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Effects of Deterministic Wind Gusts on Unsteady Crosswind Aerodynamics of Road Vehicles
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0002-9061-4174
2009 (English)Report (Other academic)
Abstract [en]

The relative flexibility of nowadays numerical methods offers an alternative way to experiments in order to investigate unsteady crosswind aerodynamics in an industrial framework. In this study, time accurate methods such as Detached-Eddy Simulations (DES) are used to simulate the flow. A simple vehicle shape, the so-called Windsor model, is chosen for the model. The ReL of the corresponding flow case is 2.0x106. Then, different deterministic models of wind gusts that are varied in the streamwise and the vertical direction are tested. The magnitude of the gusts models corresponds to a yaw angle of 20o. The aerodynamic loads calculated show a large excess of drag coupled with a reduction of the pitch moment. Although the side force has a smooth variation in the gust, overshoots up to 18% higher than the steady value of yaw moment are also observed.

Place, publisher, year, edition, pages
2009. , 16 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2009:76
National Category
Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-11324OAI: oai:DiVA.org:kth-11324DiVA: diva2:273715
Projects
Eco2 Crosswind stability and unsteady aerodynamics
Note
QC 20101012Available from: 2009-10-23 Created: 2009-10-23 Last updated: 2010-10-12Bibliographically approved
In thesis
1. Numerical Investigation of Unsteady Crosswind Aerodynamics for Ground Vehicles
Open this publication in new window or tab >>Numerical Investigation of Unsteady Crosswind Aerodynamics for Ground Vehicles
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Ground vehicles are subjected to crosswind from various origins such as weather, topography of the ambient environment (land, forest, tunnels, high bushes...) or surrounding traffic. The trend of lowering the weight of vehicles imposes a stronger need for understanding the coupling between crosswind stability, the vehicle external shape and the dynamic properties. Means for reducing fuel consumption of ground vehicles can also conflict with the handling and dynamic characteristics of the vehicle. Streamlined design of vehicle shapes to lower the drag can be a good example of this dilemma. If care is not taken, the streamlined shape can lead to an increase in yaw moment under crosswind conditions which results in a poor handling.

The development of numerical methods provides efficient tools to investigate these complex phenomena that are difficult to reproduce experimentally. Time accurate and scale resolving methods, like Detached-Eddy Simulations (DES), are particularly of interest, since they allow a better description of unsteady flows than standard Reynolds Average Navier-Stokes (RANS) models. Moreover, due to the constant increase in computational resources, this type of simulations complies more and more with industrial interests and design cycles.

In this thesis, the possibilities offered by DES to simulate unsteady crosswind aerodynamics of simple vehicle models in an industrial framework are explored. A large part of the work is devoted to the grid design, which is especially crucial for truthful results from DES. Additional concerns in simulations of unsteady crosswind aerodynamics are highlighted, especially for the resolution of the wind-gust boundary layer profiles. Finally, the transient behaviour of the aerodynamic loads and the flow structures are analyzed for several types of vehicles. The results simulated with DES are promising and the overall agreement with the experimental data available is good, which illustrates a certain reliability in the simulations. In addition, the simulations show that the force coefficients exhibit highly transient behaviour under gusty conditions.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xi, 39 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2009:68
Keyword
Aerodynamics, Vehicle Aerodynamics, Unsteady Aerodynamics, Crosswind, Unsteady Crosswind Aerodynamics, Detached-Eddy Simulations, DES
National Category
Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-11311 (URN)978-91-7415-446-7 (ISBN)
Presentation
2009-11-12, E52, Oscars Backe 14, 3tr, KTH-Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
ECO2 Crosswind Stability and Unsteady Aerodynamics for Ground Vehicles
Available from: 2009-10-23 Created: 2009-10-21 Last updated: 2010-10-12Bibliographically approved

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