Under Tray Diffuser of a FSAE Race car

This article discusses the under tray diffuser of a FSAE race car and its impact on performance. It covers current undertray technology, CFD simulation of vehicle aerodynamics, FSAE aerodynamic devices, and more. The article also includes diagrams and references to support the information presented.

Running head: UNDER TRAY DIFFUSER OF A FSAE RACE CAR
Under Tray Diffuser of a FSAE Race car
Name of the Student
Name of the University
Author’s Note

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UNDER TRAY DIFFUSER OF A FSAE RACE CAR
Table of Contents
Introduction......................................................................................................................................3
Current Undertray Technology........................................................................................................3
CFD Simulation of Vehicle Aerodynamics.....................................................................................5
FSAE Aerodynamic Devices...........................................................................................................8
Front Wing.......................................................................................................................................9
Conclusion.....................................................................................................................................10
References......................................................................................................................................12

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UNDER TRAY DIFFUSER OF A FSAE RACE CAR
Introduction
Aerodynamic improvements in automotive racing have been a vital effect on the
performance of the vehicle. Recent developments in Formula SAE (Society of Automotive
Engineers) have included in design of aerodynamics devices including inverted wings and
undertrays for improvising performance (Tyagi and Madhwesh 2017). Computational Fluid
Dynamics simulations have been used for iterating design and identify the impact of downforce
developed of several parameters including speed, height and ride. Design of aerodynamic
elements of race cars has been complex
This work focuses on a literature of undertray technology has been presented and design
of an undertray for Global Formula Racing car. An Undertray Diffuser is just as the front and
back wing of race cars. The design of Formula SAE undertray has been developed using CFD
and on-track testing for determining actual vehicle perfirmnece on road.
Current Undertray Technology
The concept of understray has been developed for close proximity of vehicle on ground
and creating a venture effect under the vehicle. Therefore, as like a venture, there will be a
nozzle that helps in increasing speed of the vehicle. This nozzle help in increasing velocity of air
underneath vehicle and throat where maximum throat is provided by the diffuser (Khokhar and
Shirolkar 2015). This condition can be equalize with the Bernouli’s Equation that describes the
local velocity increases relative to free stream velocity as local pressure get decreased. Using
Bernoulli's equation in case of steady, incompressible, in viscid flows along a streamline,
theoretical pressure drop at the constriction is given by
𝑃1 − 𝑃2 = 𝜌 2 (𝑢2 2 − 𝑢1 2)

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where is ρ density of fluid, u1 is the slower fluid velocity where pipe is wider, u2 is faster fluid
velocity where pipe is narrower.
Figure 1: Venturi effect Inside a Venturi tube
(Source: Biswal, Prasanth and Naranje 2016)
Downforce can be created by using this low pressure under designed vehicle. The
efficiency of an udertray has been proper as the efficiency of the diffusion. The high visibility
relative to rest of undertray has been creating some misconception in race car industry for
working if diffuser. As argued by Trzesniowski (2017), diffuser helps in creating a downforce of
the undertray and it expands air under vehicle causing lowered pressure.
Figure 2: Race cars use inverted airplane wings to produce downforce instead of lift

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UNDER TRAY DIFFUSER OF A FSAE RACE CAR
(Source: Grabis and Agarwal 2017)
However, both this concepts abut diffuser have been driven wrong as the diffuser has
been role for slowing down air under vehicle back down for free streaming and reducing drag for
increasing the overall efficiency of undertray. The location of entrance o diffuser has been
affecting low pressure in the understray of vehicle. The angle of diffuser has been relative to the
affect over the ground that has been affecting the magnitude of downforce. It has been highest
angle without flow of separation for generating maximum downforce (Bosch 2018). Two-
dimensional simulation of diffuser angle has been showing maximum downforce for reaching an
angle of 5 degree. As commented by Milan (2018), experiments and 3D simulation has been
effective in maintaining these changes in the pressure. A vortex helps in adding a rotational
component to the velocity by decreasing the pressure along its length, therefore, vortex flow has
been adding their energy in flowing and create delay in separation allowing larger diffuser
angles. Vortices has been used in other parts of the undertray (Prasanth et al. 2016). Large vortex
generators has been replaced in the entrance of the understray that helps vortices in travelling
along the length of the vehicle. However, all of these ideas can be put together for creating an
effective undertray for producing a large amount of downforce with survey small for increasing
drag.
CFD Simulation of Vehicle Aerodynamics
As commented by Hady (2018), CFD simulation can help in clearing up the interactions
of flow around the vehicle. This solution has been used to observe pressure, downforce, velocity
and drag by other fluid properties. However, there has been some work done in the 2D
simulation of airfoils. As suggested by Mercadal Llobera (2017), fizzing up the CFD model in
geometry of Computer Aided Design (CAD) package has been imported for creating the design

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of vehicle (Hady 2018). The use of the CAD has been beneficial for the designing the outer
layer of the race car. The geometry of the design has been properly maintained and balanced in
the CAD that might help in generating velocity.
Figure 3: Drag force acting on a moving race car
(Source: Grabis and Agarwal 2018))
The aberrance in the wind tunnel of the race car has been kept long for proper flow of
fluid. However, the exit to the wind tunnel has been laced at many car lengths. Therefore, the
simulation of the open wheeled car must be with tires rotating on ground for setting a movement
on ground. The CFD model have helped in rotating tires that will help in capturing the behavior
of flow. The airflow in the race car has been very turbulent, therefore a model needs to be
verification of simulation of flow (Soliman, Martins and Schommer 2015). There are four major
turbulence models in the automotive industry including k-ε, k-ω, Lattice-Boltzmann and Large
Eddy Simulation (LES). Direct Numerical Simulation (DNS) has been applied in automotive
industry that requires large mesh numbers for computing power and time for traditional design
turn around. Therefore mesh numbers have been widely depending on simulation of
computational power. These simulations have been beneficial for designer as there can be visual
ads and data of interactions (Bradford, Montomoli and D’Ammaro 2014). Therefore, this

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simulation has been set up using commercial program Star-CCM+. Imported CAD geometry has
been used in all surfaces. A box has been made along geometry for serving as boundary
condition for providing extra space 1 car length in front, 3 lengths rear and 1 length to side.
Figure 4: Simulation geometry with labels
(Source: Mathijsen 2017)
Mesh size has been chosen that helps in detailing vehicle as accurately captured for cell
count on order of a million. Therefore, a prism layer mesh consisting of live layers have been
included near wall effects. The mess has been allowed for growing large sizes away from the
vehicle geometry for reducing cell count in detailed solution (Dahlberg 2014).

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UNDER TRAY DIFFUSER OF A FSAE RACE CAR
Figure 5: Prism layer mesh detail
(Source: Unni 2017)
FSAE Aerodynamic Devices
There have been various upgrades in Aerodynamics as FSAE car development has
become easy for the industry. The speed of the race cars have been increased with laps of time.
The ugradation in the technology in automotive dusty have helped in developing a safer
approach towards the development of race cars. The main aim of the companies have been
reducing risks of accidents due to high speed of race cars (Kalyan, Rajak and Annamalai 2017).
They have focused on developing aerodynamic devices having balanced body and design with
high speed. Streamlined updates are one of key regions in a FSAE auto improvement which can
undoubtedly have effect in opposition occasions, with coordinate impact on best and cornering
speed. Contingent upon required objectives of each group being referred to, they can either
diminish drag and increment top speed, increment down power and drag levels for cornering
paces, or go for a harmony between two.

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Streamlined redesigns come in a wide range of structures and have developed generally
from the beginning of FSAE rivalries with a streamline plan in the plain start. This was trying to
expand generally top speeds and played a major effect on outline headings. Most regular gadgets
and numerous others are utilized to influence FSAE autos to build their streamlined proficiency,
this thusly keeps the tires planted on the ground and expand hold (Weingart 2015). There are
numerous contrasts between "open wheel" and "shut wheel" streamlined plans and a few parts
are not material in two determinations but rather they share shared objective to increment
downforce levels with the insignificant measure of drag (Patidar and Bhamidipati 2014).
Delivering downforce without formation of drag is incomprehensible and it is dependably an
exercise in careful control to achieve the best exchange off and augment streamlined
productivity.
Front Wing
The initial segment of a FSAE auto which interacts with air is certainly front wing. This
implies it initial segment of auto that associates with air, thusly it has imperative part to decide
under-stream course through whatever remains of auto. Front wings are ordinarily mounted near
suspension, or even on mounts so as to transmit descending heaps of power as successfully as
could be expected under circumstances and make downforce so as to press feels worn out on the
front wheels into ground and produce higher hold levels. The front wing creates up 20% - 30%
of aggregate downforce on the auto (Volk 2014). The fundamental plan of a FSAE front wing is
for most part a multi-component airfoil which is normally firmly coupled airfoils comprising of
two or even four components stretched out from two sides of nosecone, with mobile folds fused
in outline to alter of approach. The wing's principle component is generally a symmetric airfoil

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which is brought up in middle keeping in mind end goal to enable a somewhat better wind
current to the underfloor, however it additionally lessens the wings ride stature affectability.
In any case, both this ideas adjoin diffuser have been driven wrong as the diffuser has
been part to back off air under vehicle withdraw with the expectation of complimentary spilling
and decreasing drag for expanding the general proficiency of undertray (Janson and Piechna
2015). The area of passageway o diffuser has been influencing low weight in the understray of
vehicle. The point of the diffuser has been with respect to the effect over the ground that has
been influencing the size of downforce. It has been the most elevated point without stream of
partition for creating greatest downforce. Two-dimensional recreation of diffuser edge has been
demonstrating greatest downforce for achieving an edge of 5 degree. As remarked by Leyva
(2014), investigations and 3D reenactment has been successful in keeping up these adjustments
in the weight. A vortex helps in adding a rotational segment to the speed by diminishing the
weight along its length, hence, the vortex stream has been including their vitality in streaming
and make delay in partition permitting bigger diffuser points. Vortices has been utilized in
different parts of the undertray (Milan 2018). Huge vortex generators has been supplanted in the
passageway of the understray that helps vortices in going along the length of the vehicle. In any
case, these thoughts can be assembled for making a viable undertray for delivering a lot of
downforce with review little to increase drag.
Conclusion
It can be concluded that the downforce of the racing car have been an important factor in
increasing the speed of race car. The abnormality in the breeze passage of the race auto has been
kept yearn for appropriate stream of liquid. In any case, the exit to the breeze burrow has been
bound at numerous auto lengths. Consequently, the recreation of the open wheeled auto must be

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with tires pivoting on ground for setting a development on ground. The CFD show have helped
in pivoting tires that will help in catching the conduct of the stream. The wind current in the race
auto has been extremely fierce, in this manner a model should be confirmation of reenactment of
the stream.

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References
Biswal, S., Prasanth, A. and Naranje, V.G., 2016. Design and Optimization of the Diffuser for
the Formula SAE Car for Improved Performance. In Proceedings of the World Congress on
Engineering (Vol. 2).
Bosch, T., 2018. Aerodynamic Package FSAE: Summary Report. The UNSW Canberra at
ADFA Journal of Undergraduate Engineering Research, 9(2).
Bradford, J., Montomoli, F. and D’Ammaro, A., 2014. Uncertainty quantification and race car
aerodynamics. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of
Automobile Engineering, 228(4), pp.403-411.
Dahlberg, H., 2014. Aerodynamic development of Formula Student race car.
Grabis, M. and Agarwal, R.K., 2017. Computational Fluid Dynamics Analysis of High Lift,
Single Element, Inverted Airfoils in Ground Effect for an FSAE Car Front Wing.
Grabis, M. and Agarwal, R.K., 2018. Computational Fluid Dynamics Analysis of High Lift,
Inverted Airfoils in Ground Effect.
Hady, N.A., 2018. Numerical Three-Dimensional Study of an Open Wheel Race Car
Undertray (No. 2018-01-0723). SAE Technical Paper.
Janson, T. and Piechna, J., 2015. Numerical analysis of aerodynamic characteristics of a of high-
speed car with movable bodywork elements. Archive of Mechanical Engineering, 62(4), pp.451-
476.

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UNDER TRAY DIFFUSER OF A FSAE RACE CAR
Kalyan, N.V.S., Rajak, D.K. and Annamalai, L., 2017. INFLUENCE OF AERODYNAMIC
ADD-ON DEVICES ON AERODYNAMIC PERFORMANCE OF AN AUTOMOBILE: A
NUMERICAL STUDY. Journal of Automotive Engineering, 25, p.101.
Khokhar, A.A.S. and Shirolkar, S.S., 2015. Design and Analysis of Undertray Diffuser for a
Formula Style Racecar. International Journal of Research in Engineering and
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Leyva, J., 2014. Spartan racing revs up for SR-6 unveiling.
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UNDER TRAY DIFFUSER OF A FSAE RACE CAR
Trzesniowski, M., 2017. Verbrennungsmotoren Combustion Engines. In Antrieb (pp. 1-168).
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