| 1. |
- Andersen, Soren Juhl, et al.
(författare)
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Statistics of LES Simulations of Large Wind Farms
- 2016
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Ingår i: SCIENCE OF MAKING TORQUE FROM WIND (TORQUE 2016). - : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- Numerous large eddy simulations are performed of large wind farms using the actuator line method, which has been fully coupled to the aero-elastic code, Flex5. The higher order moments of the flow field inside large wind farms is examined in order to determine a representative reference velocity. The statistical moments appear to collapse and hence the turbulence inside large wind farms can potentially be scaled accordingly. The thrust coefficient is estimated by two different reference velocities and the generic C-T expression by Frandsen. A reference velocity derived from the power production is shown to give very good agreement and furthermore enables the very good estimation of the thrust force using only the steady C-T-curve, even for very short time samples. Finally, the effective turbulence inside large wind farms and the equivalent loads are examined.
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| 2. |
- Arnqvist, Johan, 1985-, et al.
(författare)
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Investigation of Turbulence Accuracy When Modeling Wind in Realistic Forests Using LES
- 2019
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Ingår i: Progress In Turbulence Viii. - Cham : SPRINGER INTERNATIONAL PUBLISHING AG. - 9783030221966 - 9783030221959 ; , s. 291-296
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Konferensbidrag (refereegranskat)abstract
- This study presents an evaluation of wind field simulations, in neutral atmospheric conditions, above a heterogeneous forest. The calculations were performed with Large-Eddy Simulation (LES) code OpenFOAM, with explicit modelling of the forest through drag coefficient and forest density. The findings indicate that a large modelling domain is needed in order to reproduce the measurements in different wind directions, since the effect of far upwind forest characteristics influence the wind and turbulence profiles. It is further shown that even though the low resolution of the LES simulations lead to slightly misrepresented single point turbulence characteristics, two point turbulence characteristics are well predicted due to spatial filtering of the small scales.
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| 3. |
- Asmuth, Henrik, et al.
(författare)
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Actuator line simulations of wind turbine wakes using the lattice Boltzmann method
- 2020
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Ingår i: Wind Energy Science. - : Copernicus GmbH. - 2366-7443 .- 2366-7451. ; 5:2, s. 623-645
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Tidskriftsartikel (refereegranskat)abstract
- The high computational demand of large-eddy simulations (LESs) remains the biggest obstacle for a wider applicability of the method in the field of wind energy. Recent progress of GPU-based (graphics processing unit) lattice Boltzmann frameworks provides significant performance gains alleviating such constraints. The presented work investigates the potential of LES of wind turbine wakes using the cumulant lattice Boltzmann method (CLBM). The wind turbine is represented by the actuator line model (ALM). The implementation is validated and discussed by means of a code-to-code comparison to an established finite-volume Navier–Stokes solver. To this end, the ALM is subjected to both laminar and turbulent inflow while a standard Smagorinsky sub-grid-scale model is employed in the two numerical approaches. The resulting wake characteristics are discussed in terms of the first- and second-order statistics as well the spectra of the turbulence kinetic energy. The near-wake characteristics in laminar inflow are shown to match closely with differences of less than 3 % in the wake deficit. Larger discrepancies are found in the far wake and relate to differences in the point of the laminar-turbulent transition of the wake. In line with other studies, these differences can be attributed to the different orders of accuracy of the two methods. Consistently better agreement is found in turbulent inflow due to the lower impact of the numerical scheme on the wake transition. In summary, the study outlines the feasibility of wind turbine simulations using the CLBM and further validates the presented set-up. Furthermore, it highlights the computational potential of GPU-based LBM implementations for wind energy applications. For the presented cases, near-real-time performance was achieved using a single, off-the-shelf GPU on a local workstation.
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| 4. |
- Asmuth, Henrik, et al.
(författare)
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Assessment of Weak Compressibility in Actuator Line Simulations of Wind Turbine Wakes
- 2020
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1618
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Tidskriftsartikel (refereegranskat)abstract
- The trend of increasing rotor diameters and tip-speeds has brought about concerns of non-negligible compressibility effects in wind turbine aerodynamics. The investigation of such effects on wakes is particularly difficult when using actuator line models (ALM). This is because crucial regions of the flow, i.e. the direct vicinity of the blade, are not simulated but represented by body forces. To separately assess the impact of compressibility on the wake and the ALM itself, we conduct large-eddy simulations (LES) where the forces of the ALM are prescribed and based on the local sampled velocity (standard procedure), respectively. The LES are based on the weakly-compressible Lattice Boltzmann Method (LBM). Further to the comparison of (near-)incompressible to compressible simulations we investigate cases with artificially increased compressibility. This is commonly done in weakly-compressible approaches to reduce the computational demand. The investigation with prescribed forces shows that compressibility effects in the wake flow are negligible. Small differences in the wake velocity (of max. 1%) are found to be related to local compressibility effects in the direct vicinity of the ALM. Most significantly, compressibility is found to affect the sampled velocity and thereby accuracy of the ALM.
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| 5. |
- Asmuth, Henrik, et al.
(författare)
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How Fast is Fast Enough? : Industry Perspectives on the Use of Large-eddy Simulation in Wind Energy
- 2023
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Ingår i: WAKE CONFERENCE 2023. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- The use of graphics processing units (GPUs) has facilitated unprecedented performance gains for computational fluids dynamics in recent years. In many industries this has enabled the integration of large-eddy simulation (LES) in the engineering practice. Flow modelling in the wind industry though still primarily relies on models with significantly lower fidelity. This paper seeks to investigate the reasons why wind energy applications of LES are still an exception in the industrial practice. On that account, we present a survey among industry experts on the matter. The survey shows that the large runtimes and computational costs of LES are still seen as a main obstacle. However, other reasons such as a lack of expertise and user experience, the need for more validation, and lacking trust in the potential benefits of LES reveal that computational efficiency is not the only concern. Lastly, we present an exemplary simulation of a generic offshore wind farm using a GPU-resident Lattice Boltzmann LES framework. The example shows that the runtime requirements stated by a large part of the respondents can already now be fulfilled with reasonable hardware effort.
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| 6. |
- Asmuth, Henrik, et al.
(författare)
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The Actuator Line Model in Lattice Boltzmann Frameworks : Numerical Sensitivity and Computational Performance
- 2019
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1256
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Tidskriftsartikel (refereegranskat)abstract
- The growing use of large-eddy simulations for the modelling of wind farms makes the need for efficient numerical frameworks more essential than ever. GPU-accelerated implementations of the Lattice Boltzmann Method (LBM) have shown to provide significant performance gains over classical Navier-Stokes-based computational fluid dynamics. Yet, their use in the field of wind energy remains limited to date. In this fundamental study the cumulant LBM is scrutinised for actuator line simulations of wind turbines. The numerical sensitivity of the method in a simple uniform inflow is investigated with respect to spatial and temporal resolution as well as the width of the actuator line’s regularisation kernel. Comparable accuracy and slightly better stability properties are shown in relation to a standard Navier-Stokes implementation. The results indicate the overall suitability of the cumulant LBM for wind turbine wake simulations. The potential of the LBM for future wind energy applications is clarified by means of a brief comparison of computational performance.
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| 7. |
- Asmuth, Henrik, et al.
(författare)
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Wall-modeled lattice Boltzmann large-eddy simulation of neutral atmospheric boundary layers
- 2021
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Ingår i: Physics of fluids. - : American Institute of Physics (AIP). - 1070-6631 .- 1089-7666. ; 33:10, s. 105111-105111
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Tidskriftsartikel (refereegranskat)abstract
- The lattice Boltzmann method (LBM) sees a growing popularity in the field of atmospheric sciences and wind energy, largely due to itsexcellent computational performance. Still, LBM large-eddy simulation (LES) studies of canonical atmospheric boundary layer flows remainlimited. One reason for this is the early stage of development of LBM-specific wall models. In this work, we discuss LBM–LES of isothermalpressure-driven rough-wall boundary layers using a cumulant collision model. To that end, we also present a novel wall modeling approach,referred to as inverse momentum exchange method (iMEM). The iMEM enforces a wall shear stress at the off-wall grid points by adjustingthe slip velocity in bounce-back boundary schemes. In contrast to other methods, the approach does not rely on the eddy viscosity, nor doesit require the reconstruction of distribution functions. Initially, we investigate different aspects of the modeling of the wall shear stress, i.e.,an averaging of the input velocity as well as the wall-normal distance of its sampling location. Particularly, sampling locations above the firstoff-wall node are found to be an effective measure to reduce the occurring log-layer mismatch. Furthermore, we analyze the turbulence statis-tics at different grid resolutions. The results are compared to phenomenological scaling laws, experimental, and numerical references. Theanalysis demonstrates a satisfactory performance of the numerical model, specifically when compared to a well-established mixed pseudo-spectral finite difference (PSFD) solver. Generally, the study underlines the suitability of the LBM and particularly the cumulant LBM forcomputationally efficient LES of wall-modeled boundary layer flows.
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| 8. |
- Asmuth, Henrik, et al.
(författare)
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Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements
- 2022
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Ingår i: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 191, s. 868-887
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Tidskriftsartikel (refereegranskat)abstract
- Predicting the power and loads of wind turbines in waked inflow conditions still presents a major modelling challenge. It requires the accurate modelling of the atmospheric flow conditions, wakes of upstream turbines and the response of the turbine of interest. Rigorous validations of model frameworks against measurements of utility-scale wind turbines in such scenarios remain limited to date. In this study, six models of different fidelity are compared against measurements from the DanAero experiment. The two benchmark cases feature a full-wake and partial-wake scenario, respectively. The simulations are compared against local pressure forces and inflow velocities measured on several blade sections of the downstream turbine, as well as met mast measurements and standard SCADA data. Regardless of the model fidelity, reasonable agreements are found in terms of the wake characteristics and turbine response. For instance, the azimuth variation of the mean aerodynamic forces acting on the blade was captured with a mean relative error of 15–20%. While various model-specific deficiencies could be identified, the study highlights the need for further full-scale measurement campaigns with even more extensive instrumentation. Furthermore, it is concluded that validations should not be limited to integrated and/or time-averaged quantities that conceal characteristic spatial or temporal variations.
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| 9. |
- Barney, Andrew
(författare)
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Energy planning for islands : Guiding island energy transition and decision-making
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The importance and benefits of transitioning away from fossil fuel based energy systems is becoming ever clearer. The transition is especially crucial for geographic islands that typically have limited, or no, access to mainland energy networks. This limited access means that they must rely on costly, economically and environmentally, imported fossil fuels for energy production. This isolation and reliance on imported fuels makes islands particularly energy insecure, which is only expected to worsen because of climate change. At the same time, much of the current guidance and policy developed to help plan for islands’ energy transition is based on the conditions and circumstances present on the mainland or on energy planning that focuses primarily on technical or economic parameters. To plan for a smoother, more successful transition away from fossil fuel based energy production on islands, more data is needed about islanders themselves and their local circumstances as well as planning guidance flexible enough to fit the variable needs of island planners that goes beyond a techno-economic focus.In this PhD Thesis and in response to these transition issues, an energy planning platform, REACT-DECARB, has been developed to specifically address the needs of island energy planners. This platform seeks to be holistic in its approach to facilitate the island energy transition planning procedure by considering typical island characteristics and energy transition processes while also including key technical, social, environmental and economic dimensions and granting planners flexibility in how they incorporate them. Additionally, surveys and interviews with island residents are conducted to gain an understanding of islanders’ motivations, priorities and awareness in relation to energy and energy transition as well as to determine if these can be of guidance to island energy transition planners.The applications of the REACT-DECARB platform on geographic islands representing eight different countries from around the EU with varying populations, land areas and climates identified energy transition opportunities and obstacles specific to the islands where the platform was applied as well as to other islands seeking to transition their energy systems. Moreover, these applications of the planning platform demonstrated its ability to help island planners in the development of holistic energy transition paths. The platform takes island energy transition planning beyond a focus on techno-economics by including a wider range of planning dimensions allowing them to decide the methods best suited to their island’s needs. Further, the interactions with island residents demonstrated that their relationships to energy could be informative in the development of energy transition plans as well as likely being critical to their success. Islanders’ understandings, motivations, priorities and awareness were found to be not only directly useful in guiding planners during the designing of island energy transition plans but can also serve to inform planners in how best to educate local residents about and engage them in local energy transition projects. Ultimately, the work in this Thesis contributes to the efforts to make sure islands’, and islanders’, needs and perspectives are considered and included as a part of the wider energy transition.
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| 10. |
- Barney, Andrew
(författare)
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Integrated regional energy planning for islands : Development of a decision-aiding methodological framework and application
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Clear and inclusive planning guidance for island planners seeking transitions away from traditional fossil fuel based energy systems is currently needed. At present, the guidance from the scientific community has largely been provided piecemeal and with significant focus on the specifics of single islands and, more often than not, on proposed energy systems’ techno-economics. To address these gaps in applicability and encourage a more balanced energy project analysis the REACT-DECARB integrated energy planning and decision-aiding platform has been developed. REACT-DECARB seeks to work as a comprehensive planning platform for island energy transition and this thesis investigates the ability of the platform to provide the support to planners needed to facilitate their transition planning. To do so the core concepts, descriptions and applications of decision making as well as a number of energy planning tools are presented. The platform is then described and its individual steps are applied to eight geographic islands within the EU. These applications of the platform identified key opportunities for the islands, such as significant RES potential, while also finding potential obstacles, such as land use conflicts. Further, it highlighted the high economic cost of seeking full electricity autonomy and of using substantial battery capacities. The platform additionally identified the importance local preferences can potentially have on the ranking of future energy scenarios as well as the impact lifetime project environmental costs can have on overall system environmental impacts. In summation, the REACT-DECARB platform is found to be an effective tool in directing island energy decarbonisation efforts by guiding local energy planners in what should be included in their planning and how these key elements can be incorporated in the decisions made. Further, the platform is found to be flexible enough to be applied to more than the specific circumstances of a single island and allows planners to adjust their approaches to its different steps as needed and to better match their capabilities.
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