Perform CFD Simulation on Ahmed body and compare the CD value from literature • Literature Used : Assessment of hybrid RANS-LES formulations for flow simulation around the Ahmed body E. Guilmineau∗, G.B. Deng, A. Leroyer, P. Queutey, M. Visonneau, J. Wackers LHEEA, CNRS UMR 6598, Ecole Centrale de Nantes, 1 rue de la Noë, BP 92101, 44321 Nantes Cedex 3, France

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Assignment No. 07
External Aerodynamics (Ahmed body)
29.04.2021
Shivam Choubey
Student No: CFDB30321004

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Objective
• Perform CFD Simulation on Ahmed body and compare the CD
value from literature
• Literature Used : Assessment of hybrid RANS-LES formulations
for flow simulation around the Ahmed body
E. Guilmineau∗, G.B. Deng, A. Leroyer, P. Queutey, M. Visonneau, J. Wackers
LHEEA, CNRS UMR 6598, Ecole Centrale de Nantes, 1 rue de la Noë, BP 92101,
44321 Nantes Cedex 3, France
• This paper presents numerical simulations for the prediction of the flow
around the Ahmed body, RANS (Reynolds Averaged Navier-Stokes)
turbulence model, as EARSM (Explicit Algebraic Stress Model) and two
hybrid RANS-LES models, DES (Detached Eddy Simulation) and IDDES
(Improved Delay Detached Eddy Simulation) models, are used.

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Problem Statement
• Ahmed body is simplified car body created to investigate the turbulence
behavior of newly developed car for complex geometry cases. It
demonstrated all the flow features of an actual car involved in a moving
car.
• In the Ahmed body we only consider external flow subdivision of the
total drag.
• The front end
• The rear slant

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Geometry
Inlet Outlet
Ahmed body
Symmetry Phase
Top
Road
Ahmed body Size Domain Extents
Domain Name Lengths (m)
X+ 5.22 m (Downstream)
X- 2.088 m (Upstream)
Z+ 1.4 m
Z- Symmerty Plan
Y+(Width)Half 0.7405 m
Y- 0.7405 m

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CFD Setting
total volume 1.072174e+01
Maximum Aspect Ratio 3.72838
Number of cells 135045
Aspect Ratio 3.72832e+01
Orthogonal Quality 1.52439e-02

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Results
Velocity Drag cofficent
40 m/s 0.37362436
50 m/s 0.3973156
60 m/s 0.4124633

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Pressure Plots
• This is pressure coutours at 40
m/s
• At midle velocity is less and
Pressure value is nealry
maximum.
• The cornor of body has
maximum velocity
Front
Back

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Vector Plots
Front Back
• Front part of body has less velocity at
center but max. at cornor of body.
• There is no rotation in front of body.
• Back part of body there is more
velocity.
• There is rotation and flow sepration,
shown large and small eddies, and
large wake at back.

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Conclusion
• Ahmed body is used as a benchmark model to analyze the wake flow to
quantify the resistance of an object in a fluid environment. Drag
coefficient plays a significant role in the aerodynamics behaviour of the
vehicle. The slant angle is the major contributing factor for the overall
drag coefficient of vehicle.