A small research carried out as a part of one of my MSc modules, focused on analysing the impact of these "polemic" devices over the aerodynamic performance of the rear wing and general stability of a F1 racing car.

1. CFD study of Formula 1 Shark fins: Effect on the aerodynamic
performance and yaw stability
ABSTRACT
This year, Formula 1 has brought back to life an
aerodynamic device which disappeared a couple of
years ago: The shark fin over the engine cover. It is clear
that this element has a big impact on the aesthetics of
the car. In this research, a CFD study of the effect of
different shark fins has been undertaken in order to
establish a quantitative analysis of the effects on car
stability and rear wing performance that the device
produces. A baseline Formula 1 car was designed and
imported to CFD software Star CCM+. Two different fins
were added to a baseline car without the element. All
three geometries were tested in three different positions
related to the air flow: 0º, 4º and 8º of yaw angle. Forces
and coefficients of the rear wing were extracted in order
to make a comparison of each car at a certain yaw
condition. Pressure distribution and shear stress on the
wing surfaces, as well as wake vorticity were analyzed
with the aim of build a clear picture of how the
introduction of shark fin devices impact on aerodynamic
performance at the rear end of the car. Lateral forces
and yaw moment coefficients generated by the shark fin
were extracted from the simulations and results of the
three cars were again compared at each yaw scenario.
Results shown a loss of downforce generated by the
rear wing on straight line performance when the element
is introduced. However, as yaw angle is increased,
losses are reduced and flow tends to be uniform towards
the rear end. Moreover, the stability is highly improved
as a consequence of shark fin introduction.
INTRODUCTION
A racing car changes continuously as it is moving along
the track. How would aerodynamics change around it?
Yawed flows tend to change the balance of the car and
can lead to a loss in lateral stability and poor handling.
Many researchers studied the performance changes
produced when the car is cornering. (Milliken, Dell'Amico
and Rice, 1976) carried out a steady-state analysis of
car lateral stability. Nevertheless, all of them focused
their work on passenger cars. (Howell, 2015) performed
a wing tunnel test in order to determine how drag
coefficient varies with changes in yaw. Other effects of
cornering, such as side forces, are taken into account by
Okada et al. (2016) to determine Drag variations using
CFD analysis. But cornering is not the only reason why
the stability of a racing car can be compromised.
(Theissen et al., 2011) pointed out that a deep
knowledge of car’s behaviour under crosswinds is
essential in order to evaluate car performance. (Broadley
and Garry, 2000) studied the instability derived from the
braking manoeuvre.
This year, Formula 1 cars have introduced a new
element close to the rear end, with the aim of improving
yaw stability: An aerodynamic element called “Shark fin”.
(Dahlberg, 1999) found that the front end of the car
experiences a higher lateral force than the rear one
under yawed flows. The main aim of this research is to
assess through CFD simulation the real effect over the
aerodynamic forces generated as a consequence of the
introduction of different shaped shark fins, as well as to
define the role that the device plays in the lateral stability
of the vehicle. The introduction of the shark fin should
improve significantly car stability under yaw conditions.
Will the “Shark fins” stay in formula 1 longer? With the
purpose of answer this question, this research was
undertaken.
CFD MODEL
GEOMETRY
A Formula 1 car body and wing were designed using
Solidworks according to the dimensions within the 2017
Formula 1 technical regulations. Two different shark fin
models were added to the baseline geometry for a total
of three cars to test (Figure 1).
Figure 1: No fin, Spine fin and Square fin geometries

2. CAD models were imported into Star CCM+. All the
geometries were combined into different groups
according to its relevance in the final results (e.g., Wing
was divided into upper and lower surfaces, whereas the
body of the car was one single part).
MESH VALUES
Since the geometry had to be tested in different
positions, surface wrapper technique was applied to the
model. Another chosen model was Trimmer. The
combination of both models was translated into a
reduction of computational time spent as expecting
regarding results obtained by Pachpund et al. (2012). In
terms of mesh size, three different volumes were added
to the main geometry with the aim of gently reduce mesh
size towards the rear end of the car. Wing and fin mesh
sizes were refined since they are goal parts of the
research. An example of the refined mesh can be seen
in figure 2. Moreover, a contact prevention set was
applied to wing planes, in order to avoid the gap to be
closed.
Figure 2: Example of mesh refined at rear wing
BOUNDARY AND PHYSICS CONDITIONS
Inlet boundary was given a velocity of 60m/s and outlet
was defined as a flow-split boundary type. The flow is
considered turbulent. The k-epsilon model was chosen
as a turbulence model for all simulations. (Shetty and
Patil, 2013) implemented this model in a CFD analysis of
the external aerodynamics of a car with positive results.
CONVERGENCE
Results had been considered as full converged when all
residuals were below 1E-03. Results converged after
4000 iterations.
RESULTS AND DISCUSSION
0º YAW CASE
Forces in the rear wing
Forces and force coefficients were extracted from the
simulation and can be found in Tables 1 and 2. Results
revealed downforce loss of 3.7% in the spine fin case,
and about 7.3% whit the use of the Square fin.
Furthermore, drag force slightly decreased in both
cases. Since downforce reduction is considerable,
analysis of the flow was undertaken in order to
understand the reason.
No fin Spine fin Square fin
Yaw CL CD CL CD CL CD
0º 4.610 0.509 4.441 0.471 4.297 0.472
4º 3.675 0.482 3.416 0.465 3.585 0.451
8º 2.736 0.522 2.673 0.482 3.040 0.458
Table 1: Rear wing force coefficients
No fin Spine fin Square fin
Yaw DF Drag DF Drag DF Drag
0º 1392.2 153.7 1340.7 169.7 1297.3 142.4
4º 1341.3 175.8 1246.4 169.7 1308.2 164.7
8º 1167.1 222.5 1140.2 205.5 1295.6 195.2
Table 2: Rear wing aerodynamic forces (Newtons)
Flow structure
With the aim of understand the phenomena of force
reduction, wake vorticity was measured close to the rear
wing. Results can be seen in Figure 3. No fin and Spine
fin cases presented similar results, though slightly higher
vorticity values can be noticed in the region below the
main plane. However, a weak but perceivable vortex
structure appeared in the center of the wing, above the
flap plane.

3. Figure 3: Vortex structures at the wake for 0º yaw case (No fin, Spine
fin, Square fin.)
Studying this vortex in depth was observed that is
generated in the square fin and continues towards the
rear wing. Vortex structure impacts against the main
plane, generating the previously mentioned downforce
and drag loss. Evolution of this vortex as it moves
through the wing can be seen in Figure 4.
Figure 4: Vortex evolution through wing main plane
Wing pressure distribution
Static pressure distribution along the wingspan was
extracted from a surrounding area of the leading edge of
the main plane (Figure 5) and the flap (Figure 6).
Pressure distributions are symmetric as expected. In the
main plane, no fin and Spine fin cases show similar
distributions except from the two light curves on the
upper surface in the Spine fin case. Vortices coming
from the fin diverge producing a decrease in pressure,
thus decreasing downforce. Nevertheless, those vortices
are weak.
Figure 5: Static pressure distribution on the main plane
The main difference appears in the Square fin case. The
vortex created mentioned in the previous sub-section hit
the main plane, reducing the pressure in the upper face

4. and increasing it in the lower face. Thus, being the
cause of the decrease in downforce found when shark
fins were introduced.
Figure 6: Static pressure distribution over the flap (0º yaw)
Pressure distribution in the flap showed the same
results. The fluctuant pressure that appeared on the
main plane tips became low pressure zones on the flap
as a consequence of vorticity. The inverted peak created
by the square fin vortex was also noticed in the upper
face of the Shark fin case.
4º YAW CASE
Forces in the rear wing
All results are shown in Tables 1 and 2. As a result of
the yawed flow, a diminution of 3.65% in downforce was
noticed with no shark fin in the car compared to the
straight line case. Drag force suffered an increase of
14.43%. The introduction of the spine fin did not reported
any benefit in terms of drag or downforce at a yaw angle
of 4 degrees, showing an important reduction in
downforce compared to the car with no fin incorporated
drag forces are similar. As expected, the “Square fin” did
not show a massive difference over both previous
scenarios. However, a lower value of the drag force
allows the wing to be more efficient.
Flow structure
Vorticity in the wake (Figure 7) revealed some of the
reasons governing the wing performance. Windward
vortices were found to be weaker and leeward ones
stronger in all three cases as expected. The structure
generated by introducing the spine fin is indicative of the
downforce loss in the wing, since vortices are weaker.
Introducing the squared fin, vortices tend to be similar to
those found in absence of fin and a rise in the central
vortex generated by the fin was noted.
Figure 7: Wake vorticity for No fin, Spine fin and Square fin.
Since this last vortex seemed to be stronger that in the
0º of yaw case, vorticity in the trailing edge location of
the shark fin was measured in order to find out its effects
over the rear wing. Results in figure 8 show that the
structure moved upwards before hitting the rear wing,
and as a consequence of that downforce will be higher.

5. Figure 8: Square fin tip vortex
Wing pressure distribution
The vortex produced by the squared fin has migrated
upwards and the inverted peak of the lower main plane
surface disappeared. However, small effects of this
vortex can still be perceived in the upper surface, with a
small pressure decrease towards the center of the wing.
Hence, downforce loss between no fin and square fin
cases is less. The spine fin case showed a decreased
pressure gradient close to the right end plate. That
agrees with the weak vortex structured depicted in the
previous section, being the reason of performance loss
in this case. Peak pressure gradients were displaced
right as a consequence of the yawed flow. As expected,
the squared fin led the flow slightly straighter towards the
rear wing and therefore, the minimum value is closer to
the middle plane. In terms of the flap, the flow followed
the same pattern showing the decreased pressure
gradient in the right zone of the spine fin case. In the
windward side of the square fin case a bigger pressure
gradient was noticed, due to better flow alignment.
Figure 9: Pressure distributions in the rear wing at 4º of yaw
8 DEGREES OF YAW
Forces in the rear wing
As expected, the biggest difference was seen with a yaw
angle of 8 degrees. In the car with no fin the flow
detaches from the lower surface of the main plane,
causing a notable loss of downforce. Since the “Spine
fin” is not long enough to drive the flow straight towards
the rear wing, flow detachment was seen, although the
drag force is reduced in 7.6%. The “Square fin” had the
biggest impact over wing performance. A more
symmetric pressure distribution is translated into a less
flow detachment over the wing. Hence a substantial
increase in downforce and a slightly lower drag force
generated enhances the efficiency of the wing.
Flow structure
Windward tip vortices were stronger than the other 2
cases. At high yaw conditions, the fin aligns the flow with
the rear wing and generates more suction, enhancing
downforce.

6. Figure 10: Wake vorticity for No fin, Spine fin and Square fin at 8º yaw
In this case, wall shear stress (Figure 11) helped to
understand the effect of the fin. The flow in the lower
surface of the windward side detached and generated a
vortex close to the endplate. The effect disappeared with
the introduction of the spine fin and square fin increased
the stress on that zone, revealing that flow alignment is
better. Separation and downforce loss in the no fin case
was expected regarding the results obtained in (Gogel
and Sakurai, 2006).
Figure 11: Wall shear stress. Left to right: No fin, Spine fin and Square
fin
This separation and downforce loss in the no fin case
was expected regarding the results obtained in (
Wing pressure distribution
Figure 12 shows static pressure in the wing. In the main
plane a decrease in pressure in the square fin case was
perceived. That leads to an increment in rear downforce.
The minimum pressure peak was also displaced to the
center of the main plane, since flow hit the rear wing
straighter.
Figure 12: Wing pressure distribution at 8º yaw
In terms of the flap, the windward side showed higher
pressure in the no fin case as a consequence of the flow
separation produced. Improvements can be seen with
the introduction of the fins, being the square fin case the
most favorable.
EFFECT ON PERFORMANCE AND STABILITY
From a cornering point of view, the introduction of a
massive plate at the rear end of the car would surely
produce an important handling change. With the purpose
of measure the impact of the shark fin, yaw moment
coefficients were extracted from the model.

7. Figure 13: Yaw moment coefficient variation
Figure 13 displays the yaw moment coefficient for each
car at the different tested yaw angles. As can be
perceived straightforward, both square and spine fins
increase the yaw moment in the opposite direction of the
steering angle. However, curves corresponding to the no
fin and spine fin cases followed a similar tendency when
yaw angle becomes more extreme, whereas the shark
fin still increases until a value of -0.7076, which almost
doubles the value found in the no fin case.
Static pressure distribution over both sides of the shark
fin showed a notable differential pressure between left
and right surfaces producing a net side force. This lateral
force improves the stability of the car in potential
oversteering situations. Lateral forces generated also
allow the car to drive faster through corners. In addition
to these effects, downforce increase helps making the
car stable. (Howell and Le Good, 1999) stated the effect
of lift in yaw stability.
CONCLUSION
A CFD analysis of how the introduction of shark fins
affects the performance and stability of a F1 car has
been carried out. In terms of performance, downforce
loss is experienced in straight line with the presence of
the square shark fin. The longer the element, the greater
the decrease in downforce experienced. However, the
curve of performance loss is less pronounced when yaw
angle is increased. Regarding stability, results confirm
that for big side areas in the rear, stability is largely
improved. The square fin improves stability in cornering
and crosswind conditions. Results show that the benefits
obtained in yawed conditions using the square fin are
larger than the loss of wing performance experienced in
straight line. It is also clear as well that the spine fin does
not report the benefits of the square fin at yaw, stating
that intermediate solutions are not convenient.
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