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Spectral Density and Time Scales of Velocity Fluctuations in the Wake of a Simplified Car Model
Technical Paper
2012-01-0592
ISSN: 0148-7191, e-ISSN: 2688-3627
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English
Abstract
Although CFD is considered a well-established tool in the
development of car aerodynamics it is obvious that there is still a
strong demand on verification and validation of schemes and models
involved in the numerical codes. This is reflected by the
constantly high number of publications dealing with the matter. One
of the test cases most often adopted for the purpose is the generic
car model proposed by Ahmed et al. This is because of its
geometrical simplicity and the realistic complex flow field which
is reproducibly generated in its wake and makes it a selective test
case. Another reason is the availability of comprehensive
experimental data sets, amongst others the one we reported in an
earlier paper. The velocity data covers the complete flow field
around the model but focuses on the wake region. Besides mean
values it provides turbulence quantities such as Reynolds stresses
and other higher-order statistical moments measured using
laser-doppler anemometry (LDA).
After reviewing the results of numerous CFD approaches and
comparing those to the experimental data it turns out that most
deficiencies arise from the failing prediction of detachment and
reattachment of the flow on the rear body at a slant angle of 25°.
A closer analysis reveals a severe underestimation of the
fluctuating quantities in the wake and most notably in the shear
layers between the outer flow and the recirculation region. This
fact in turn can be directly associated with the difficulties in
predicting reattachment. Because of these findings further LDA
measurements with high spectral resolution were performed at
selected locations. One major aim of the study was to identify the
time scales of the fluctuations and in this way to come to
suggestions what measures are advisable to reduce the uncertainties
both in CFD and experimental results.
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Citation
Lienhart, H. and Pêgo, J., "Spectral Density and Time Scales of Velocity Fluctuations in the Wake of a Simplified Car Model," SAE Technical Paper 2012-01-0592, 2012, https://doi.org/10.4271/2012-01-0592.Also In
References
- Ahmed, S. Ramm, G. Faltin, G. “Some Salient Features of the Time-Averaged Ground Vehicle Wake,” SAE Technical Paper 840300 1984 10.4271/840300
- Lienhart, H. Becker, S. “Flow and Turbulence Structure in the Wake of a Simplified Car Model,” SAE Technical Paper 2003-01-0656 2003 10.4271/2003-01-0656
- ERCOFTAC “ERCOFTAC ‘Classic Collection’ Database” http://cfd.mace.manchester.ac.uk/ercoftac/index.html Sep. 2011
- Menter, F.R. Kuntz, M. “Adaptation of Eddy-Viscosity Turbulence Models to Unsteady Separated Flow Behind Vehicles”, in “The Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains” Lecture Notes in Applied and Computational Mechanics 19 McCallen, Rose Browand, Fred Ross, James 2004 3-540-22088-7
- Bendat, J.S. Piersol, A.G. “Random Data Analysis And Measurement Procedures” John Wiley & Sons New York 978-0471040002 1986
- Nobach, H. “KERN” http://ldvproc.nambis.de/programs/kern.html Sep. 2011
- Nobach, H. “Local time estimation for the slotted correlation function of randomly sampled LDA data” Experiments in Fluids 32 2002 337 345 10.1007/s003480100362
- Bearman, P.W. Near wake flows behind two- and three-dimensional bluff bodies Journal of Wind Engineering and Industrial Aerodynamics 69-71 1997 33-54 0167-6105 10.1016/S0167-6105(97)00146-3