystem and its sensitivity to hypoxia. Direct studies of baseline respiration are currently lacking. This study aims to obtain a first estimate of baseline respiration in a sub-arctic estuary and determine its contribution to plankton community respiration. Three approaches used to define baseline respiration determined the average rate to be 4.1 ± 0.1 (SE) mmol O2 m–3 d–1. A hypsographic model at the basin scale accounting for seasonal variation estimated an annual contribution of 30% baseline respiration to planktonic respiration. There was no correlation between plankton respiration and PhP, but a significant linear dependence was found with the total carbon supply from phytoplankton and riverine input. The sum of dissolved organic carbon transported by rivers, provided by both benthic and pelagic algae, could sustain 69% of the annual plankton respiration, of which as much as 25% occurred during winter. However, only 32% of the winter season respiration was explained, indicating that unknown carbon sources exist during the winter. Nitrification had a negligible (≤2.4%) effect on baseline respiration in the system. The results show that baseline respiration accounted for a significant percentage of coastal plankton respiration when allochthonous sources dominated the carbon supply, weakening the respiration-to- PhP relationship.
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