FIELD OF INVENTION
This invention relates to an aerodynamic structure in rear under floor of
vehicle. This leads to reduction in drag and efficient cooling of muffler and
adjacent components.
PRIOR ART
Aerodynamic structure such as air dam, front strakes, rear strake, diffusers
etc. are known to have been provided at various locations under the vehicle
body for reduction of the drag. However, no aerodynamic structure is known to
have been provided under the floor directly in front of fuel tank, suspension
and muffler dissipating exhaust. This is because of the perception that,
placement of any such structure in front of the muffler, fuel tank and
suspension may constitute an obstruction, thereby adversely affecting cooling
of above mentioned components. Also due to the obstruction created using
aero-part, the flow may be diverted towards rear wheels and side wards, which
may increase the drag. Therefore, shape, size and position are key factors in
designing of such aerodynamic structure. In existing structures the underbody
is having under covers which reduces the turbulence level and the flow
configuration gets changed considerably due to it. Also the performance of any
aero part in presence of undercover is very different from performance of aero
part without undercover.
Hence, the present invention proposes an aerodynamic structure in rear under
floor of vehicle (without any under covers) taking into consideration the factors
discussed hereinabove.
OBJECTS OF THE INVENTION
Primary object of the present invention is to provide an aerodynamic structure
in rear under floor of vehicle which reduces drag.
Another object of the present invention is to provide an aerodynamic structure
in rear under floor of vehicle which improves cooling performance.
Further object of the present invention is to provide an aerodynamic structure
in rear under floor of vehicle which is simple in construction, easy in assembly
operations and reliable.
SUMMARY OF THE INVENTION
According to this invention, there is provided an aerodynamic structure in rear
under floor of vehicle comprising of an air dam in front of fuel tank and
another air dam in front of muffler wherein the air dam constituting a
longitudinal member to reduce drag and improve cooling performance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Further objects and advantages of this invention will be more apparent from
the ensuing description when read in conjunction with the accompanying'
drawings and wherein:
Fig. 1 shows: aerodynamic structure in rear under floor of vehicle according to
the present invention.
Fig. 2 shows: one embodiment of air dam of the present invention.
Fig. 2A shows: another embodiment of air dam of the present invention.
Fig. 3 shows: assembly of components in rear under floor of vehicle.
Fig. 4 shows: still another embodiment of air dam of the present invention.
Fig. 5 shows: air dam with guide according to present invention.
Fig. 6 shows: air flow in rear under floor of a vehicle without air dam.
Fig. 7 shows: air flow in rear under floor of a vehicle with air dam.
Fig. 8 shows: CFD simulation drag contours in respect of fig. 6 indicating more
drag.
Fig. 9 shows: CFD simulation drag contours in respect of fig. 7 indicating less
drag.
Fig. 10 shows: drag in a vehicle without air dam.
Fig. 11 shows: drag in a vehicle with air dam.
Fig. 12 shows: less flow on rear under floor without air dam.
Fig. 13 shows: mare flow on rear under floor with air dam.
Fig. 14 shows: both air dam of same size and shape (symmetrical).
Fig. 15 shows: both air dam of different size and shape (Asymmetrical).
Fig. 16 shows: flow details (a) without dam (b) with dam.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO
ACCOMPANYING DRAWINGS:-
The present invention discloses an aerodynamic structure in rear under floor of
vehicle. The aerodynamic structure of the instant invention comprises a pair of
air dams in the rear under floor of vehicle. Now, reference may be made to fig.
1. One air dam (1) is located in front of the muffler (M) and another air dam (2)
is positioned in front of the fuel tank (F). Said air dams are provided in
proximity to the suspension(s) of vehicle as shown.
Now, reference may be made to fig. 2 wherein the air dam comprising of a
longitudinal member having a flat top surface. (3) in contact with the rear under
floor of vehicle and a lower surface (4) with side surfaces (5, 6) as shown. The
upper flat surface can be provided with a groove (G) to accommodate pipes
such as brake and fuel pipes (5, P) as shown in fig. 3.
However, the flat top surface may be provided without the groove as shown in
fig. 2A.
The lower surface may be having a plurality of serrations or slots as shown in
fig. 4. The slot can have different width, depth or cross section (preferably
rectangular or trapezoidal).
Alternatively, the lower surface may be curved surface.
Further, another embodiment of present invention comprises a tapered cross
I section.
The embodiments mentioned hereinabove are exemplary embodiments without
I, restricting scope of the invention to the. same. Thus, several variations can be
done to the shape of the block serving the same purpose.
In addition to the shape, dimension and position of the air dam also play
important role. 1,. Both the air dam can have same or different shape and dimension relying on
the vehicle layout.
Referring to fig. 3, central air dam requires clearance from fuel and brake pipe
lines (5, P).
Therefore, left and right side air dam (3a, 3b) can be same or different in shape,
size and geometry, which is provided in front of muffler (2) and fuel tank (1) on
-6-
rear floor (6). The shape, size and geometry are optimized to meet requirement
and performance of vehicle.
Now, reference may be made to fig. 5.
In addition to the above, said air dam may be provided with a guide (D)
adjacent to at least one side surface (5, 6) to supplement the air flow. Said
guide is provided at an angle (a)w ith thk air dam.
The air dam can be mounted on the rear under floor by means of clips/clamp,
welds, and screws etc. without restricting scope of the invention to the same.
However, clamp is preferably used to reduce assembly cost and time.
The air dam can be made of material such as polypropylene, rubber, steel.
Thus, the above is given as example. Other suitable mountings and materials
readily apparent to person skilled in the art are understood to be within
purview of the invention.
Mechanism of drag reduction
The central air-dam redistributes the flow velocity under the vehicle body and ,
also changes the direction of the flow. Initially when the air-dam is not present
the pressure and velocity at point 1 and 2 as shown in figure 16(a) is not
significantly different. Also the flow hits the muffler edges and generates
additional turbulence which increases the drag. Also a part of the flow between
the muffler and rear floor gap gets entrapped due to lack of pressure difference
and increases the stagnation which in turn increases the drag.
When the air-dam is added the pressure difference between points 3 and 4
increases. This pressure difference tries, to draw more air inward as shown by
flow lines in figure 16 (b). Also this inward drawing of air prevents the air from
..,. . ., . . - - . ........, .. .... :/ ;.:.f i:t'c"j wards thc: side ward or towartls icirc. '?his has ti::l:)cd in rcdu:::.ion af
stagr:atiori as the earlier entrapped air also has sufficient pressure difference to
=eve and balance the flow velocity, which leads to decrease in drag. A!sc as the
. - i A - . ,xi\,!. ..; , bends downward slightly the turbulence generated due to hitting on
.- .. - .:A-p:.. 7. , : : : : :cr cdgc is also rcduccd. Also bcttcr pressure restoration was obscrvcd
< < .
+$. iii,iiviti id,,: ,. the vehicle at rear bumper and backdoor region due to this balanced
underflow. '!'he niovement of entrapped air has helped in better cooling also.
I:; ',ills regard, reference may be made to fig. 6 arid fig. '7, in which the ander
.- rr,! '
"""7 is liijiii suk)jf;cied io direct flow and .t)ci-iding t>f fow respectively. t seir
7.c -,z,?,>:Ti,.,r,.+,;; ,i,,vc CFD simulation drag contours arc shown ir, fig. 8 and 9 respectively.
--, -qt; r= .== ,%+s e sm%$6-e eq - ,,, ,%,, ,;,$ Wind tunnel results for drag reduction (fig. 10 and f If
- -- Value - - - - -
cerltra! ZIT
Ccnfiguratiori Simulation
results Non
dimensional
( Coefficient of Drag Cd !
+ +Ti,Li ,,Lii,ii in Cd value indicates reductiori in drag.
--
Wind Tunricl results
Non dimensional
{ Coefficient cf Drag Cd
Value )
s ~-E ~ = ~Cno~srs;li=nqz d ue to -. -
2%. -- - --- .. 2- - -- =--:2= - == -z-z-= - - =:e -+:z-- =$.% -- +as=-?: ,,--d4-G %kiV" 1;:;s
C.'D 2;;a;ysis was carried out to find the effect of cot;iing due to adultion
,. . . .
o: the ax--dam.
Due to bending of the flow, pressure reduces directly behind the air-dam
and a pressure gradient is created across the component length. This
pressure gradient draws the air from the sides and hence improves the
cooling. Now, reference may be made to fig. 12 and 13indicating less flow
and more flow respectively.
Now, reference may be made to fig. 14 indicating both central dams of same
dimension and shape, which leads to 5.7% reduction in coefficient of drag (Cd).
Further, referring to fig. 15 showing both central dams of different dimension
and shape, which results in 3.6% reduction in coefficient of drag(Cd).
Thus, the height and length of central dam can be optimized for further
reduction in drag depending upon the requirements of vehicle ground
clearance.
Advantageous Features
Reduction of drag by redistribution of velocity and pressure.
Improved cooling performance.
~aintenance of required clearance from overhead conveyor hanger,
muffler, brake pipe, fuel pipe and ground.
Reduced stagnation in underbody and. hence improvement in the drag
due to redistribution of velocity.
More air flow towards muffler, thereby improving cooling due to pressure
gradient created by the air-dam.
It is to be noted that the present invention is susceptible to modifications,
adaptations and changes by those skilled in the art. Such variant
embodiments employing the concepts and features of this invention are
intended to be within the scope of the present invention, which is further set
forth under the following claims:-

WE CLAIM:
1. An aerodynamic structure in rear under floor of vehicle comprising of an
air dam in front of fuel tank and another air dam in front of muffler
wherein the air dam constituting a longitudinal member to reduce drag
and improve cooling performance.
2. An aerodynamic structure as claimed in claim 1, wherein the
longitudinal member comprising of a flat top surface in contact with the
rear under floor of vehicle.
3. An aerodynamic structure.as claimed in claim 1 or 2, wherein the top flat
surface may be provided with a groove to accommodate pipeline.
4. An aerodynamic structure as claimed in any of the preceding claims,
wherein the longitudinal member comprising of a bottom surface
provided with a plurality of serrations/ slots.
5. An aerodynamic structure as claimed in any of the preceding claims,
wherein the lower surface may be curved surface.
6. An aerodynamic structure as claimed in any of the preceding claims,
wherein the air dam may have a tapered cross section.
7. An aerodynamic structure as claimed in any of the preceding claims,
wherein said air dam may be provided with a guide adjacent to atleast
one side surface to supplement air flow.
8. An aerodynamic structure as claimed in any of the preceding claims,
wherein said air dams may have same or different shape and size relying
on the vehicle layout.
9. An aerodynamic structure as claimed in any of the preceding claims,
wherein the air dam maintains required clearance such as herein described.
10. An aerodynamic structure as claimed in any of the preceding claims is associated with the advantageous features such as herein described.