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Aerodynamics of an Unloaded Timber Truck - A CFD Investigation
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0001-6634-797X
ANSYS Sweden, Sweden.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0001-5526-2399
2016 (engelsk)Inngår i: SAE International Journal of Commercial Vehicles, ISSN 1946-391X, E-ISSN 1946-3928, Vol. 9, nr 2, s. 217-223Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Reducing energy consumption and emissions are ongoing challenges for the transport sector. The increased number of goods transports emphasize these challenges even more, as greenhouse gas emissions from these vehicles increased by 20 % between 1990 and 2013, in Sweden. One special case of goods transports is the transport of timber. Today in Sweden, around 2000 timber trucks transport around six billion ton kilometers every year. For every ton kilometer these vehicles use around 0.025 liter diesel, and there should exist large possibilities to reduce the fuel consumption and the emissions for these vehicles. Timber trucks spend most of their operation time travelling in speeds of around 80 km/h. At this speed aerodynamic drag contributes to around 30 % of the total vehicle resistance, which makes the aerodynamic drag a significant part of the energy consumption. One of the big challenges with timber trucks is that they travel unloaded half of the time. This put higher demands on possible drag reduction modifications, as they need to function and be practical for both when the timber truck is loaded and unloaded. In this study an unloaded timber truck has been investigated by use of computational fluid dynamics. The recently released Stress Blended Eddy Simulation model has been used for simulating the flow over a timber truck at a Reynolds number of 1.1 million, based on the square root of its frontal area. From the results it could be seen that 52.8 % of the drag is generated by the cab. By investigating a drag reduction device that covered the gap between the bulkhead and the first stake pair, a drag reduction up to 6.7 % was possible, which shows potential for simple modifications that not influence the daily usage.

sted, utgiver, år, opplag, sider
SAE INT , 2016. Vol. 9, nr 2, s. 217-223
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-163998DOI: 10.4271/2016-01-8022ISI: 000389233800010OAI: oai:DiVA.org:liu-163998DiVA, id: diva2:1412262
Tilgjengelig fra: 2020-03-05 Laget: 2020-03-05 Sist oppdatert: 2020-04-02
Inngår i avhandling
1. Important Factors for Accurate Scale-Resolving Simulations of Automotive Aerodynamics
Åpne denne publikasjonen i ny fane eller vindu >>Important Factors for Accurate Scale-Resolving Simulations of Automotive Aerodynamics
2020 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Road transports are responsible for almost 18 % of the greenhouse gas emission in Europe and are today the leading cause of air pollution in cities. Aerodynamic resistance has a significant effect on fuel consumption and hence the emission of vehicles. For electric vehicles, emissions are not affected by the aerodynamics as such but instead have a significant effect on the effective range of the vehicle.

In 2017, a new measurement procedure was introduced, Worldwide Harmonized Light Vehicles Test Procedure (WLTP), for measuring emissions, fuel consumption, and range. This procedure includes a new test cycle with increased average driving speed compared to the former procedure, which thereby increases the importance of the aerodynamic resistance, as it drastically increases with speed. A second effect is that the exact car configuration sold to the customer needs to be certified in terms of fuel consumption and emissions. The result is that every possible combination of optional extras, which might affect the aerodynamic resistance, needs to be aerodynamically analyzed and possibly improved. From 2021, the European Commission will introduce stricter emission regulations for new passenger cars, with the fleet-wide average lowered to 95 grams CO2=km, which puts an even higher demand on achieving efficient aerodynamics.

Virtual development of the aerodynamics of road vehicles is today used to a great extent, using Computational Fluid Dynamics, as it enables faster and cheaper development. However, achieving high accuracy for the prediction of the flow field and aerodynamic forces is challenging, especially given the complexity of both the vehicle geometry in itself and the surrounding flow field. Even for a simplified generic bluff body, accurately predicting the flow field and aerodynamic forces is a challenge. The main reason for this challenge of achieving results with high accuracy is the prediction of the complex behavior of turbulence. Scale-resolving simulation (SRS) methods, such as Large Eddy Simulation (LES), where most of the turbulent structures are resolved has in many studies shown high accuracy but unfortunately to a very high computational cost. It is primarily the small turbulent structures within the near-wall region that requires a _ne resolution in both space (the mesh) and in time. This fine resolution is the reason for the very high computational cost and makes LES unfeasible for practical use in industrial aerodynamic development at present and in the near future. By modeling the turbulent structures within the near-wall region using a Reynolds-Averaged Navier-Stokes (RANS) model, and resolving the turbulence outside the region with a LES model, a coarser resolution is possible to use, resulting in significantly lower computational cost. Which used RANS model is of high importance, and especially how much turbulent viscosity the model generates, as too high values can result in suppression of the resolved turbulence.

The transitioning between the RANS and LES regions have a significant effect on the results. Faster transition enables more resolved turbulence, favorable for higher accuracy, but needs to be balanced with sufficient shielding of the RANS region. If resolving the turbulence occurs within the near-wall region, and the mesh is not sufficiently fine, it can result in poor accuracy.

By increasing the time-step size and disregarding best-practice guides, the computational cost can be significantly reduced. The accuracy is reasonably insensitive to the larger time step sizes until a certain degree, thereby enabling computationally cheaper SRS to achieve high accuracy of aerodynamic predictions needed to meet present and future emission regulations.

sted, utgiver, år, opplag, sider
Linköping: Linköping University Electronic Press, 2020. s. 96
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2068
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-164926 (URN)10.3384/diss.diva-164926 (DOI)9789179298630 (ISBN)
Disputas
2020-05-05, C3 C-Building, Campus Valla, Linköping, 13:15 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Linköpings universitetSwedish Energy Agency, 40281-1Swedish National Infrastructure for Computing (SNIC)Swedish Research Council, 2016-07213
Tilgjengelig fra: 2020-04-02 Laget: 2020-04-02 Sist oppdatert: 2020-05-11bibliografisk kontrollert

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