| 1. |
- Ekman, Petter, 1988-, et al.
(författare)
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Importance of Sub-Grid Scale Modeling for Accurate Aerodynamic Simulations
- 2021
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Ingår i: Journal of Fluids Engineering. - : ASME. - 0098-2202 .- 1528-901X. ; 143:1
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Tidskriftsartikel (refereegranskat)abstract
- The Ahmed body is one of the most well-investigated vehicle bodies for aerodynamic purposes. Despite its simple geometry, the flow around the body, especially at the rear, is very complex as it is dominated by a large wake with strong interaction between vortical structures. In this study, the flow around the 25 deg Ahmed body has been investigated using large eddy simulations and compared to high-resolution particle image velocimetry (PIV) measurements. Special emphasis was put on studying three commonly used sub-grid scale (SGS) models and their ability to capture vortical structures around the Ahmed body. The ability of the SGS models to capture the near-wall behavior and small-scale dissipation is crucial for capturing the correct flow field. Very good agreement between simulations and PIV measurements were seen when using the dynamic Smagorinsky-Lilly and the wall-adopting local eddy-viscosity SGS models, respectively. However, the standard Smagorinsky-Lilly model was not able to capture the flow patterns when compared to the PIV measurements due to shortcomings in the near-wall modeling in the standard Smagorinsky-Lilly model, resulting in overpredicted separation.
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| 2. |
- Fattahi, Sadegh, et al.
(författare)
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Influence of the Timber Shape on the Aerodynamics of a Timber Truck
- 2021
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Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamic improvement and efficiency of regular goods transportation trucks have been a topic of current interest; however, the timber transport industry has not been receiving as much attention. This is due to the small portion of timber transportation vehicles, compared to regular trucks, not justifying the cost of investigating these vehicles experimentally. Since these vehicles travel large parts of their journey at around 80 km/h, their fuel consumption is heavily affected by the aerodynamic resistance. In Sweden in 2015, there were around 2000 vehicles in operation transporting 6 billion ton-km with an average of 0.025 liter Diesel per ton-km. To understand these vehicles’ aerodynamics, and improve on these in the future, the modelling of the timber stacks is of utmost importance. Computational Fluid Dynamics (CFD) simulations have been utilized to conduct this investigation due to recent advancements and the relatively low cost of these simulations compared to an experimental approach. By investigating the influence of geometrical modifications of the stacks on the flow features and accumulated drag, a generic timber stack was created representative of a real stack for a loaded baseline vehicle. It was found that the shorter log length and a shuffling of the logs in the stack exhibit important flow features contributing to drag not present in the other cases. Based on this, a new baseline loaded truck configuration was created with all stacks being identical to each other. This generic stack was built with logs that were 4.25 m long and 0.35 m in diameter, had a smooth surface, and were stacked with a certain displacement in the lengthwise direction.
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