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Aerodynamics simulations of ground vehicles in unsteady crosswind
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ground vehicles, both on roads or on rail, are sensitive to crosswinds and the handling, travelling speeds or in some cases, safety can be affected. Full modelling of the crosswind stability of a vehicle is a demanding task as the nature of the disturbance, the wind gust, is complex and the aerodynamics, vehicle dynamics and driver reactions interact with each other. 

One of the objectives of this thesis, is to assess the aerodynamic response of simplified ground vehicles under sudden strong crosswind disturbances by using an advanced turbulence model. In the aerodynamic simulations, time-dependant boundary data have been used to introduce a deterministic wind gust model into the computational domain. 

This thesis covers the implementation of such gust models into Detached-Eddy Simulations (DES) and assesses the overall accuracy. Different type of grids, numerical setups and refinements are considered. Although the overall use of DES is seen suitable, further investigations can be foreseen on more challenging geometries. 

Two families of vehicle models have been studied. The first one, a box-like geometry, has been used to characterize the influence of the radius of curvature and benefited from unsteady experimental data for comparison. The second one, the Windsor model, has been used to understand the impact of the different rear designs. Noticeably, the different geometries tested have exhibited strong transients in the loads that can not be represented in pure steady crosswind conditions.

The static coupling between aerodynamics and vehicle dynamics simulations enhances the comparisons of the aerodynamic designs. Also, it shows that the motion of the centre of pressure with respect the locations of the centre of gravity and the neutral steer point, is of prime interest to design vehicles that are less crosswind sensitive. Recommendations on the future work on crosswind sensitivity for ground vehicles are proposed at the end of this thesis.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. , xx, 67 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2011:82
Keyword [en]
Detached-Eddy Simulations; Crosswind; Aerodynamics;
National Category
Aerospace Engineering Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-50242ISBN: 978-91-7501-196-7 (print)OAI: oai:DiVA.org:kth-50242DiVA: diva2:461388
Public defence
2011-12-16, E1, Lindstedsvägen 3, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Projects
crosswind stability and unsteady aerodynamics
Note

QC 20111206

Available from: 2011-12-06 Created: 2011-12-03 Last updated: 2013-06-25Bibliographically approved
List of papers
1. 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
2. Detached-Eddy simulations of simplified vehicles in steady and unsteady crosswind
Open this publication in new window or tab >>Detached-Eddy simulations of simplified vehicles in steady and unsteady crosswind
(English)Article in journal (Other academic) Submitted
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-50470 (URN)
Note
QS 2011 QS 20120326Available from: 2011-12-06 Created: 2011-12-06 Last updated: 2012-03-26Bibliographically approved
3. Detached-Eddy Simulations of the Effects of Different Wind Gust Models on the Unsteady Aerodynamics of Road Vehicles
Open this publication in new window or tab >>Detached-Eddy Simulations of the Effects of Different Wind Gust Models on the Unsteady Aerodynamics of Road Vehicles
2010 (English)In: ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels (FEDSM2010), 2010, 2605-2614 p.Conference paper, Published paper (Refereed)
Abstract [en]

Therelative flexibility of nowadays simulation techniques offers an alternative wayto experiments in order to investigate unsteady crosswind aerodynamics inan industrial framework. In this study, time-accurate simulations, Detached-Eddy Simulations(DES), are used to simulate the flow around a simplevehicle shape, the so-called Windsor model. The ReL of thecorresponding flow case is 2.0 · 106. The influence ofdifferent deterministic models of wind gusts on the aerodynamic loadsand moments are studied. The wind gusts are varied inthe stream-wise and the vertical direction. The magnitude of thegusts models corresponds to a yaw angle of 20°. Theaerodynamic loads calculated show a large excess of drag coupledwith a reduction of the pitch moment. In addition, althoughthe side force has a smooth variation in the gust,overshoots up to 18% higher than the steady value ofyaw moment are also observed.

National Category
Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-50487 (URN)10.1115/FEDSM-ICNMM2010-30454 (DOI)000307365700290 ()2-s2.0-80055016238 (Scopus ID)978-0-7918-4948-4 (ISBN)
Conference
3rd Joint US-European Fluids Engineering Division Summer Meeting
Note

QC 20111206

Available from: 2011-12-06 Created: 2011-12-06 Last updated: 2013-06-11Bibliographically approved
4. Unsteady mechanisms in crosswind aerodynamics for ground vehicles
Open this publication in new window or tab >>Unsteady mechanisms in crosswind aerodynamics for ground vehicles
2011 (English)Report (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 22 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2011:85
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-50497 (URN)
Note
QC 20111206Available from: 2011-12-06 Created: 2011-12-06 Last updated: 2011-12-06Bibliographically approved
5. Numerical study of design alterations affecting the crosswind characteristics of a generic road vehicle model
Open this publication in new window or tab >>Numerical study of design alterations affecting the crosswind characteristics of a generic road vehicle model
2010 (English)In: Eighth World MIRA International Vehicle Aerodynamics Conference, 2010Conference paper, Published paper (Refereed)
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-50500 (URN)
Conference
Eighth World MIRA International Vehicle Aerodynamics Conference
Note

QC 20111206

Available from: 2011-12-06 Created: 2011-12-06 Last updated: 2016-05-23Bibliographically approved
6. Static coupling between detached-eddy simulations and vehicle dynamic simulation of a generic road vehicle model in unsteady crosswind with different rear configurations
Open this publication in new window or tab >>Static coupling between detached-eddy simulations and vehicle dynamic simulation of a generic road vehicle model in unsteady crosswind with different rear configurations
(English)Article in journal (Other academic) Submitted
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-50502 (URN)
Note
QS 2011 QS 20120326Available from: 2011-12-06 Created: 2011-12-06 Last updated: 2012-03-26Bibliographically approved

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