| 1. |
- Atzori, Marco, 1992-, et al.
(författare)
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A new perspective on skin-friction contributions in adverse-pressure-gradient turbulent boundary layers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- For adverse-pressure-gradient turbulent boundary layers, the study of integral skin-friction contributions still poses significant challenges. Beyond questions related to the integration boundaries and the derivation procedure, which have been thoroughly investigated in the literature, an important issue is how different terms should be aggregated. The nature of these flows, which exhibit significant in-homogeneity in the streamwise direction, usually results in cancellation between several contributions with high absolute values. We propose a formulation of the identity derived by Fukagata, Iwamoto \& Kasagi (Phys. Fluids, vol. 14, 2002, pp. 73--76), which we obtained from the convective form of the governing equations. A new skin-friction contribution is defined, considering wall-tangential convection and pressure gradient together. This contribution is related to the evolution of the dynamic pressure in the mean flow. The results of the decomposition are examined for a broad range of pressure-gradient conditions and different flow-control strategies. We found that the new formulation of the identity allows to readily identify the different regimes of near-equilibrium conditions and approaching separation. It also provides a more effective description of control effects. A similar aggregation between convection and pressure-gradient terms is also possible for any other decomposition where in-homogeneity contributions are considered explicitly.
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| 2. |
- Atzori, Marco, et al.
(författare)
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A new perspective on skin-friction contributions in adverse-pressure-gradient turbulent boundary layers
- 2023
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Ingår i: International Journal of Heat and Fluid Flow. - : Elsevier BV. - 0142-727X .- 1879-2278. ; 101
-
Tidskriftsartikel (refereegranskat)abstract
- For adverse-pressure-gradient turbulent boundary layers, the study of integral skin-friction contributions still poses significant challenges. Beyond questions related to the integration boundaries and the derivation procedure, which have been thoroughly investigated in the literature, an important issue is how different terms should be aggregated. The nature of these flows, which exhibit significant in-homogeneity in the streamwise direction, usually results in cancellation between several contributions with high absolute values. We propose a formulation of the identity derived by Fukagata et al. (2002), which we obtained from the convective form of the governing equations. A new skin-friction contribution is defined, considering wall-tangential convection and pressure gradient together. This contribution is related to the evolution of the dynamic pressure in the mean flow. The results of the decomposition are examined for a broad range of pressure-gradient conditions and different flow-control strategies. We found that the new formulation of the identity allows to readily identify the different regimes of near-equilibrium conditions and approaching separation. It also provides a more effective description of control effects. A similar aggregation between convection and pressure-gradient terms is also possible for any other decomposition where in-homogeneity contributions are considered explicitly.
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| 3. |
- Atzori, Marco, et al.
(författare)
-
In-situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In-situ visualization on HPC systems allows us to analyze simulation results that would otherwise be impossible, given the size of the simulation data sets and offline post-processing execution time. We design and develop in-situ visualization with Paraview Catalyst in Nek5000, a massively parallel Fortran and C code for computational fluid dynamics applications. We perform strong scalability tests up to 2,048 cores on KTH's Beskow Cray XC40 supercomputer and assess in-situ visualization's impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in-situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ~21\% on 2,048 cores (the relative efficiency of Nek5000 without in-situ operations is ~99\%). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in-situ processing time between rank 0 and all other ranks. Better scaling and load-balancing in the parallel image composition would considerably improve the performance and scalability of Nek5000 with in-situ capabilities in large-scale simulation.
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| 4. |
- Atzori, Marco, 1992-, et al.
(författare)
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In situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst
- 2022
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Ingår i: Journal of Supercomputing. - : Springer. - 0920-8542 .- 1573-0484. ; 78:3, s. 3605-3620
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Tidskriftsartikel (refereegranskat)abstract
- In situ visualization on high-performance computing systems allows us to analyze simulation results that would otherwise be impossible, given the size of the simulation data sets and offline post-processing execution time. We develop an in situ adaptor for Paraview Catalyst and Nek5000, a massively parallel Fortran and C code for computational fluid dynamics. We perform a strong scalability test up to 2048 cores on KTH’s Beskow Cray XC40 supercomputer and assess in situ visualization’s impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ≈ 21 % on 2048 cores (the relative efficiency of Nek5000 without in situ operations is ≈ 99 %). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses the Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in situ processing time between rank 0 and all other ranks. In our case, better scaling and load-balancing in the parallel image composition would considerably improve the performance of Nek5000 with in situ capabilities. In general, the result of this study highlights the technical challenges posed by the integration of high-performance simulation codes and data-analysis libraries and their practical use in complex cases, even when efficient algorithms already exist for a certain application scenario.
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| 5. |
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| 6. |
- Mallor, Fermin, et al.
(författare)
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Bayesian Optimisation of blowing and suction for drag reduction on a transonic airfoil
- 2023
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Ingår i: Proceedings of the 14th ERCOFTAC Symp. on Engineering Turbulence Modelling and Measurements (ETMM14), Barcelona, Spain. ; , s. 837-842
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Wall-normal blowing and suction has shown to be a promising active control method for friction drag reduction. In this work, we exploit a Bayesian optimization framework based on Gaussian process regression to find a configuration of non-homogeneous wall-normal blowing and suction capable of improving the aerodynamic efficiency of an RAE2822 airfoil in transonic conditions. The RANS simulations are carried out with the open-source solver SU2. During the optimization process, three different scenarios are considered: only the drag is minimized, the drag and the power needed to drive the control system are included, and the actuation power with a specified compressor efficiency are used for the calculation of the efficiency increase. Even in the most realistic case considering the actuation power and efficiencies an increase in the overall efficiency of 1.15% is reached.
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| 7. |
- Mallor, Fermin, et al.
(författare)
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Bayesian Optimization of Wall-Normal Blowing and Suction-Based Flow Control of a NACA 4412 Wing Profile
- 2023
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Ingår i: Flow Turbulence and Combustion. - : Springer Nature. - 1386-6184 .- 1573-1987.
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Tidskriftsartikel (refereegranskat)abstract
- Active flow-control techniques have shown promise for achieving high levels of drag reduction. However, these techniques are often complex and involve multiple tunable parameters, making it challenging to optimize their efficiency. Here, we present a Bayesian optimization (BO) approach based on Gaussian process regression to optimize a wall-normal blowing and suction control scheme for a NACA 4412 wing profile at two angles of attack: 5 and 11∘, corresponding to cruise and high-lift scenarios, respectively. An automated framework is developed by linking the BO code to the CFD solver OpenFOAM. RANS simulations (validated against high-fidelity LES and experimental data) are used in order to evaluate the different flow cases. BO is shown to provide rapid convergence towards a global maximum, even when the complexity of the response function is increased by introducing a model for the cost of the flow control actuation. The importance of considering the actuation cost is highlighted: while some cases yield a net drag reduction (NDR), they may result in an overall power increase. Furthermore, optimizing for NDR or net power reduction (NPR) can lead to significantly different actuation strategies. Finally, by considering losses and efficiencies representative of real-world applications, still a significant NPR is achieved in the 11∘ case, while net power reduction is only marginally positive in the 5∘ case.
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| 8. |
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| 9. |
- Mallor, Fermin, et al.
(författare)
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Design and setup of a wing model in the Minimum-Turbulence-Level wind tunnel
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A reinforced fiber-glass model of a NACA 4412 wing profile is designed and set-up in the Minimum-Turbulence-Level (MTL) wind-tunnel facility at KTH Royal Institute of Technology (Sweden), aiming to complement the high-fidelity numerical work performed by our research group on the same airfoil, including direct numerical simulations (DNS) and large-eddy simulations (LES). The model has 65 pressure taps, and the set-up includes two mounting panels designed to allow for particle image velocimetry (PIV) and hot-wire anemometry (HWA) measurements of the boundary layer on the model (both to be performed in a future campaign). In this first experimental campaign pressure scans are carried out at four angles of attack of interest (0, 5, 10 and 12 degrees), and at four different Reynolds numbers based on chord length and inflow velocity (200,000, 400,000, 1,000,000 and 1,640,000). The experimental data is then compared with reference high-fidelity and k- SST RANS simulations. The preliminary results show an excellent agreement with the reference numerical data, specially at the moderate angles of attack.
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| 10. |
- Mallor, Fermin, et al.
(författare)
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Experimental characterization of the turbulent boundary layer around a NACA 4412 wing profile
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A comprehensive experimental characterization of the turbulent boundary layers developing around a NACA 4412 wing profile is carried out in the Minimum Turbulence Level (MTL) wind tunnel located at KTH Royal Institute of Technology. The campaign included collecting wall-pressure data via built-in pressure taps, capturing velocity signals in TBLs using hot-wire anemometry (HWA), and conducting direct skin-friction measurements with oil-film interferometry (OFI). The research spanned two chord-based Reynolds numbers (Rec = 4 × 105 and106) and four angles of attack (5◦, 8◦, 11◦ and 14◦), encompassing a broad spectrum of flow conditions, from mild to strong adverse-pressure gradients (APGs), including scenarios where the TBL detaches from the wing surface. This extensive dataset offers crucial insights into TBL behavior under varied flow conditions, particularly in the context of APGs. Key findings include the quasi-independence of pressure coefficient distributions from Reynolds number, which aids in distinguishing Reynolds number effects from those due to APGs. The study also reveals changes in TBL dynamics as separation approaches, with energy shifting from the inner to the outer region and the eventual transition to a free-shear flow state post-separation. Additionally, the research addresses the challenges of spatial-averaging effects in TBL measurements, proposing a skin-friction-independent measure for the level of attenuation based on the modified diagnostic-plot scaling. The findings and database resulting from this campaign may be of special relevance of the development and validation of turbulence models, especially in the context of aeronautical applications.
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| 11. |
- Mallor, Fermin, et al.
(författare)
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High-fidelity simulations of the flow around a NACA 4412 wing section at high angles of attack
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This study uses high-resolution large-eddy simulations (LES) to investigate the turbulent flow around a NACA 4412 wing profile at multiple Reynoldsnumbers based on chord length and free-stream velocity (Rec = 2×105, 4×105 and 106) and angles of attack (AoA= 5◦, 8◦, 11◦ and 14◦). The introduction of Adaptive Mesh Refinement (AMR) and non-conformal meshing into the spectral-element-method code Nek5000 enabled the simulations at higher AoAs by permitting the use of wider domains, allowing to capture the largest turbulent scales associated with flow separation. The results provide a detailed database - including integral quantities, velocity statistics and spectra - which may be used for the evaluation lower-fidelity turbulence models. Furthermore, closer inspection of specific turbulent-boundary-layer (TBL) profiles allows us to discern between pressure-gradient (PG) and Reynolds-numbers effects on TBLs,showing that Re balances the PG, by reducing the impact of PG on the flow. Lastly, we assess the influence of flow history on TBLs, showing that a consistent flow history over an extended length is needed for TBLs to exhibit comparable profiles and characteristics.
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| 12. |
- Mallor, Fermin, et al.
(författare)
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In-Situ Analysis of Backflow Events and Their Relation to Separation in Wings Through Well-Resolved LES
- 2024
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Ingår i: ERCOFTAC Series. - : Springer Science and Business Media B.V.. ; , s. 17-22
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Wall-bounded turbulent flows as those occurring in transportation (e.g. aviation) or industrial applications (e.g turbomachinery), are usually subjected to pressure gradients (PGs). The presence of such PGs affects greatly the development and physics of the turbulent boundary layer (TBL), making it an open research area. An important phenomena associated with the presence of strong adverse PGs (APGs) as appearing in wings, is the separation of the boundary layer, which can lead to stall.
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| 13. |
- Mallor, Fermin, et al.
(författare)
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Modal decomposition of flow fields and convective heat transfer maps : An application to wall-proximity square ribs
- 2019
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier. - 0894-1777 .- 1879-2286. ; , s. 517-527
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Tidskriftsartikel (refereegranskat)abstract
- In this work the modal decomposition of convective heat transfer distributions in turbulent flows is explored. The organization and thermal footprint of the turbulent flow features generated downstream of wall-proximity two-dimensional square ribs immersed in a turbulent boundary layer are investigated experimentally. This study employs modal decomposition to investigate whether this analysis can allow identifying which characteristics of the flow topology are responsible for the Nusselt-number augmentation, aiming to uncover the underlying physics of heat-transfer enhancement. Heat transfer and flow velocity measurements are performed at a Reynolds number (based on the free-stream velocity and rib side-length) equal to 4600. Square ribs are tested for two different gap spacings from the wall (0.25 and 0.5 ribs side-length) and in wall-attached configuration. A low-thermal-inertia heat transfer sensor coupled with high-repetition-rate Infrared (IR) thermography is designed to study the unsteady variation of the convective heat-transfer coefficient downstream of the obstacles. Flow-field measurements are performed with non-time-resolved Particle Image Velocimetry (PIV). A modal analysis with Proper Orthogonal Decomposition (POD) is applied to both convective heat-transfer maps and velocity-fields. The comparison of the Nusselt-number spatial modes of the clean turbulent boundary layer configuration and of the configurations with the ribs shows a variation of the spatial pattern associated with oscillations with strong spanwise coherence, opposed to the thin elongated streaks which dominate the convective heat transfer in the clean turbulent boundary layer. In configurations where the convective heat transfer is enhanced by coherent structures located close to the wall, similar eigenspectra are observed for both flow field and convective heat transfer modes. The results of the modal analysis support a picture of a direct relation between the coherence of near-wall flow features and heat-transfer augmentation, providing a statistical evidence for the fact that near-wall coherent eddies are extremely efficient in enhancing heat transfer.
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| 14. |
- Mallor, Fermin, et al.
(författare)
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Spatial averaging effects in adverse pressure gradient turbulent boundary layers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Thermal anemometry sensors for time-resolved velocity measurements average the measured signal over the length of their sensor, thereby attenuating fluctuations stemming from scales smaller than the wire length. Several compensation methods have emerged for wall turbulence, the most prominent ones relying on the small-scale universality in canonical flows or on the reconstruction based on two attenuated variance profiles obtained with sensors of different length. To extend these methods to non-canonical flows, the present work considers various adverse-pressure gradient (APG) turbulent boundary layer (TBL) flows in order to explore how the small-scale energy is affected in the inner and outer layer and how the two prominent correction methods perform as function of wall-distance, wire length and flow condition. Our findings show that the increased levels of small-scale energy in the inner, but also outer layer associated with APG TBLs reduces the applicability of empirical methods based on the universality of small-scale energy. On the other hand, a correction based on the relationship between the spanwise Taylor microscale and the two-point streamwise velocity correlation function, is able to correct the attenuated profiles of non-canonical cases. Combining the strength of both methods, a composite profile for the spanwise Taylor microscale is suggested, which then is used for the correction of probe-length attenuation effects across a multitude of flow conditions.
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| 15. |
- Mallor, Fermin, et al.
(författare)
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Tracking backflow events and flow separation in wings
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This study presents an in-depth analysis of backflow event dynamics within non-equilibrium turbulent boundary layers under strong adverse pressure gradients. Large Eddy Simulation (LES) of the flow around a NACA 4412 wing profile at a chord-based Reynolds number of 4×105 and two angles of attack (5 and 11 degrees) are carried out with the spectral-element code Nek5000. The research focuses on the identification and time-tracking of backflow events, their growth mechanisms, and their impact on mean flow separation. Directed Acyclic Graphs (DAGs) are constructed to map the interconnectivity of backflow events over the wing surface, providing a framework to describe their evolution.The study reveals that while most backflow events are small, disconnected and localized, a significant portion of events (around 20%) display significant growth due to their merging with other backflows—a phenomenon not extensively reported in canonical flow studies. The major contribution of this research is the discovery of a single dynamical process, encapsulated by a unique DAG, that characterizes both the separation and incipient flow separation. The importance of merging in the development of large-scale separated regions is highlighted, suggesting that the merging process is a critical factor in the flow separation mechanism. The findings offer potential applications in flow control, suggesting that mitigating the merging process of backflow events could be an effective strategy to delay or prevent flow separation. This insight opens new avenues for the development of flow control techniques aimed at improving aerodynamic efficiency and performance. Further investigations could yield significant advancements in active flow control systems, contributing to the optimized design of aerodynamic surfaces and energy-efficient aerodynamic operations.
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| 16. |
- Mallor, Fermin
(författare)
-
Wings, turbulent boundary layers and flow separation
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present doctoral thesis investigates the turbulent flow developing around wing sections, focusing on the impact of adverse-pressure-gradient (APG) conditions on turbulent boundary layers (TBLs) and the physics of flow separation. Both experimental and numerical methods are employed to generate high-fidelity data sets and provide an in-depth analysis of the flow.The first objective of this thesis is the development of a comprehensive database for the flow around a NACA 4412 wing profile. For this purpose, adaptive mesh refinement (AMR) is used together with the spectral-element method code Nek5000. With AMR, high-resolution Large Eddy Simulations (LES) are conducted at various Reynolds numbers (Rec = 2×105, 4×105 and 1×106) and angles of attack (AoA=5°, 8°, 11°, 14°), which were previously unattainable. The effect that strong APGs have on TBLs developing around a wing section is assessed through the collection of statistics and time series. The results demonstrate the influence of APG conditions on both the mean and variance profiles of velocity, and on the distribution and production of turbulence energy within the TBL. Additionally, the connection of APG TBLs with flow separation is explored through the development of an in-situ identification and tracking algorithm, tightly integrated into Nek5000. Our findings show that, in contrast to canonical flows, backflow events in TBLs under strong APGs extensively merge to form larger structures that grow exponentially in size, eventually leading to significant flow separation near the wing’s trailing edge.Furthermore, a wind-tunnel experimental campaign is conducted to validate and extend the numerical results. Pressure, wall-shear stress and velocity measurements were carried out in the MTL wind tunnel at KTH Royal Institute of Technology. The study also scrutinizes measurement methodologies for APG TBLs, examining uncertainties in skin-friction determination and the impact of hot-wire probe lengths on velocity variance profiles.Finally, a study based on Reynolds-averaged Navier–Stokes (RANS) simulations, utilizing high-fidelity data for validation, is performed to assess the optimization of flow-control schemes based on blowing and suction. This study, later extended to a transonic airfoil, showcases Bayesian optimization (BO) as an efficient method for computational fluid dynamics (CFD)-based optimization problems.
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| 17. |
- Rosenberg, Emelie, et al.
(författare)
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Sentiment analysis on Twitter data towards climate action
- 2023
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Ingår i: Results in Engineering (RINENG). - : Elsevier BV. - 2590-1230. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the progress of the Sustainable Development Goals (SDGs) proposed by the United Nations (UN) is important, but difficult. In particular, policymakers would need to understand the sentiment within the public regarding challenges associated with climate change. With this in mind and the rise of social media, this work focuses on the task of uncovering the sentiment of Twitter users concerning climate-related issues. This is done by applying modern natural-language-processing (NLP) methods, i.e. VADER, TextBlob, and BERT, to estimate the sentiment of a gathered dataset based on climate-change keywords. A transfer-learning-based model applied to a pre-trained BERT model for embedding and tokenizing with logistic regression for sentiment classification outperformed the rule-based methods VADER and TextBlob; based on our analysis, the proposed approach led to the highest accuracy: 69%. The collected data contained significant noise, especially from the keyword 'energy'. Consequently, using more specific keywords would improve the results. The use of other methods, like BERTweet, would also increase the accuracy of the model. The overall sentiment in the analyzed data was positive. The distribution of the positive, neutral, and negative sentiments was very similar in the different SDGs.
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| 18. |
- Sanchez-Roncero, Alejandro, et al.
(författare)
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The Sustainable Development Goals and Aerospace Engineering : A critical note through Artificial Intelligence
- 2023
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Ingår i: Results in Engineering (RINENG). - : Elsevier BV. - 2590-1230. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- The 2030 Agenda of the United Nations (UN) revolves around the Sustainable Development Goals (SDGs). A critical step towards that objective is identifying whether scientific production aligns with the SDGs' achievement. To assess this, funders and research managers need to manually estimate the impact of their funding agenda on the SDGs, focusing on accuracy, scalability, and objectiveness. With this objective in mind, in this work, we develop ASDG, an easy-to-use Artificial-Intelligence-based model for automatically identifying the potential impact of scientific papers on the UN SDGs. As a demonstrator of ASDG, we analyze the alignment of recent aerospace publications with the SDGs. The Aerospace data set analyzed in this paper consists of approximately 820,000 papers published in English from 2011 to 2020 and indexed in the Scopus database. The most-contributed SDGs are 7 (on clean energy), 9 (on industry), 11 (on sustainable cities), and 13 (on climate action). The establishment of the SDGs by the UN in the middle of the 2010 decade did not significantly affect the data. However, we find clear discrepancies among countries, likely indicative of different priorities. Also, different trends can be seen in the most and least cited papers, with apparent differences in some SDGs. Finally, the number of abstracts the code cannot identify decreases with time, possibly showing the scientific community's awareness of SDG.
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| 19. |
- Sirmacek, B., et al.
(författare)
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The Potential of Artificial Intelligence for Achieving Healthy and Sustainable Societies
- 2023
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Ingår i: The Ethics of Artificial Intelligence for the Sustainable Development Goals. - : Springer Nature. ; , s. 65-96
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter we extend earlier work (Vinuesa et al., Nat Commun 11, 2020) on the potential of artificial intelligence (AI) to achieve the 17 Sustainable Development Goals (SDGs) proposed by the United Nations (UN) for the 2030 Agenda. The present contribution focuses on three SDGs related to healthy and sustainable societies, i.e., SDG 3 (on good health), SDG 11 (on sustainable cities), and SDG 13 (on climate action). This chapter extends the previous study within those three goals and goes beyond the 2030 targets. These SDGs are selected because they are closely related to the coronavirus disease 19 (COVID-19) pandemic and also to crises like climate change, which constitute important challenges to our society.
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| 20. |
- Tabatabaei, Narges, et al.
(författare)
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RANS Modelling of a NACA4412 Wake Using Wind Tunnel Measurements
- 2022
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Ingår i: Fluids. - : MDPI AG. - 2311-5521. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- Wake analysis plays a significant role in wind-farm planning through the evaluation of losses and energy yield. Wind-tunnel tests for wake studies have high costs and are time-consuming. Therefore, computational fluid dynamics (CFD) emerges as an efficient alternative. An especially attractive approach is based on the solution of the Reynolds-averaged Navier-Stokes (RANS) equations with two-equation turbulence closure models. The validity of this approach and its inherent limitations, however, remain to be fully understood. To this end, detailed wind-tunnel experiments in the wake of a NACA4412 wing section profile are compared with CFD results. Two- and three-dimensional RANS simulations are carried out for a range of angles of attack up to stall conditions at a chord- and inflow-based Reynolds number of Re-c = 4 x 10(5). Here, we aim to investigate the wake characteristics and self-similar behaviour, both from the experimental and numerical perspectives. The measurements are carried out by means of hot-wire anemometry capturing the wake pattern in several planes. The sensitivity of the CFD model to different configurations of the setup and the considerations required for reliable simulation are discussed. The agreement between CFD, experiments, and the literature is fairly good in many aspects, including the self-similar behaviour and wake parameters, as well as the flow field. Comparison of experiments with URANS/RANS data indicates that the latter is an adequate methodology to characterize wings and their wakes once the CFD setup is designed appropriately and the limitations due to discretization and turbulence modelling are considered.
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| 21. |
- Tanarro, Alvaro, et al.
(författare)
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Enabling adaptive mesh refinement for spectral-element simulations of turbulence around wing sections
- 2020
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Ingår i: Flow Turbulence and Combustion. - : Springer Nature. - 1386-6184 .- 1573-1987. ; 105:2, s. 415-436
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The implementation of adaptive mesh refinement (AMR) in the spectral-element method code Nek5000 is used for the first time on the well-resolved large-eddy simulation (LES) of the turbulent flow over wings. In particular, the flow over a NACA4412 profile with a 5° angle of attack at chord-based Reynolds number Rec=200,000 is analysed in the present work. The mesh, starting from a coarse resolution, is progressively refined by means of AMR, which allows for high resolution near the wall and wake whereas significantly larger elements are used in the far-field. The resulting mesh is of higher resolution than those in previous conformal cases, and it allows for the use of larger computational domains, avoiding the use of precursor RANS simulations to determine the boundary conditions. All of this with, approximately, 3 times lower total number of grid points if the same spanwise length is used. Turbulence statistics obtained in the AMR simulation show good agreement with the ones obtained with the conformal mesh. Finally, using AMR on wings will enable simulations at Rec beyond 1 million, thus allowing the study of pressure-gradient effects at high Reynolds numbers relevant for practical applications.
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| 22. |
- Tanarro, Álvaro, et al.
(författare)
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Using adaptive mesh refinement to simulate turbulent wings at high Reynolds numbers
- 2019
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Ingår i: 11th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2019.
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Konferensbidrag (refereegranskat)abstract
- The implementation of adaptive mesh refinement (AMR) in Nek5000 is used for the first time on the simulation of the flow over wings. This is done by simulating the flow over a NACA4412 profile with 5 degrees angle of attack at chord-based Reynolds number 200,000. The mesh is progressively refined by means of AMR which allows for high resolution near the wall whereas significantly larger elements are used in the far-field. The resultant mesh shows higher resolution than previous conformal meshes, and it allows for larger computational domains,which avoid the use of RANS to determine the boundary condition, all of this with, approximately, 3 times lower total number of grid points. The results ofthe turbulence statistics show a good agreement with the ones obtained with the conformal mesh. Finally, using AMR on wings leads to simulations at higher Reynolds numbers (i.e. Rec = 850, 000) in order to analyse the effect of adverse pressure gradients at high Reynolds numbers.
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