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Numerical Investigation of Unsteady Crosswind Aerodynamics for Ground Vehicles
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
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 [en]
Aerodynamics, Vehicle Aerodynamics, Unsteady Aerodynamics, Crosswind, Unsteady Crosswind Aerodynamics, Detached-Eddy Simulations, DES
National Category
Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-11311ISBN: 978-91-7415-446-7 (print)OAI: oai:DiVA.org:kth-11311DiVA: diva2:273411
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
List of papers
1. Numerical Investigation of Unsteady Crosswind Vehicle Aerodynamics using Time-Dependent Inflow Conditions
Open this publication in new window or tab >>Numerical Investigation of Unsteady Crosswind Vehicle Aerodynamics using Time-Dependent Inflow Conditions
2008 (English)In: Seventh World MIRA International Vehicle Aerodynamics Conference, 2008Conference paper, Published paper (Refereed)
Abstract [en]

Transient disturbances concerning ground vehicles are not only due to rail or road irregularities but are also caused by unsteady ambient wind conditions. This study presents a numerical investigation of unsteady crosswind aerodynamics by using the commercial software STAR-CD from CD-Adapco. The unsteadiness of the aerodynamics is introduced through time-dependent inflow boundary conditions that describe a jet flow according to Schlichting [1]. The purpose of this study is to explore the validity of the commonly used numerical methods (URANS and DES) for the current crosswind application. To this end, simplified vehicle geometries are utilized, for which the experimental results of Chadwick et al. [2] are used as reference data.

Keyword
Vehicle Aerodynamics, crosswind aerodynamics, crosswind stability, Detached-Eddy Simulation
National Category
Fluid Mechanics and Acoustics Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-11322 (URN)978-1-906400-05-7 (ISBN)
Conference
7th MIRA International Vehicle Aerodynamics Conference, Coventry, 22-23 October, 2008.
Projects
ECO2 crosswind stability and unsteady aerodynamics
Note

QC 20101012

Available from: 2009-10-23 Created: 2009-10-23 Last updated: 2016-05-23Bibliographically approved
2. An Assessment of Detached-Eddy Simulations of Unsteady Crosswind Aerodynamics of Road Vehicle
Open this publication in new window or tab >>An Assessment of Detached-Eddy Simulations of Unsteady Crosswind Aerodynamics of Road Vehicle
2011 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 87, no 1, 133-163 p.Article in journal (Refereed) Published
Abstract [en]

An extensive study of the mesh requirements when simulating unsteady crosswind aerodynamics for industrial applications is conducted and reported in this article. Detached-Eddy Simulations (DES) of a simple car geometry under headwind, steady crosswind and time-dependent wind gust are analysed for different meshes and flow cases using a commercial software, STAR-CD. The typical Reynolds number of the cases studied is 2.0x106 based on the vehicle length. Mesh requirements for capturing the time development of the flow structures during a gust is provided. While respecting these requirements, the aerodynamic coefficients can be reliably calculated. Using turbulence methods like DES in order to resolve the flow scales provides a significant insight for designing a ground vehicle and, due to the reasonable computational times involved, can be incorporated in a design process in a near future.

Keyword
Unsteady crosswind aerodynamics, Detached-Eddy Simulation, Wind gust, Mesh, Vehicle aerodynamics
National Category
Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-11323 (URN)10.1007/s10494-011-9333-4 (DOI)000291661700006 ()2-s2.0-79959308216 (Scopus ID)
Projects
ECO2 crosswind stability and unsteady aerodynamics
Funder
Swedish e‐Science Research CenterTrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20101012 Updated from submitted to published.Available from: 2009-10-23 Created: 2009-10-23 Last updated: 2017-12-12Bibliographically approved
3. Effects of Deterministic Wind Gusts on Unsteady Crosswind Aerodynamics of Road Vehicles
Open this publication in new window or tab >>Effects of Deterministic Wind Gusts on Unsteady Crosswind Aerodynamics of Road Vehicles
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.

Publisher
16 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2009:76
National Category
Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-11324 (URN)
Projects
Eco2 Crosswind stability and unsteady aerodynamics
Note
QC 20101012Available from: 2009-10-23 Created: 2009-10-23 Last updated: 2010-10-12Bibliographically approved

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