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8/3/2019 Effect of Rear End Taper on Drag For
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5/6/12
EFFECT OF REAR
END TAPER ON DRAG
FOR A BLUFF BODY
THARANGA JAYATHUNGA
SID: 3601183
8/3/2019 Effect of Rear End Taper on Drag For
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5/6/12
INTRODUCTION
Aerodynamics is the analysis regarding the air flow
around a body.
Aerodynamic drag force has a direct effect on the fuel
consumption and maximum speed.
Drag coefficient (CD) is one of the governing factor on
the drag force and depends on the body shape.
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INTRODUCTION
Body shape of a vehicle is aerodynamically bluff.
Air flow separation is occurring at the rear end of thevehicle.
There is a developed adverse pressure gradient at the
back.
This is the cause for the pressure drag.
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INTRODUCTION
Degree of taper at the rear end affect the drag force.
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INTRODUCTION
Rear and taper and boat tailing are drag reductionmethods.
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RESEARCH TOPIC
Aim of the research is to generate an understanding of
interaction of side boat tailing and end taper on the
drag of a bluff body.
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METHODOLOGY
CFD simulations was performed and Star CCM+
software Version 6.04.014.
A. Ahmed model and Windsor model tested for
validation.
B. Windsor models is tested for side boat tailing and end
taper interaction.
C. Detail optimization of Windsor model.
D. Tested for theoretical best values for end taper and
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METHODOLOGY
Tapered length of the model.
Length ratio= Length of the tapered/Total length of the model
Ratio used here is 0.2 (209mm).
CAD modeling.
CATIA version 5R20 is used for the CAD modeling.
AhmedCAD.jpg
Windsor CAD.jpg
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METHODOLOGY
Star CCM+ modeling.
Number of cells is around 1 million for every cases that are tested.
Number of faces for each case kept around 300000.
Mesh type is polyhedral.
Prism layer mesh is used for the boundary layers and the thickness is
10mm.
K- model is used for the turbulence modelling.
Number of iterations limit to 1000.
Domainortho.jpg
http://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor%20CAD.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Domainortho.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Domainortho.jpg8/3/2019 Effect of Rear End Taper on Drag For
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METHODOLOGY
Following table is showing all the combinations of side boat tailing
and end taper, that are examined.
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RESULTS
CD value obtained for the Ahmed model is 0.25.
AhmedCAD.jpg
CD value obtained for the Windsor model is 0.295.
Windsor model is in the square back configuration.
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RESULTS
CD for each configuration of the Windsor model.
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RESULTS
Largest value for CD obtained when the end taper angle
80 and side boat tail angle 80 (18% reduction).
S8T8_Vector Scene 1.jpg
Wakeregion.jpg
Windsor_Vector Scene 1.jpg
S8T8_Geometry Scene 6.jpg
stmlin2 - Copy.avi
http://var/www/apps/conversion/current/tmp/scratch25269/S8T8_Vector%20Scene%201.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Wakeregion.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor_Vector%20Scene%201.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/S8T8_Geometry%20Scene%206.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/stmlin2%20-%20Copy.avihttp://var/www/apps/conversion/current/tmp/scratch25269/stmlin2%20-%20Copy.avihttp://var/www/apps/conversion/current/tmp/scratch25269/S8T8_Geometry%20Scene%206.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor_Vector%20Scene%201.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Windsor_Vector%20Scene%201.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Wakeregion.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/S8T8_Vector%20Scene%201.jpg8/3/2019 Effect of Rear End Taper on Drag For
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RESULTS
Wake region is narrowed due to the geometrychanges.
Vortices in the near wake region arecomparatively small.
Pressure loss has been reduced by around 22%due to the changes.
There is a noticeable change in the freestagnation point.
Comparatively more orderly flow is obtained in
here.
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RESULTS
Figure shows the trend of variation of CD With Sideboat tail angle for typical end taper angle.
0 2 4 6 8 10 12
0
2
4
6
8
10
12
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RESULTS
Starting from 00-80 CD is increased and after 80 CD
getting reduced up to 200.
strmlineS8T20.jpg
When the Slant angle increases strength in the 3D trailing
vortices are becoming stronger.
In the far wake region there are two separate flows.
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DETAIL OPTIMIZATION
All the edges as showing in the following figure
is rounded and CD value obtained is 92.
DEtailopt1.jpg
DetailoptCP.jpg
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RESULTS
For the tapered length ratio 0.2 (209mm), end taper
angle 12.50 and side boat tail angle 100 obtained CD
value is 49.
When the tapered length change to 222mm CD
obtained is 54.
http://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpg8/3/2019 Effect of Rear End Taper on Drag For
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CONCLUSIONS
CD value for the (square back) Windsor model is 0.295.
Largest CD is obtained for the side boat tail angle 80 and
end taper angle 80. CD value is 53.
Around 22% base pressure increase compare with square
back.
18% decrease in CD.
Theoretical optimum values for side boat tail end taper given
CD value is 52.
As ect ratios of the boat tail and end ta er have an effect on
http://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpghttp://var/www/apps/conversion/current/tmp/scratch25269/Detailopt%20CP.jpg8/3/2019 Effect of Rear End Taper on Drag For
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CONCLUSIONS
Drag coefficient is influenced by after body rounding.
After body rounding at the side boat tail and end taper 80
configuration gives 31% reduction in drag coefficient.
Aspect ratios of the boat tail and end taper have an effect
on drag reduction.
Drag coefficient is influenced by after body rounding.
Body rounding at the side boat tail and end taper 80
configuration gives 31% reduction in drag coefficient.
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THANK YOU
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